The Science of Everything Podcast - Episode 151: Diet and Nutrition

Episode Date: February 1, 2025

An introduction to human nutrition, in which we discuss the nutritional importance and role of carbohydrates, fats, proteins, vitamins, and minerals, before considering the effects of malnutrition, how it is measured, and its prevalence around the world. We conclude with an analysis of basal metabolic rate, reviewing evidence concerning its variability across persons and factors that affect it. Recommended pre-listening is Episode 18: Biochemistry Basics If you enjoyed the podcast please consider supporting the show by making a PayPal donation or becoming a Patreon supporter. https://www.patreon.com/jamesfodor https://www.paypal.me/ScienceofEverything

you're listening to The Science of Everything podcast, episode 151, diet and nutrition. I'm your host, James Fodor. Today we're going to be doing the first in what hopefully will become a series of episodes focusing on diet and nutrition. So this is going to be largely an introductory episode. We're going to talk about the major human nutrients, so the macronutrients, carbohydrates, fats, amino acids, and then micronutrients, vitamins, minerals, and other things like fiber. I'm then going to talk about different types of malnutrition, so when nutrition is not adequate in various ways. So particularly talking about undernutrition and overnutrition as to different forms of sort of nutrition going wrong. We'll talk a bit about obesity and causes of vitamin deficiencies and so forth. And then we'll conclude today's episode by talking about basal metabolic rate, which affects how rapidly our bodies burn calories, which is obviously a very important.

component of, in fact, one of the major components of determining the balance between weight gain and weight loss. And so this will be useful background for a future episode where I talk about the science between comparative diets. Recommended pre-listing for this episode is episode 18, biochemistry basics that will provide you with some background relevant to some of the organic chemistry and biochemistry that I discussed, particularly with respect to the macronutrients. So without further ado, let's get started and start by talking about what is a nutrient. So nutrition obviously is the science of nutrients and how they're eaten and absorbed and used by the body. This raises a question of what exactly is a nutrient. So there are a number of

general definitions that you see which define a nutrient as sort of anything that's required by the body to grow and to carry out its functions and so forth. This seems a little bit general to me because definitions like that would encompass things like oxygen, for example, or a sufficient ambient temperature. But really, when we're talking about nutrients, we're talking about chemicals that the body needs to digest in order to function properly. So basically, a nutrient is something that you eat that your body can digest in some way that helps it to perform its functions, its metabolic functions and to sustain life and so forth. So that's are what is meant by a nutrient. And nutrients can be classified into two broad categories,

macronutrients and micronutrients. The difference between them is effectively the amounts that we need of them in our diet. So macronutrients are required in fairly large quantities, like many grams every day, and they provide the critical structural material like amino acids, lipids, and also energy that are required to build the key components of our cell membranes and the proteins and the enzymes and everything else that sort of keeps our body working. So macronutrients are the key building blocks and sources of energy for ourselves and for our body as a whole. By contrast, micronutrients are required in much smaller quantities, so usually milligrams or

even micrograms. And they do not form the key structures or provide the energy requirements that we need. Instead, they usually serve more niche requirements. So micronutrients are mostly vital. vitamins and minerals, and we'll talk about the difference between those in a moment. In addition, there's also fiber, which I'm not entirely sure where it fits, to be honest, because fiber is a bit unique in that it's not digested or at least not digested directly, so I'd put that in a bit of a separate category.

Again, we'll talk more about that in a moment. So what we're going to do now is go through the major classes of first macronutrients and then micronutrients, plus fiber at the end, and talk about what makes them chemically distinct, why they're important. and which aspects of or which components of these nutrients are particularly essential for the diet. And I'll also talk about some of the consequences of deficiencies of these different types of nutrients. Bear in mind that I won't be able to cover everything, particularly all of the vitamins and all of the vitamins and minerals, because there are quite a large number of them, and I won't have time to cover all the deficiencies and so forth. So I'll just touch on some of the major ones.

So carbohydrates are the first macronutrient that we're going to discuss. for many people, they form the majority of the diet in terms of caloric intake. Carbohydrates are compounds that are made up of different types of sugar molecules linked together. So by sugar molecule, we mean like a monosaccharide. And the general formula for such molecules is essentially carbons linked up with water. But what that means is that it's just carbon in a certain ratio with water. That's what defines a carbohydrate. Kind of makes sense, right in the name carbohydrate. A single unit of a sugar molecule is called a monosaccharide. There are different types of monosaccharides. Often they form ring structures, like cyclical ring

structures with five or six carbon units in them. That's quite common, although there's other forms as well. The simplest and most common, well-known monosaccharide, is glucose. Another commonly encountered monosaccharide is fructose. These monosaccharides, the main ones found of the diet, are all fairly similar, but there are slight chemical differences between them. Monosaccharides can be connected together, joined together, to form larger units. When you join two monosaccharides together, you form a disaccharide. An example of disaccharide is sucrose. You can also form larger carbohydrate molecules by combining more than two monosaccharides together. If you combine three to five-ish monosaccharides together, that results in a molecule called an oligosaccharide. And if you combine many,

many more dozens or even hundreds of monosaccharides, you form what's called a polysaccharide. Examples of these are starch, glycogen, and cellulose, which we'll talk about in a moment. So what differentiates is essentially subtle structural differences in terms of where the hydroxyl groups and other side chains are placed and the arrangement of the carbon atoms in the ring and so forth. And also then how many of these monosaccharides are. are linked up together and the precise arrangement between them. All of them are made up of the same key elements. It's just carbon and hydrogen and oxygen,

but the precise arrangement and length of the chain and structure of the chain is what differentiates them. Now, carbohydrates make up the large part of staple foods like rice, noodles, bread, and other grain-based products. Interestingly, however, carbohydrates themselves are not an essential nutrient. So that means that there are no carbohydrates that a human requires, in order to have a balanced diet. That being said, if you don't consume any carbohydrates,

first of all, it's often difficult to maintain your caloric requirements without consuming any carbohydrates. Of course, you can do that, but you have to be quite a lot of fat and protein. The other thing is that a diet that's insufficient in carbohydrates will lead to a state of ketosis, which has some undesirable side effects and can be dangerous. I'm going to discuss that in more detail later when we do comparative diets, and they talk about low-carb diets, particularly the ketogenic diet.

So carbohydrates are not, strictly speaking, an essential nutrient, but there are consequences if you don't have enough carbohydrates in the diet. That being said, it's quite uncommon for people to not have enough carbohydrates in the diet unless they're just not getting enough calories to begin with. In fact, often the issue is people, at least in modern Western context, consuming too many carbohydrates, which essentially just leads to excess caloric intake. But for now, let's continue to talk about the structural and functional differences between different types of carbohydrates in their nutritional aspects.

In food science and sort of often informally, the term carbohydrate often is used to describe a food that is particularly rich in complex carbohydrates. So like cereals, bread, pasta, and things like that. People often talk about those as carbohydrates or just carbs, which is a bit misleading because carbohydrate is really the key macronutrient that makes up the foods or that's contained in the food. It's not the food itself, but often there's a slippage in that usage. There's also a distinction between simple carbohydrates and complex. complex carbohydrates. So complex carbohydrates are basically foods that contain large quantities of oligosaccharides, or particularly polysaccharides. So these are sort of starchy foods or foods that have a lot of cellulose in them, so like foods derived from plants, especially whole grain foods. So those are complex carbohydrates,

so-called because the molecules are much more complex, right? They're much longer and more intricately branched and so forth. Whereas simple carbohydrates are mostly monosaccharides, maybe dis-saccharides, like glucose is the sort of simplest carbohydrate. Now, I've talked about some of the different types of carbohydrates classified based on their lengths, monosaccharide, disaccharide, oligocirates, and polysaccharides. I want to talk a little bit more about polysaccharides in particular because there's a vast array of these, and they're particularly important, and I think a little bit of understanding about their chemical differences

can help to pass some of the material that we'll be talking about later on and that you may be here in the discourse. So let's talk about starch to start out with. So starch is a polysaccharide that consists of, numerous glucose units joined together by a type of bond called a glycocytic bond. Starch is used by most green plants for energy storage, and therefore it's found in large quantities in staples like wheat, potatoes, corn, rice, cassava, and so forth. Pure starch is white tasteless and odorless powder, which is insoluble in water,

or at least in cold water. And there's two different types of molecules that comprise starch. So starch itself is not a single molecule, there's sort of two different, different molecules that make it up. There's a molecule called amylose and a more highly branched molecule called amylo pectin. So the amylose is sort of has a almost like a DNA helix structure, though, it's a single helix, whereas as I said, the amelopectin is much more branched and kind of complex. They're both made out of single glucose units, but they differ in terms of their overall structure and how those glucose units sit in relation to each other. Now, some types of starch can be digested by humans, but there are certain types of starch called resistant starch, which are those that

escape digestion from the small intestine. Resistant starch is one type of molecule that constitutes fiber because it's not digested. Now, starch is the polysaccharide that plants use, or most plants use, to store energy in their cells. Glycogen, you may be familiar with, I've talked about it before, is a similar molecule which is used by animals to store energy. it's a more highly branched version of amylopectin. So amylopectin is the branched version, well, glycogen is even more branched than that, but otherwise it's similar sorts of thing.

And humans, of course, can metabolize glycogen. I mention it here because it's important to keep in mind how these different molecules are related to each other. So we've got starch, which is plant energy storage, glycogen, animal energy storage. Glycogen can be metabolized. Starch sometimes, yes, sometimes no. Resistant starch is the one that can't be, and will pass into the large intestine. Now in addition to starch, there are a number of other types of polysaccharides that are consumed, particularly in plant matter, which humans can't digest or mostly can't digest. So examples include lignin and pectin. These are types of polymers that are typically found

in the support tissues and cells, cell walls of plants, and humans cannot digest these. Perhaps the most well-known example of a polysaccharide that humans cannot digest is cellulose, which again is a molecule that makes up the parts of the cell walls, of plants and humans also can't digest this. The reason we can't digest these types of polysaccharides is because we lack the enzymes required to break down the particular chemical bonds that join the monosaccharides together. So these types of polysaccharides that we can't digest or can't always digest constitute fiber because they are, they pass through the small intestine, mostly or

entirely undigested and then move into the large intestine. We'll talk more about what happens to them there a little bit later. Just what I wanted to emphasize at the moment is that they're quite a range of these different complex carbohydrates. Some of them can be digested, like obviously glycogen, because animals use that, also starch, some types of starch can be digested, whereas others like lignin, pectin, and cellulose cannot be digested. Now, another thing that I wanted to mention that's relevant to carbohydrates is this concept of the glycemic index. Glycemic index is a number from 0 to 100, which is assigned to a food, with pure glucose given the value of 100,

so that's why it's an index, because it's all relative to pure glucose. And the number represents how rapidly the blood glucose level rises two hours after consuming that food. So a food is considered to have a low GI if it's below 55, high GI if it's above 70, and then mid is sort of in between. Now the relevance here is that complex carbohydrates,

you know, those big chained or helical molecule, and so forth that require a lot of time to break down, those take longer to be digested and therefore tend to have lower GI values. That is, they have lower glycemic index values representing the fact that they take longer to digest and longer to release glucose into the bloodstream. They're all made up out of glucose, like all carbohydrates are made up out of glucose or can be converted into glucose, but they take different amounts of time to do so, depending on how complex the structure is essentially. I mean, there's other factors too, but that's a major component. So complex carbohydrates generally have low glycemic indexes, whereas simple carbohydrates,

ultimate simple one being glucose in this case, which has the highest value of 100, they have high glycemic indexes. So that's what glycemic index is. Now, what is the significance of this, other than it just sort of reflects the structure of the carbohydrate. So choosing low glycemic index foods can be useful for managing blood glucose levels in those with diabetes or pre-diabetes. So that can be a tool that diabetics or people at risk of diabetes can use. Though it's not a very precise measure because the rate at which blood glucose levels change is quite variable for each person. And so you really need to measure glucose levels, blood glucose levels more directly. But you can use the glycemic index as a food as a kind of a guide or as a way to help with managing those

sorts of conditions, you know, in consultation with your physician. Now, there is a separate argument to that, like separate from the issue of managing diabetes, whereby some people argue that lower glycemic index foods are better for weight control. And that is an issue that we'll talk about in the future episode where I talk about comparative diets. But again, I'm just sort of presenting it as background information here without discussing exactly the issue of its importance for diet, but it's important to understand at least what it is, sort of chemically. All right, so we've talked about carbohydrates, difference between simple and complex, and the fact that there are no essential carbohydrates, although if you don't have any carbohydrates

or very low, you will enter a state of ketosis, which can be problematic, but we'll talk about in a future episode. We're now going to move on to the second macronutrient, which are fats. Now, fats kind of have a bad rap because of their name, you know, fat is a negative word, but fats are an important macronutrient, and as we'll see, some fats are actually essential to the diet. So a fat is an ester of fatty acids, or a mixture of those compounds. So a single molecule of dietary fat contains multiple fatty acids. So you may recall from biochemistry basics or a previous episode, there's a sugar molecule called glycerol,

which kind of connects usually three fatty acids chains together to form the fat molecule. These are called triglycerides, because there's a glycerol and then three fatty acids connected to it, like a kind of a triple tail. And each of these fatty acid chains consists of a long, well, chain, of carbon atoms connected to each other. You may be familiar with the distinction between saturated and unsaturated fatty acids. This reflects whether or not all of the carbons that are bonded in a long chain are saturated with hydrogens or not.

And so by saturated, we just mean that the maximum number of hydrogens is a present bonded to all of the carbons. The alternative is to have fewer than the maximum number of hydrogens bonded to those carbons in the chain. And that's possible if you have one or more double bonds between carbon atoms. So the carbon atoms can form a single bond and then have two hydrogens each. Or they can form a double bond, like a given pair of carbon atoms can form a double bond, and then only have one additional hydrogen each, because they've used one of the four valence positions to do a double bond. A saturated fanny acid is one in which all three of the fanny acid chains of your triglycerol

have the maximum number of possible hydrogens. I should say that the same thing, the the fatty acid chains can vary dramatically in length. So many different types of fatty acids, depending on the length of the chains. An unsaturated fatty acid is one in which at least one double bond exists between the carbon atoms. So there's a less than maximal number of hydrogen atoms in the fatty acid chains. It only has to have one in the whole molecule to account as unsaturated fat, although you can have more than one. And that's called polyunsaturated fat. as distinct from mono-unsaturated fat, which just means a single double bond in that one molecule. In addition to this, there are two different subtypes of unsaturated fatty acids.

Siss-uns-unsaturated fats and trans-unsaturated fats. These are sometimes also called trans fats. You may have heard of these because there's been an increased awareness and interest of these in the last few decades, and it's become fairly widely recognized that trans fats are quite unhealthy, that they're not required nutritionally, but they can lead to increased risks of heart disease and diabetes and other health conditions. The important thing to understand is that the difference between trans and cis fats is how the double bond is formed or the structure of the double bond, because both of them are unsaturated, so that means they have at least one double bond. But the difference is essentially the chemical geometry of that double bond. So if you think about a double bond, right, between carbon atoms, each of those carbons involved in the double bond has sort of half of the tail on either side of there, right?

If you think about there's a left-hand carbon atom and a right-hand carbon atom, the rest of the fatty acid chain will go off to the left and to the right. So each of those carbon atoms that constitute the bond have half of the fatty-acet chain going off from each of them. Now, the issue is what direction, what relative direction do the fatty acid chain is going? A cis-unsaturated fatty acid chain has a kind of a kink in it, which means that the molecule has a kind of a bend in the middle of it, and that's because of the relative geometry of the two sides of the fatty acid chain. So basically, the fatty acid chain on the left goes kind of a bit down, and then the bit on the right goes, the one on the right goes a bit up, if you want to think about that way.

so it introduces a kink in the molecule. Whereas a trans-uns-uns-unsaturated fatty acid, the molecule is the fatty acid chain is mostly linear. So the arrangement of the two halves of the molecule with respect to the double bond is such that it's essentially a straight line, or very close to a straight line. So to put it simply, a cis-unsaturated fatty acid has a kink in it, whereas a trans-uns-unsaturated fatty acid does not.

And in that sense, a trans-unsaturated fatty acid is more similar, to a saturated fatty acid chain, which also is quite straight. So think of that like as a, as kind of rigid and straight, and they pack together tightly, whereas unsaturated fanny acid chains have kinks in them, and so they tend to be, they tend not to pack together as tightly. That's one of the reasons why unsaturated fatty acids tend to be liquids at room temperature, whereas saturated fatty acids tend to be solids, because the intermolecular forces have different strengths. Transfani acids do occur naturally, so there's small quantities of transphanic acids in and dairy, but they're most common in highly processed foods, like margarine, cakes, cookies,

and shorteninges. They result from the unintentional byproduct of artificial hydrogenation of plant unsaturated fats. So hydrogenation refers to the process of adding hydrogens to an unsaturated fatty acid to make it a saturated fatty acid. Hopefully the name makes sense, right? Because if you have an unsaturated fatty acid, that means that it has some double bonds in it, if you add hydrogens to that to insert across the double bond, that means it goes from having not the maximum number of hydrogens to now being saturated with hydrogens. And the double bond goes away, and you now have a saturated fatty acid. So hydrogenating and unsaturated fatty acid is what you do to make it a saturated fatty acid.

This is a process that is used to produce certain types of foods, like margarine, for example, which is made by hydrogenating, unsaturated fatty acids taken. from plants to make them saturated fatty acids, which are then closer to a solid and room temperature and have the consistency of margarine. And so it was found only a few decades ago that this process of artificial hydrogenation produced some percentage of byproducts, of unintentional byproducts of these trans unsaturated fatty acids. Because remember, the goal of hydrogenation is usually to produce a saturated fatty acid, so the trans unsaturated fatty acids was not intended. But once this was discovered and their negative health effects were also determined. Then, at least in most

Western countries, I'm not sure if this is true everywhere, but at least in the European Union, Canada, US, Australia, New Zealand, new regulations were introduced to eliminate, to change the manufacturing processes that are used for hydrogenation to thereby eliminate or almost entirely eliminate trans fats from these sorts of products. The World Health Organization has set a goal to completely eliminate industrially produced trans fats by the end of 20 of 25, though I don't know if that will happen. Trans fats should not be a significant issue for most people living in developed countries these days. You will still see small amounts listed on like nutritional labels because there are small amounts of naturally occurring

quantities and meat and dairy, but mostly the artificially produced version being eliminated by changes in industrial practices. But it's still important to understand what these are and how they relate to the cis-unsaturated fatty acids, which are, which are more common. in humans fats are used both as a store of energy as well as a structural element to form important components of the cell membrane in their storage role fats are very energy efficient so one gram of fat contains about nine kilocalories whereas one gram of carbohydrates and one gram of protein both only contain about four killer calories. So in other words, fats are more than twice as energy dense as carbohydrates and protein. And that's one of the reasons people think of them as kind of fattening, right? Because for a

given mass of fat, then the body does extract a little more energy from it. Of course, there's more to it than that, but they are a very energy dense food. However, unlike carbohydrates, there are some essential fatty acids. So you may have heard this phrase, essential fatty acid. So what that refers to is certain fatty acids. So remember the fatty acid are the chains that are connected together by the glycerol molecule. There are many different types of them, depending on how many unsaturated bonds they have, and the length of them, and sometimes some other differences as well. Some of these fatty acid chains cannot be synthesized by humans, but are required in the diet. And so these are called essential fatty acids. In particular, mammals lack the ability

to add double bonds to fatty acids beyond carbon's nine. and 10. So certain types of longer fatty acid chains, in particular, omega-6 linoic acid and omega-3 alpha-linoic acid, are essential for humans in the diet. These two different essential fatty acids act as the starting point for the creation of other types of unsaturated fatty acids, which have even longer carbon chains. So there are other types of, many other types of fatty acid chains that humans can't synthesize de novo, like from scratch, but we can't synthesize. We can, them if we have these two essential ones as a starting point. These are often abbreviated as omega-6 and omega-3 essential fatty acids.

So these are the only fatty acids that are essential to the diet. We don't need very large quantities of these, but they are an essential nutrient because we can't synthesize them ourselves. All right, so that concludes the discussion of fats. Let's now move to the third and final category of macronutrients, which are proteins or amino acids. So proteins form the basis of the fats. form the basis of many structures in an animal body, muscles, skin, hair, and so forth.

And they also make up the enzymes that control chemical reactions throughout the body. Each protein molecule is composed of amino acids that form long chains. There's 20 different types of amino acids that are found in the human body. And so the precise order of these amino acids in these protein chains determine the structure and function of each of the proteins. We've talked about all this in previous episodes. So I'm not going to go into too much of the detail of that. Each protein molecule is comprised of these amino acids, and amino acids contain in addition to carbon, hydrogen and oxygen,

which are sort of the standard in all of the macronutrients. They are unique in also containing significant quantities of nitrogen and sometimes sulfur as well. So carbohydrates don't contain nitrogen or sulfur, and fatty acids as far as I know don't either, but amino acids do. So this inclusion of particularly nitrogen is one of the things that distinguishes amino acids from the other macronutrients. Now, in all animals, some amino acids are also. Some amino acids are essential. And again, an essential nutrient is one that cannot be synthesized or synthesized in sufficient quantities and therefore must be consumed in the diet. A non-essential amino acid is one that can be synthesized in the diet. So as we've discussed,

there are no essential carbohydrates and most fatty acids are not essential, but there are particularly two, the omega-6 and omega-3, which are essential for mammals. As for amino acids, there are nine of the 20 amino acids that are considered essential. that humans cannot synthesize. There are six other amino acids that are considered conditionally essential, which means that their synthesis can be limited under certain unusual conditions, like in premature inference, for example, or people suffering from certain types of diseases. But for most healthy individuals, they should be able to be synthesized. And then there are six amino acids that are considered non-essential, so that they can essentially always be synthesized in sufficient quantities,

assuming, of course, you have sufficient caloric intake, which is needed for synthesis of anything. So if we combine the conditionally non-essential and non-essential amino acids together, we have nine essential amino acids and 11 non-essential amino acids. So roughly half of the amino acids need to be eaten, and the other half don't. The recommended protein intake for a 70 kilogram person is only about 60 grams per day. So it's not a very large amount, and that's already quite a lot more than the total requirement for all of the essential and conditionally essential amino acids, which is only about 15 grams per day. So although about half of the amino acids are essential, we don't actually need to eat that much protein in order to consume enough of the essential amino acids. Obviously, it will be a bit different if you're doing bodybuilding or something like that. That's something we'll talk about in a future episode as well because there's a lot of misconceptions around there.

But for an average weight person, you only need about 15 grams in total of all of the essential and conditionally essential amino acids. The reason that essential amino acids, of course, are important is because we need all of the 20 amino acids. amino acids to make up the different proteins that are necessary for the body. And effectively, every protein is going to need at least some of each of the amino acids, at least for the longer proteins. And so there needs to be a sufficient pool, a reservoir, available of all the different types of amino acids. Otherwise, the body just won't be able to synthesize sufficient proteins. So that's why you need to have enough of them.

Amino acids are recycled. So that's one of the reasons why we don't need a very large amount each day, but we do need a sufficient quantity of the essential amino acids. All right, so that concludes discussion of the macronutrients. So we've talked about carbohydrates, fats, and amino acids, proteins. And what we found out is that the only essential nutrients, really, in these groups, are the essential fatty acids, so the omega-3 and the omega-6, and then the nine essential amino acids. Though we don't need very large quantities of those. We do need to consume them. Now, the next set of nutrients we're going to talk about are micronutrients. So these are nutrients that,

do not provide much of a caloric intake, and are only required in quite small quantities. Micronutrients are divided up into two main classes, vitamins and minerals. So let's start by talking about vitamins. Vitamins are organic molecules, which are essential to an organism in relatively small quantities. One thing that's important to realize is that most of the vitamins, or possibly all of them, are not a single molecule. So you may know many of the vitamins are given letter and number names, like vitamin A, vitamin C, vitamin D, and so forth. But most of these vitamins are not a single molecule that has a chemical formula. They're actually a closely related set of molecules called vitamins.

Vitamins cannot be synthesized in an organism, insufficient quantities for survival, and hence they must be obtained in the diet. So essentially by definition, all vitamins are essential nutrients. So let me just talk briefly about some of the major vitamins. Again, I won't go through all of them because it becomes just a bit of a, becomes too much of just reading through a list, but I'll mention a few of them. So vitamin A, many people know about this, it's very important for normal vision because it's used to synthesize beta carotin, which is a component in our rods and cones. But it has other uses as well.

So vitamin A deficiencies can lead to various types of blindness. There's thiamenzyman, which is a co-enzyme that's used in energy metabolism in the nervous system. A co-enzyme is basically a molecule that helps out another enzyme to perform a catalytic function. Deficiency of thiamine can lead to a condition called berry-berryberry, which is particularly known historically in sort of East and Southeast Asian countries because thiamine deficiency could result from eating a diet that's predominantly composed of white and rice. There are many different types of vitamin B vitamins. One particularly important one is vitamin B6, which is part of a co-enzyme used in amino acid metabolism. And deficiency in B6 can lead to anemia, nerve damage, seizures and quite a few other issues like that.

And so vitamin B12 is a co-enzyme that's used in DNA synthetalism. and deficiency of B12 can lead to anemia and numbness of the extremities and a variety of other conditions. Vitamin C is important for the immune system and for collagen that keeps the skin firm. Deficiency of that leads to scurvy, which I think many people have heard of. Vitamin D is important for absorption of calcium and maintaining phosphorus levels in the blood. Deficiency of vitamin D can lead to conditions. like osteoporosis and also rickets. Vitamin K is important for blood clotting

and deficiencies of that can lead to various clotting disorders. So that's an example to give you the sense of what vitamins are and what they do. So many of them act as coenzymes facilitating a particular enzymic reaction. So they don't actually perform the catalysis itself, but they assist the catalyst

in basically getting the molecules into the right relative deposition. Again, we've talked about that in previous episodes. We want to talk about protein, structure, and function, what a coenzyme is. So many of these vitamins are coenzymes that we cannot ourselves synthesize. Now, something you may remember about enzymic reactions is that an enzyme is not used up in a reaction, which means you don't need very large quantities of an enzyme in the body, typically, because you only need enough to catalyze enough of the reactions. You don't need it. It's not used as sort of fuel for the

reaction, so to speak. You don't use it up. A single catalyst can catalyze many, many reactions of the same type because it just keeps going on, right? It keeps doing its thing as long as until it's eventually broken down. So because many vitamins act as co-enzymes, that means that they're not used up in each reaction, and therefore we don't need very large quantities of them. This is one of the reasons why they are micronutrients, because we only need a fairly small quantities of them, but the flip sides of that is that they are extremely important because we need these chemical reactions to occur for normal metabolic function, and if we develop a deficiency of them, then there are going to be problems. So I think I talked about half a dozen or so. Different health organizations,

I think, lists slightly different numbers of vitamins. I'm not entirely sure why this is. I think that this may have to do with how exactly they're classified, but I think typical lists include 13 or 14 different vitamins. Another point of confusion that I should mention is that all vitamins are given a letter and or number designation, so vitamin A, C, D, and E and K. All of the other vitamins are given a B a B1, B2, B3, B3, B5, B6, B7, B9, and B12. In addition, vitamins also have a, like a chemical name. For example, vitamin B2 is the same thing as riboflavin. Vitamin B9 is the same as folic acid or folate.

So don't get confused. There are sort of different names to refer to the same thing, and usage is not 100% consistent about exactly how something is described. Also, if you're wondering about why the weird naming convention, I did read up a little bit on this. As far as I understand, vitamins were discovered in the early part of the 20th century, and initially there was a naming convention that assigned different letters to them, but over time, some vitamins were realized to be, oh, these is actually the same thing,

so we should use the same letter and not use two different letters for the same thing. Or some things that were thought to be vitamins, were later discovered not to be vitamins, and so the letter was abandoned. And so this is how we kind of ended up with the weird system we have, where it's like A through E and then all the way to K, and then there's a bunch of Bs that all have different numbers. So it's basically historical accident relating to how they were initially named and discovered and things like that. So as far as I know, there's no real deep meaning to the numbers and letters and things themselves.

All right. So that concludes our discussion of vitamins. Let's now move on and talk about the other type of micronutrient, which are minerals. Now, what differentiates a mineral from a vitamin is that minerals are inorganic. They consist of metallic elements, essentially, whereas a vitamin is an organic molecule that cannot be synthesized, usually relatively small organic molecules, not like huge macromolecules, but they can be, you know, moderately complex molecules, whereas a mineral is just a single element, but a metallic element. Minerals have a similar importance to vitamins, but whereas vitamins mainly serve as co-enzymes,

minerals mostly, not entirely, but minerals mostly are required as metal elements that form the catalytic core. of an enzyme. So it's not an enzyme by itself, but it's needed as part of an enzyme. Essentially the reason for this is because metals have a more complicated and intricate and variable valence orbital arrangement, which allows them to kind of bring together many different molecules or parts of a molecule in very specific arrangements. So if you're interested in this, I did do an episode talking about inorganic chemistry. That was episode 130, transition metal chemistry specifically not all metals are transition metal but at least it will discuss a number of the ideas there so part of what i discussed in that episode is why especially transition

metals are so useful as catalytic cores for many enzymes and so that essential chemistry is why we need most of these minerals in our diet is because we need them to serve as the catalytic core that brings together different components so that the enzyme can do its work and again this all also explains why we don't need very much of them because we don't, because an enzyme is not used up in a chemical reaction, so we don't need very large quantities of all of these minerals, just enough to constitute a sufficient amount of the enzyme to produce enough of the product. There are some exceptions to this. So calcium is actually has a much broader range of uses than just enzymatic. It also is an important signaling molecule, for example. Calcium is stored in pretty much all cells

and is an important secondary messenger, which I've talked about in episodes where we talk about cell signaling. And also, of course, calcium and phosphorus are both important components of bones, which form the actual structure of the bone. So other minerals that are not the transition metal elements include chloride. So chloride is an important electrolyte, helps maintain fluid balance, and also helps to maintain the electrical charge of cells. There's potassium, which also acts as an electrolyte and helps to maintain the electric charge of cells. And also sodium. Again, an electrolyte helps to maintain fluid and electrical balance. And sodium and potassium in particular are important for maintaining the electrochemical potential, which allows nerve cells

to send impulses and communicate. So that's important for our nervous system function. So not all minerals are involved in catalysis, but many of them are. So particularly copper, iodine, magnesium, magnesium, malibonium, selenium, zinc, and did I mention iron? I think I said that. They're all involved in catalysis in one form or another. And these are particularly required in the smallest quantities. We can loosely classify minerals in terms of the ones that are needed in somewhat larger quantities and the ones that are needed in even lower quantities. The ones that are needed in larger quantities are those that have non-catalytic uses. So I've already mentioned them, calcium, chlorine, phosphorus, potassium, and sodium. All of these serve as a structure, well,

calcium and phosphorus have structural roles like in the bones and teeth, and then calcium, chlorine, potassium and sodium all have important electrolytic functions, calcium also being an intracellular signaling molecule. Magnetium's kind of the old one out here because it's a transition metal element and it's also does serve catalytic functions. I'm not entirely sure why we require more of it than the others. It is required for processing ATP so that may be one of the reasons because that's obviously a very, very important reaction for producing energy. Now all of the other are required in much smaller quantity. So cobalt, copper, chromium, iodine, iron, magnesium, selenium, and zinc, all form a catalytic role in enzymes, and therefore we don't

really need very much of them at all. But still are an essential nutrient. So all of these minerals are essential nutrients. Obviously we can't synthesize them. There's no way to synthesize inorganic materials from organic base, and so they need to be consumed in the diet. One important factor about minerals, and this applies to vitamins as well, is that they can be present in the diet, but they will only be actually available for usage if they're absorbed appropriately, so if they're actually absorbed in mostly the small intestine. In order to be absorbed, minerals must be soluble and sufficiently readily extractable by the organism. So bioavailability is actually a very complex issue, and it's because it's affected by many different factors.

In particular, it's affected by the food that the mineral or vitamin is found in, including the fiber content of that food and other nutrients, other vitamins and minerals, the macronutrient balance and other things like that, that the mineral is found in. It's also affected by the health of the person, the physiological state, and so it can vary from one person to another. This is one of the reasons why just taking supplements of vitamins and minerals is not considered as good as consuming them as part of a healthy balanced diet because the bioavailability is not necessarily as good in an isolated form. But of course, there's many contextual details there. And that's something I'd like to discuss in more detail in a future episode. But I think it's just something

that's important to recognize that it's not simply the amount of vitamins or minerals that exist in the diet. They also need to be sufficiently bioavailable for them to be absorbed appropriately. All right, so that concludes our discussion of the micronutrients. And now we'll just say a few words about fiber. So dietary fiber consists of plant components that are not digested by human digestive enzymes. So particularly it consists of polysaccharides from plants. Remember polysaccharides are the big long most complex forms of carbohydrates consisting of very long chains of the monosaccharides So it includes cellulose chitin resistant starch So starch is this plant storage molecule some types of it can be digested but some not so resistant starch is the

The type that can't be so that's fiber lichen Pectin beta glucans and most oligosaccharides So oligosaccharides are like the medium-length Saccharides between the Dysaccharides and the polysaccharides so there's a wide range of different types of carbohydrates that fall under this category of of being fiber, dietary fiber, because they can't be digested by our own enzymes. Now, it's a little bit complicated because some dietary fibers can be digested, but not by our own cells, but they are fermented by bacteria living in the large intestine. And this fermentation leads to production of gas, so that leads to flageolence,

and also various other types of nutrients, which then can, or at least some of them can be absorbed by the large intestine. So we actually get some nutrients out of the fiber, not directly, but indirectly through the, essentially the byproducts of the digestion of these materials by fermenting bacteria and the large intestine. I wasn't able to get any clear indication of what proportion of components of dietary fiber typically are fermented, or like how much of the caloric value of dietary fiber is realized through intestinal bacteria. But that's something that I would like to look into for a potentially future episode. Dietary fiber is not a nutrient in the sense that it's not absorbed by the body,

like all of the previous ones we've talked about, although, as we've said, some components of it can be absorbed indirectly after it's fermented by bacteria, but not all of it is. Some fibre is just passed out in the fecese as indigestible roughage, but fibre still is important because it serves a number of nutritive functions, and one appears to be improving the bioavailability of certain vitamins and minerals. It seems that there requires sufficient fiber in order to be absorbed appropriately, Another function of fibre is to serve as roughage for the food, so that helps with the digestive

process, helps avoid constipation. And there appear to be a wide range of other important functions of dietary fiber as well. Something, again, probably will discuss further in a future episode, but it's a complicated issue, exactly what the function of fiber is. It is clear that it's a very important part of a balanced diet, but exactly what its function is is less clear than the other nutrients we've discussed. By definition, fiber is only found in plant-based foods. So particularly legumes, whole grains and cereals, vegetables, fruits, and nuts contain large quantities of fiber. Typically, the more a carbohydrate is processed, the less fiber it will contain. And that sort of should make sense because fiber consists of complex carbohydrates.

If you process them, that almost inevitably means breaking them down into smaller components, which often tastes sweeter. So like sucrose, for example, with diaccharide or glucose fructose. So processing can make them taste nicer and be a bit easier to eat. So white bread is softer than brown bread. But the trade-off there is that they become more easily digestible, and so they cease to be starch because, sorry, they cease to be fiber, because now we can digest them as simpler carbohydrates. So that's why the best sources of fiber are relatively unprocessed, whole-grained foods.

All right, so that concludes the discussion of the different types of nutrients. So let's just revise again, what are the essential nutrients that humans require? Obviously, we require enough water. I haven't really talked about that in detail, but water is a nutrient as well. Again, probably save that for an episode where I talk about the urinary system, and we'll talk about water intake and things like that. But water is a nutrient. And we also need sufficient caloric intake. Beyond that, carbohydrates have no essential nutrients that we actually need.

Though, again, if you don't have enough, you can enter ketosis, which can be problematic. But there are no essential carbohydrates. In terms of fats, we have two types of essential fatty acids, so the omega-3 and the omega-6. We have nine essential amino acids, which need to be consumed to form all of the proteins in our body, but only in relatively modest quantities. We then have 13-ish vitamins, which are the small organic molecules that cannot be synthesized. Most of them act as co-enzymes to facilitate different metabolic chemical reactions. And then we have the minerals, 20 or so different inorganic metals, which either

function as electrolytes like sodium and potassium and so forth, or they serve a catalytic role. So they form the functional center of the catalytic site of a catalyst. And so that's enzymes like iron and chromium and so forth. In addition to all those, we have fiber, which is indigestible plant-based polysaccharide, which serves as important roughage and helps to improve the bioavailability of other nutrients and seems to support the functioning of the digestive system more broadly, the exact roles are still not fully understood. So those are all of the essential nutrients that humans need to survive.

I'm not going to talk about the exact numbers and things that people need of all these things here. You can look those up and different health bodies in different countries have slightly different requirements and it depends on things like your age and your sex and your height and weight as well. So you can look up that information for yourself. We're just talking more conceptually here. Now I'm going to talk about what happens when we don't or don't achieve these essential nutrient requirements. and that's malnutrition. One of the easiest ways of characterizing malnutrition,

not the most accurate, but one of the easiest, is something called the body mass index or BMI for short. This is something that you've almost certainly heard about. This is a metric that's used to describe a person's weight relative to their height. So it's measured as kilograms per meter squared, and so essentially what you do to calculate your BMI is you take your weight in kilograms divided by your height squared, measured in meters, and that's your BMI.

The typical classification is that the ideal or normal, maybe normal is not quite the right word, because actually in many countries, most people are not in the normal range, but maybe ideal is a better word. The ideal BMI range for best health outcomes is around 19 to 25. You'll see slight variation on that, but roughly that number. Anything under 19 is considered underweight, and anything over 25 is overweight. and anything over the 30 is considered to be very overweight for which the word obese is typically used

and there's actually multiple different classes of obesity. Now, there are many criticisms of the BMI metric. BMI does not differentiate different types of body mass. In particular, it doesn't differentiate between muscle or fat or differences in builds which differ between like ethnic groups or your genetics and things like that. However, it is useful in making gross comparisons between groups of people, between populations.

where often those things, individual differences kind of average out. There are differences in terms of populations, so Asian populations tend to have lower BMIs, whereas, say, Pacific Islander populations tend to have a higher BMIs, even adjusting for health and other things. But even so, it still has a use as a very simple to calculate and easy to measure metric. A more precise method to measure someone's nutritive status is the body fat percent. And this is just the percentage of someone's, a fat to someone's entire weight. And it's a more accurate measure of whether someone has,

effectively is getting too many or too few calories in their diet. Guidelines are about 32% body fat for women and about 25% for men are used as a cutoff for obesity. So you want to have significantly lower than that. And that being said, though, there is a fairly high correlation between body fat percentage and BMI. So one study in the US that I found computed a correlation of about 0.7 between BMI and body fat percentage. for men, and about 0.85 for women, so an even higher correlation for women. This is under the age of 65. The correlations are a bit lower for above the age of 65. So in the general population, someone's BMI tells you a fair bit about their health status, like on average, but it is an

imperfect measure. And so body fat percentages are a more precise measure. In addition, there are some very interesting studies which look at the relationship between body mass index and mortality. These mortality curves are the basis or from one of the basis of what normal or ideal weight is defined to be. The way this works is you measure the body mass of a whole bunch of different people in a population and then you follow that up over time and see what proportion of people at different BMI see how many of them die of different types of conditions. So this is the mortality rate over a period of time. often over many years. And one study that I looked at from the Lancet, which used the statistics for

several million people, I believe. And this study was conducted in the UK and followed people for multiple years. So this is one of the more comprehensive studies to look at the relationship between BMI and all-cause mortality. And the graph that they plot, so has a measure of mortality rates on the vertical axis, so how many people die of a particular condition, or of all conditions. And then on the horizontal axis, they have BMI. So if there was no relationship between BMI and mortality, you would have a flat line, which would just mean that your mortality rates are independent of BMI. It's unaffected by body mass index. Now, what you tend to find for almost all conditions, not quite every condition, but the vast majority of conditions, and for all-cause mortality as well,

is what's sometimes called a J-shaped curve. It's a J-on-at-side, right? So it's a little bit of a a misnomer. Think of a V is a little bit easier, but it's like an asymmetric V. So what this means is that for people who are underweight, mortality is high, and then it goes down and reaches a minimum around 20 to 25, 19 to 25-19-to-25-ish, and then it starts going up again with higher BMIs. And once you start to get to really high BMI's, like 40, 50, mortality becomes very high. This has been found in a wide range of populations across the world. The study that I'm talking about from the Lancet, it was just a more recent, very well-controlled, very large one in the UK, and it's found across a wide range of conditions as well. Communicable diseases, non-communicable diseases, injuries,

cardiovascular disease, all sorts. The exact shape differs between the types of conditions, so unsurprisingly, conditions more centrally related to obesity, like cardiovascular health, for example, have a more pronounced shape, whereas for accidents, it's less pronounced. But for almost every type of condition, very underweight people or very overweight people have much higher mortality rates. So this is the basis, or one of the main basis, for why that sort of 19 to 25-ish is considered to be ideal weight, because this is where your mortality rate is lowest. Now, it is important to emphasize that these studies are observational. They're not experimental studies. You can't really assign people to different BMI's and then see what happens to them

over many years. That doesn't really work ethically or practically. However, the Observational studies have now become very large, like covering millions of people, and the one that I'm looking at from the Lancet has a number of very, I think, very well-implemented controls. So they look at smokers and non-smokers separately, for example, and they find very similar patterns. And they have additional controls for things like age and income and other factors as well, which allow them to sort of statistically adjust for these, which you can do fairly well over very large populations. Of course, as we've discussed, BMI is not a perfect measure of nutritional status. And so if we actually measured body fat percentage, which would probably be a better measure,

then the relationships would probably be even more sort of precise and sort of relevant. But that's, you know, body fat percentage is expensive to measure. You can't do that with millions of people, so BMI is used instead. But even so, even with this imperfect measure, we still see very reliable and robust associations between mortality and BMI. So this is something that's important to bear in mind. So again, these observational studies don't directly prove that BMI causes mortality, but in combination with very many other factors, it seems that there's very strong evidence that

being overweight increases your risk of many forms of disease and being obese, increases your risk of disease even further and so forth as you increase your BMI. Now, the heightened mortality rates for underweight persons are interesting, because in those cases, it's less clear that the mortality is due to being underweight versus the underweight, the underweightness being due to some other condition. So being sick, for example. An example would be people who have cancer very often lose a lot of weight. And so in that case, what's causing the weight loss is the cancer, not the other way around, right? But, so it depends on the condition. It does seem that being very underweight weakens your immune system. It means you don't have the

reserves necessary to get through physiologically difficult circumstances, and it means that you don't have all of your metabolic processes working at peak efficiency. So being underweight, and being overweight both bad for health in the long run is essentially the takeaway from these sorts of studies. So that's why these sort of j-shaped curves that show both being too fat and too thin, to put it crudely, are both bad for health, gives rise to this idea that malnutrition consists of two different extremes, essentially, undernutrition, which refers essentially to having insufficient nutrients, particularly insufficient caloric intake, or the flip side is overnutrition,

having too much choloric intake or too many nutrients overall. So this is a very complex issue, and I'm only going to give a brief introduction to some key terminology and some key facts here. Hopefully we'll be able to discuss some of the issues with particular types of deficiencies and particular conditions in future episodes. But for now, let's just introduce the notion of undernutrition.

And in particular, I want to explain protein energy undernutrition. So this is a form of malnutrition which results from lack of dietary protein and or calories, but in different proportions. So there's actually two different conditions. And you can have both or you can have both of them or you can have one or the other. So there's a condition called Marasmus, I hope I'm pronouncing that correct, which is a severe form of malnutrition characterized by energy deficiency. So the classic form of marismus is just that you have insufficient calories, but with sufficient or close to sufficient amino acid intake. And so this is, I think,

the most classic form of people might colloquially describe as starvation. You just don't have enough calories. Your other essential nutrients might be more or less met, but you're not getting enough caloric intake. And this mostly occurs in children because they're growing and so they particularly need more calories, you know, relative to their size than adults do. And they're particularly vulnerable in cases of shocks or famine and disasters and so forth. Now there is another condition called Koshior core, tricky word, which is a type of malnutrition caused by severe protein deprivation. so insufficient essential amino acids. In its pure form, the person is actually getting sufficient caloric intake,

but just insufficient essential amino acids across the board. Although you can have both, right? So in many cases, there's insufficient caloric intake, but particularly insufficient protein intake. One of the manifestations of this condition is an enlarged liver, which is a response to the insufficient protein intake. And so particularly children with this condition have the appearance of having enlarged bellies. So this is mostly found in sub-Saharan Africa, and so you've probably seen images of children with this condition, of being very skinny bit with enlarged bellies. That's because of the enlarged liver. And that particular condition, as I said, as a result, Koshiorkor is a result of insufficient protein intake, specifically. Worldwide, every year, there are about 200,000 deaths due to protein energy malnutrition. So this is sort of classical lack of protein intake and or lack of nutrient intake. Now this is down from about

600,000 in 1980. So we're going in the right direction, but still a shockingly large number, and most of these are in sub-Saharan Africa. However, this form of protein energy malnutrition, which people might think of the sort of starvation, you know, starving children in Africa, this accounts for only a minority of deaths due to malnutrition. Every year there are about one and a half million child deaths due to low birth weight and about another million deaths from conditions exacerbated by wasting, which means low weight for your height, or stunting, being too short for your age, or both, which is just called underweight. These conditions mostly affect children, and generally don't kill directly.

So, typically don't die directly from being underweight, or like wasting or stunting. Rather, what tends to happen is it weakens the immune system and leads to various other conditions, which it then serves to exacerbate or make your body weaker so that it can't handle infections or other conditions. And so this 1.5 million from low birth weight plus another million from wasting and stunting is an estimate based on how many deaths that are directly caused by something else are attributable to malnutrition. And globally in 2022, about 150 million children under the age of five are estimated to be stunted. Again, that's too short for your age. And another 50-ish million were estimated to be wasted, which is too thin for your height.

So about 200 million in total. The number of people dying every year of sort of straight up lack of caloric intake is relatively small compared to the number who are dying from conditions exacerbated by malnutrition. And many of these are not necessarily lack of calories, but can be lack of other essential nutrients as well. So we talked about quosci core, which is due to a lack of essential amino acid intake. but there can also be conditions that arise from lack of essential fatty acids, lack of vitamins, lack of minerals. Vitamin deficiency in particular is common in many parts of the developing world, especially sub-Saharan Africa and the Indian subcontinent. Deficiency of any particular vitamin usually results in a characteristic condition, so I discussed some of those before. I'm not going to go through them again. I will mention one though vitamin A deficiency because it's so important.

Vitamin A deficiency affects about one-third of children under the age of five worldwide. and every year it leads to hundreds of thousands of deaths and a similarly large number of cases of blindness, which is particularly tragic because vitamin A deficiency like most vitamin and mineral deficiencies is extremely easy to prevent. These can be prevented by supplementation, which is extremely cheap. Another method that's been adopted by many countries around the world is food fortification. So fortification is the process of adding micronutrients, particularly vitamins and minerals, to foods as a way to increase the intake and reduce dietary deficiencies. So food fortification has been an extremely successful method for reducing, not eliminating,

but reducing micronutrient deficiencies in many parts of the developing world. Food fortification occurs in developed countries as well, but it's occurred for longer and is less necessary because of greater access to food. Many types of foods are fortified. It's particularly common to fortify staple foods to include particularly, particular nutrients that are due to the soil or climate of the region inherently less likely to be consumed in a normal diet. So one well-known example is the fortification of salt with iodine. So this is called iodine salt. That's been used in the US since World War II as a way to prevent goiters,

which arises from a lack of iodine. But many other types of vitamins and minerals have been fortified in foods in different countries. So many programs that are used to donate staple crops to developing world countries, these grains are fortified with micronutrients like vitamin A, iodine, or folic acid as a way to improve their micronutrient quantities. Wheat flour in the UK has to be fortified with iron, vitamin B1 and vitamin B3. So the exact micronutrients that are fortified in which foods they're included in vary by country. Most countries around the world, if not all countries, practice food fortification to some degree. And it's a very, very effective public health strategy. Okay, so let's just conclude this section by talking briefly about overnutrition.

This is a subject that will require an entire episode to itself, possibly multiple episodes, so I'm just going to give it the barest introduction here. By overnutrition, essentially what we mean is excessive intake of calories in particular. You can't have excessive intake of vitamins and minerals. This can give rise to various types of toxicities, but these usually only occur if you're eating very strange diets or like overdosing on megadosing on vitamins and like that. So they're fairly rare. Mostly when we talk about overnutrition, we're talking about excess consumption of carbohydrates, fats, and proteins. And the main effect of this is to lead to obesity. Recent estimates show that the proportion of adults across the world who are obese

has increased from about 12% in 2012 to about 16% in 2022. So obesity is increasing pretty much in every country around the world, even in many developing countries, which still have problems of undernutrition are increasingly facing what's sometimes called a double burden of still high levels of undernutrition alongside increasing levels of obesity. Nevertheless, developing countries in Asia and Africa still have fairly low rates of obesity, but increasing. Rates are higher in the Middle East and the Americas and Eastern Europe. The United States has the highest obesity of any large country in the world, at 43%, so that's 43% of all adults in the US are obese. The Pacific region has the very highest obesity rate in the world, but the countries are relatively small, hence I said the US

has the highest obesity rate of large countries. Tonga, Nauru, Tuvalu, and Samoa all have above 50% adult obesity rates. It seems to be a combination of genetic predisposition and cultural factors that lead to very high obesity in the Pacific region. Obesity is a major cause of disability worldwide and is associated with a wide range of diseases, including cardiovascular diseases, type 2 diabetes, sleep apnea, certain types of cancer and osteoarthritis. So it's a very serious issue. It requires a whole episode to itself, so I won't say anything more about it here. I just wanted to mention it as a kind of an aspect of malnutrition that needs to be considered alongside undernutrition as sort of different poles representing an inappropriate balance of nutrients in the diet.

All right, the final section for today's episode, we're going to talk about metabolic rate. so far we've talked about different types of human nutrients and we've talked then about what happens when you get either insufficient or excessive nutrients so that's malnutrition now we're going to look at the kind of how much energy do we actually need like caloric intake and how this is determined particularly i'm going to talk about basal metabolic rate the basal metabolic rate is the rate of energy expenditure per unit of time as often this is measured like per day by animals that are endothermic so like mammals we increase our body temperature over that of the environment and that requires a great deal of energy. I mean, there's many other things that we need

energy for our body to function, to breathe, to circulate our blood, controlling body temperature, as I said, is a very big one, to produce new proteins, grow cells for our brain to function, contract muscles, all of that sort of stuff. So pretty much anything that we do like that, it requires energy. And the basal metabolic rate refers to the rate of energy usage that occurs for a given person when that person is at rest. So not engaging in physical, activity. The reason this is important is because we can kind of distinguish between calories that are consumed in the process of doing exercise, like physical activity, and calories that are consumed in the process of just essentially being alive, just functioning, just existing.

And the latter is the basal metabolic rate. It's incredibly important because it accounts for about 70% of the daily calorie expenditure for most individuals. Obviously, that will depend on how active you are, so if you're more active, it'll be a bit lower than that. And if you'll active, it'll be a bit higher. But it actually doesn't differ by that much. So physical activity, unless you go to absolute extremes, like exercising all day, physical activity doesn't actually affect, it doesn't actually change the amount of calories you need by that much, because it's only a small proportion relative to the basal metabolic rate. I'll discuss this in more detail when we do an episode on exercise. So 70%, as I said, is the basal metabolic rate, basic bodily functions. About

20% goes to physical activity and another 10% is used in digesting food. So that's thermogenesis. Now, one of the interesting questions that is sometimes raised about basal metabolic rate is how much does it vary across people? Obviously, not everyone has the same caloric requirements, even, again, putting aside exercise, so we're just talking about the basal metabolic rate here. One thing that's sort of fairly intuitive and is well known is that basal metabolic rate varies depending on your body size. So bigger and taller people have a higher basal metabolic rate than smaller and shorter people. That's basically because they have more metabolic requirements. They either have more cells or they have bigger cells, larger fat deposits, which require,

which have metabolic requirements, bigger muscles to move around. Their heart has to pump more vigorously to push the blood further on the body and so forth. So, you know, everything's bigger, it takes more energy, right? One of the better studies that I found looking at this, This was a 2005 cross-sectional study of 150 adults from Scotland in the United Kingdom. The number here is relatively small, but it's very expensive to measure someone's basal metabolic rate. You have to essentially hook them up to a breathing apparatus that measures the actual choleric expenditure, and it's a whole ordeal. So it's difficult to do this in a very controlled way.

And this study, I think, did quite a good job, and in particular it parceled out the variation that was observed in the basal metabolic. rate between participants into different causes. Like what is the reason why we see this amount of variation in the basal metabolic rate, which I think was sort of interesting. So just the raw data, across their 150 adults, so just looking at adults here, they found a minimum basal metabolic rate of 4,300 kilojoules per day. So this is in joules, not kilo calories, bear in mind, and a maximum of 10,500. So that's a very large difference. That's more than a factor of two difference between the person who had the smallest requirements and the largest requirements.

The average was about 6,300 kilojoules per day. Remember, this is not total energy requirements. This is just basal metabolic rate. You may be familiar, but that the average energy requirements of an adult is usually given as 8,700. So that's the total requirements. Here we're just talking about the basal metabolic rate. So it's about 70% that number. Based on these numbers, you might think, well, there's a very large difference in basal metabolic rate between people.

like it's more than a factor of two difference between the largest and the smallest, which is true. However, remember that much of this is accounted for by differences in body mass. So what they found is that 63% of the variation between people in their basal metabolic rate was explained by the fat-free mass. So basically this is how tall you are and to an extent how muscular. But I think most of this effect is just like size. Another 7% was explained by the fat mass. So if you have larger fat deposits, that increases your metabolic rate. You need to sort of metabolically service all of the excess fat deposits.

So you add those together, and about 70% of the variation in basal metabolic rate was explained by body mass and composition. Another 2% was explained by age, so it's well known that metabolic rate goes down somewhat over as you get older. It's not a huge effect, but it's still important. So that means that if we control for age and body mass and just look at sort of the pure different, between people like picking a person of the same size and the same age, basal metabolic rate varies between about 5,700 kilojoules per day and 6,900 kilojoules per day. So 95% of the population will be between about 5,700 and 6,900, which is a difference of about 10% from on either side of the mean. So this is interesting because I think it illustrates that

despite what some people say, genetic-based differences in metabolic rates do not result in very large differences in metabolism, at least when you control for body mass. Again, if you're much bigger than someone else, then obviously there's going to be a big difference. But just looking, like controlling for that and just looking at sort of pure difference per unit of body size, the difference is relatively modest, only about 10%. Now, this probably understates the total variation because this is only from a population of adults in Scotland. So that's probably more genetically homogenous than populations elsewhere, where there'd be more of a variation. But even so, it seems like the variation across people in basal metabolic rate when controlling for body size and age

is relatively modest on the order of perhaps 10, 15% on either side for the majority of people. So, you know, that's important, but it's not exactly huge. Another thing that I wanted to mention about basal metabolic rate is that not only does it vary based on body size, which we know about, and also age, which I've just discussed, but it's also affected by caloric restriction. So a number of studies have found that when you, if you go from eating, an adequate diet to maintain your weight, like whatever your weight is, you eat enough calories just to maintain that weight, and then you restrict from that, what happens is your basal metabolic rate actually declines. So a number of studies have looked at this, and there's different ways to

measure it, but it seems like a 25% caloric reduction, which is a fairly large reduction, but like not absurdly large, results in a 5 to 7% reduction in basal metabolic rate controlling for the reduction caused by the weight loss itself over a period of 6 to 20% reduction. 24 months. So in other words, if you engage in caloric restriction, you're going to lose weight, and that will reduce your metabolic rate, right? But even the point is even controlling for that, your basal metabolic rate adjusting for body size will also go down. It will go down by more than just the weight you've lost. And for a 25% reduction, the average amount is 5% to 7%. So this appears to be a metabolic response of the body to try to maintain the current weight.

and this is sometimes what people talk about when they say sort of vague things like that your body wants to hold onto its fat or like it resists a loss in weight because there is a metabolic response to caloric restriction people have also looked at whether increases in exercise have the same effect and it seems like the evidence is a bit mixed here but it seems like that it does not if you if you keep your caloric intake the same but increase your exercise then it doesn't seem like this does have the same effect of reducing basal metabolic rate, which is interesting. It's less clear why that might be. I think that more research is needed here. Greater muscle mass does increase metabolic requirements somewhat. So if you have more like skeletal

muscle, you know, you lift weights and things like that, then that in and of itself does lead to a slight increase in metabolic requirements. But the rate is fairly small. I think it's on the order of a few percent, even for fairly large amounts of muscle mass. But the exercise itself doesn't really seem to have much of an effect on the basal metabolic rate. Again, controlling for the body size. So it might seem from looking at this that, oh, increasing exercise might be a good way to lose weight because it doesn't have this effect of reducing basal metabolic rate, which means you'll have to cut your intake even further to obtain the given amount of weight loss. But it seems that that's actually not true, at least not if you just do the increases

in exercise, because the body also has regulatory processes that lead to an increase in caloric intake, which pretty much exactly offsets any increase in exercise that you do. So if you start exercising more, you'll naturally tend to just eat more and maintain the same weight. So you really need to pair exercise with caloric restriction, or at least not increasing your caloric intake in order for weight loss to be effective. But anyway, I will discuss these aspects of exercise and dieting and so forth in a future episode. That's not really the focus here, but I just wanted to kind of introduce and discuss basal metabolic rates as an important

component of nutrition. So that brings us to the conclusion of this episode today. We've talked about the key human nutrients. We've talked about malnutrition and we've talked about basal metabolic rate. In future episodes, I will discuss comparative diets and the science and effectiveness of those. We'll also discuss the effects of obesity in more detail and metabolic syndrome and cardiovascular health. And I want to do an episode also looking at exercise and the science of that. So those will come in due course. I don't know exactly when, but stay tuned for those. If you found the episode interesting, please consider supporting the podcast by leaving a favorable review, or you could make a monetary contribution by becoming a Patreon supporter, or making a one-off donation via PayPal.

If you would like to make a PayPal donation, or just send me a question or a comment or let me know how you listen to the show and what you get out of it, you can send me an email. My address is FOD12 at gmail.com. That's FODS-12 at gmail.com. Thanks. very much for listening and I'll talk to you next time.