Life Kit - The science of losing weight

Episode Date: January 5, 2026

When it comes to weight loss, there are many misconceptions about what works. So if you want to lose weight this year, here's what the science says about the potential health benefits, GLP-1 drugs, exercise and more.Sign up for Life Kit's Guide to Building Strength here: npr.org/strongerFollow us on Instagram: @nprlifekitSign up for our newsletter here.Have an episode idea or feedback you want to share? Email us at [e-mail] the show and listen to it sponsor-free by signing up for Life Kit+ at plus.npr.org/lifekitLearn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy

Hey, it's Mariel. Before we start the show, let's play a little game. What helps you live longer, improves symptoms of depression and anxiety, cuts your risk of chronic illnesses, bolsters your immune system, strengthens your bones, and reduces chronic pain? Strength training. And that's not even a full list of all the benefits. To help you get started building muscle, we created a newsletter series. No experience necessary to get going. Sign up at npr.org slash stronger.

or find the link in the episode description. You're listening to LifeKit from NPR. There's something we don't talk about much on LifeKit, and that's weight loss. There are a lot of reasons for that. One is, it feels like conversations around health and fitness can focus too much on losing weight, when our physical health is more complicated than that. Also, this show is about a life well-lived, and there's so much more to that than how many pounds you weigh or how your body looks. That said, we felt like this was the time to talk about it again.

Losing weight is a very common New Year's resolution, but it's complicated, and there are a lot of misconceptions about it. For instance, often people think that, you know, if they just can make some lifestyle changes, some hacks of their metabolism or something like that for a period of time, They can reach some goal weight that they might set out for themselves, and then they can relax after that. And I think that what most people need to realize is that that's not how weight loss works. If you want to maintain the weight that you might end up losing, then you're going to have to incorporate those lifestyle changes permanently into your everyday life. This is Kevin Hall.

He's a nutrition and metabolism researcher, formerly at the NIH. He studies weight loss specifically. And he says another thing people tie strongly to weight loss is exercise. Oftentimes people will start an exercise program around the beginning of the year and join a jam or something like that or hire a personal trainer. And because they've so tied the idea that one of the benefits of exercise is weight loss, and for some people it might be, others will get very discouraged if they don't see the numbers on the scales move.

And they might actually start quitting the exercise program, which would actually have independent benefits for all sorts of exercise. aspects of health, regardless of whether or not it affects your body weight at all. As we talk about all the time on the show, we need to move our bodies regardless of what we weigh. On this episode of Life Kit, I talked to Kevin about the realities of losing weight. If that's a goal for you, we're going to give you some facts to consider and takeaways based on the research. Kevin, this is a time of year when a lot of people are.

are thinking about weight loss. But before someone pursues that, who benefits from losing weight? Nowadays, given that there's such a high degree of prevalence of overweight and obesity in this country, I would say the vast majority of people can benefit clinically from losing a little bit of weight. For some people, that doesn't require much weight loss, maybe even 5% body weight loss. For others, it might require more weight loss to receive the very large benefits that people would, obesity often see with weight loss. But it's important to realize that just by looking at somebody, you cannot tell whether or not they are experiencing the metabolic side effects of having excess

body fat. That can kind of kick in at various different body sizes. And some of these body size doesn't necessarily tell you anything about their health status. But the vast majority of people who end up losing some weight will see some metabolic benefits. And when we say metabolic benefits, What does that actually mean? It means that they'll improve their glucose control. They'll improve their blood lipid levels, which are related to cardiovascular disease. Many aspects of several forms of cancer have been related to excess body fat, and so decreasing body fat can result in decreasing risk for various forms of cancer, but mostly these sorts

of metabolic diseases like heart disease, stroke, diabetes, and things like that. How clear is the research that it's weight loss or gain that matters here? Yeah, no, it's a great question. And for some outcomes, it's much more clear than others, right? So for some outcomes like type 2 diabetes, which is causally related to your body's ability to use the hormone insulin and whether or not your body is making enough insulin, that sort of process and the sort of pathophysiology by which diabetes develops and insulin resistance develops is becoming more and more clear. And it seems like excess body fat in the wrong

places, in other words, in organs like the liver or the muscle or around your pancreas, is causally related to the sort of progression of this metabolic disease and the development of type 2 diabetes. And so the ability to kind of remove fat from those locations, and unfortunately there's no targeted way to do that right now. It means you sort of have to remove fat from the entire body. Takeaway one, there can be real health benefits to losing weight. Though, as Kevin said earlier, you don't need to lose a lot of it to start seeing some of those benefits.

We're talking about 5% of your body weight. I asked him more about this. Okay, so let's say you're 220 pounds and you lose 11 pounds. That could be plenty to get the metabolic benefits we're talking about. Well, you could begin to see some of the metabolic benefits. Yeah, I mean, I think the point is that it depends on where you're starting and it depends on your level of disease to begin with. And obesity is now considered a disease in its own right. So it's not just increasing the risk of other diseases. That 5% weight loss, you can already begin to see some of those metabolic benefits in improving insulin resistance, for example. But of course, it is dose dependent. So in other words, the more weight that people lose, especially when you're starting off with very high amounts of body fat, the more metabolic benefits you'd tend to see. I mean, that makes sense. I just am cautious of telling people, you know, the more and more weight you lose, the healthier you'll be, because at a certain point, they're going to be tipping

into potentially eating disorder category or someone who's just like not getting the nutrients that they need, for instance, right? Right. No, I think it's really important that people personally this sort of discussion, right? I've been focusing on folks who clearly have excess body fat and can stand to lose quite a bit of weight as a result of that and see these benefits, but you're absolutely right. One of the challenges with discussing weight loss and discussing obesity in general is that there's a huge sort of societal and stigmatizing notion about people with obesity and people with excess weight. And there's also this cosmetic aspect, right, this pressure to look a certain way, which you don't get with other diseases like type 1 diabetes, for example. It's not associated with

anything that you can observe from the outside. So I think you're right in pointing out that there are other factors at work here when we're talking about weight loss, both in terms of people with obesity, receiving the sort of stigma from the medical establishment even, as well as, you know, everyday folks, and just the risks of conflating many of the cosmetic benefits that people believe they're experiencing when they're losing weight with the health benefits. And then you're right to point out the risks of people developing potentially disordered eating behaviors as well, which is obviously problematic. It sounds like something to check in with a doctor you trust about like a healthy target for you. Absolutely. You've mentioned losing body

fat or carrying around excess body fat, as opposed to weight specifically. I wonder, how are those things different? Yeah, no, it's a great question because obviously body size differs between people quite a lot, just looking at height. And people who are taller, obviously, typically way more as well. And so one of the questions is what is your body composed of? How much of your body is muscle mass, for example. How much of it is fluid? How much of it is these various different organs and how much of it is body fat, which can be stored in healthy places and can be stored in places that are not so healthy and cause some of these adverse metabolic consequences. So yeah, what your body is made out of and in your particular body fat level and where you're carrying your

body fat can be very important to know when it comes to risk of these different metabolic complications. Are there reliable ways to measure body fat? And is that worth doing? There are reliable ways. They end up being relatively expensive for many people and not all that well available. So most people will use this simple measurement of their weight divided by their height squared. And that's the so-called body mass index. And it's correlated quite well with body fat for many people. But there are exceptions and there's still quite a bit of uncertainty about that. that. And the other thing that's important to know, too, is that even people who do end up having high levels of body fat, where that fat is being stored in the body, is it being stored in places which are more or less inert and are not affecting health very much, or are they being stored in places that are more metabolically dangerous, your total body fat measurement will not tell you much about that. That's why some physicians are now starting to use things like the waist to hip

ratio. If your waist is much, much larger than it should be for your hip measurements, that means that you're probably carrying quite a bit of fat around your abdomen and, in particular, your liver, which might be more metabolically dangerous than carrying it on your thighs, for example. And I imagine you can also be considered at a healthy BMI or at a healthy weight, according to your doctor, but then you have high cholesterol. or high lipid count specifically, or you develop type 2 diabetes. And so I feel like that's important to point out.

That's exactly right. And it turns out that, you know, different ethnicities have different sort of BMI thresholds, which people talk about as being particularly risky. So men, especially from South Asian descent, will look perfectly fine from a BMI perspective, but at a much lower BMI, they will generally start to see these increased risks.

and that seems to be because they're storing quite a bit of their fat in their visceral organs and their liver in particular. So, yeah, so just looking at the scale on its own is probably not sufficient. And even just looking at the scale with your height, factored in with BMI probably isn't sufficient either. You do have to kind of look under the hood, so to speak, and make sure that your metabolic health is aligning with your so-called healthy BMI. takeaway two weight is not a cut and dry indication of health someone with a lot of muscle can weigh the same as someone with a lot of body fat and have very different health outcomes also it can make a difference where your body fat is stored for instance if you carry a lot of weight around your liver that might be more risky to your metabolic health than carrying it on your thighs one common screening tool that doctors use to estimate body fat is bMI body mass index It's simply your weight divided by your height squared.

BMI was developed by a statistician in the 1800s and used in population studies to analyze data about men. It was later adopted by the insurance industry to assess risk. Now you'll find it on almost all of your medical records, even though it is a highly imperfect measurement and it doesn't take into account muscle mass, bone, or where your fat is stored. Researchers have been looking for a more reliable metric. A person's waist to hip ratio is one. one promising measure. And another is BIA. That's a type of analysis that uses an electrical current to estimate body fat. There are scales that do this and cost a few hundred dollars. One other reminder, even if you are considered healthy according to your BMI, you can still

have conditions like high cholesterol, diabetes, and heart disease. So it's important to get routine physicals and screenings anyway. We'll have more Life Kit after the break. The conversation around weight loss has shifted a lot in the past few years with OZempic and other drugs like it. I wonder what are your thoughts on these drugs and who do they work for? That's right. I mean, in the past, we had lifestyle interventions that have led to modest amounts of weight loss. And like I said, some benefits for many, many people. But there are others that could benefit from more weight loss, but we're not achieving that benefit because it just turns out.

to be so darn hard for folks to kind of incorporate major changes into their everyday lifestyles. And then there's the bariatric surgeries where we've seen, you know, huge amounts of weight loss and in these large benefits. But of course, it's a pretty dramatic procedure to undergo. It's expensive. Sometimes you will qualify for it through insurance, but it's a major thing. And so it's also had relatively limited uptake over the years. And this new class of weight loss medications now has offers something in between right offers the sort of 15 to 20 percent average body weight loss comes with many of the benefits of bariatric surgery but not to the same extent also tend to be quite expensive for many people to to obtain and they're not without risks in

some folks and side effects as well so the way I sort of see it is that there are certainly a welcome option for for many many people but of course it's not something that can be handed out like candy either it's uh needs to be under a watchful and uh well trained physician and unfortunately i think we see right now a lot of physicians who are not well trained necessarily in obesity management and uh we even see you know a lot of uh people getting these uh drugs with very little oversight and i think that's that can be quite worrying especially when they're not even using the brand names of some of these drugs there are these compounded drugs of sold by, you know, pharmacies, which are quite worrying for many physicians.

Takeaway three, GLP-1 drugs like OZempic, Wegovi, and Monjaro, can be helpful tools, especially if someone is trying to lose a lot of weight or they're at the point where they're also considering bariatric surgery. But like any other drug, they come with risks and side effects. You also need to keep taking them to keep the weight off. If you do start taking these drugs, make sure you're doing it under the supervision of a doctor who's well-versed in obesity men. management. What would you say are the most persistent myths in weight loss?

I think the most persistent myth when it comes to weight loss is still the idea that this is just a matter of willpower, that the reason why people have excess weight and excess body fat to begin with is some sort of moral failing. And if you just kind of were to make some simple changes in your life that you would be able to achieve a quote-unquote healthy weight, and it's because of some sort of moral failing that people have experienced excess body fat. And I think that that line of argument has been kind of demonstrated scientifically to be clearly false, that somewhere between 40 and 70 percent of the variation in body size is due to genetics. And in the past several decades, we've experienced a sort of shift in particular our food environment that has caused

the increased prevalence of these diet-related chronic diseases. And still, I think, many people feel like if there was people just took more personal responsibility that they could easily or maybe not easily, but they could well their way to a more healthy weight. And that's clearly not the case. I think you hear this a lot when people say, oh, it's just calories in versus calories out. Yeah, the idea that we had complete control over both of those variables, right? Both calorie intake and calorie expenditure, the number of calories our body is burning through metabolism and physical activity as well as other functions, those things are under biological control and often operating below our conscious awareness. And we know that many of the genes that are

kind of increasing the risk of obesity and things like that are genes that are genes that are are primarily expressed in our brains and are fundamentally related to appetite regulation. And so these are biological factors that we have very limited control over. Takeaway four, there's this idea that all you need to lose weight is willpower. But that's a misconception. A lot of the factors that contribute to our weight, including genetics, are out of our control. So if someone does want to lose weight, what are your top? tips based on the research?

I think focusing on weight alone might be a little bit of a mistake, right? I think that's better to focus on improving the healthy aspects of your lifestyle that you can fit into your lifestyle on a regular basis. And exercise is one of those top things that might not lead to very much weight loss in many people, but it's clearly going to have health benefits. Another aspect is just improving the overall quality of your diet, eating more fruits and vegetables and whole grains and legumes and things like that. like that and avoiding saturated fat and sodium and sugar and refined grains and ultra-processed foods

and those kinds of things, if you can kind of do that on a regular basis without spending too much money or having to prepare all these meals and you can actually have the interest in doing that and have the skills to do those things, that would be great. But again, on a case-by-case basis, many people are unwilling to make these huge changes just because they can't afford it. There's not enough time. They have competing pressures in their life. So there's lots of advice that you could give people, but the real trick is figuring out what types of advice to improve their overall lifestyle. Many of those things will lead to weight loss. Some of them won't lead to much weight loss, but they will all sort of improve people's health and how they feel. So I tend to

like to try to decouple those lifestyle changes that people should think about incorporating and keeping persistent throughout very, very long time periods from focusing on the number on the scale. Takeaway 5. Focusing solely on losing weight might not be the best resolution for you. Instead, if you're not already exercising regularly, start, incorporate strength training once or twice a week. Do some cardio.

The CDC recommends 150 minutes a week of moderate intensity movement like brisk walking or jogging, dancing, cycling, chasing your dog around, shoveling snow, whatever you like. Also, improve the quality of your diet, cut down on ultra-processed foods, and eat more fruits and vegetables. These things may or may not help you lose weight, but they'll definitely make you healthier. Kevin, thank you so much for this. For sure. My pleasure. All right, time for a recap.

Takeaway one. There can be real health benefits to losing weight, but you don't need to lose a lot of it to start seeing those benefits. We're talking about 5% of your body weight. For a 220-pound person, that would be 11 pounds. Takeaway two. One common screening tool that doctors use to estimate body fat is BMI, body mass index. It's simply your weight divided by your height squared. It is a highly imperfect measurement, and it doesn't take into account muscle mass, bone, or where your fat is stored.

Researchers have been looking for a more reliable metric. One option is looking at someone's waist-to-hip ratio and another, is using a scale that estimates body fat using an electrical current. Takeaway 3. GLP1 drugs can be helpful tools, but like any other drug, they come with risks and side effects. You also need to keep taking them to keep the weight off. Takeaway 4. There's this idea that all you need to lose weight is willpower. That is a misconception. And takeaway 5. Focusing solely on weight loss might not be the best goal for you. Instead, consider regular exercise, strength training, and cardio, and improving your

diet. These things may or may not help you lose weight, but they will definitely help your health overall. And that's our show. Hey, speaking of strength training, are you looking to get stronger this year? We have a special newsletter series to help you start your own strength routine. You can sign up at npr.org slash stronger. This episode of Life Kit was produced by Claire Marie Schneider. Jewel's editor is Beck Harlan, and our digital editor is Malika Garib. Megan Kane is our senior supervising editor, and Beth Donovan is our executive producer. Our production team also includes Andy Tagle, Lenin Sherburn, Margaret Serino, and Sylvie Douglas. Engineering support comes from Robert Rodriguez.

Fact-checking by Tyler Jones. I'm Mary El Cigara. Thanks for listening.