Science Vs - Hydration: Are You Drinking Enough Water?

Episode Date: July 25, 2024

[REBROADCAST] Celebs and wellness blogs treat water like a magic elixir that will make us the most attractive and healthiest version of ourselves. But do these claims hold water? And how much do we really need to be drinking to stay healthy? We speak to Professor Hollie Raynor, Professor Stavros Kavouras and Dr. Tamara Hew-Butler to find out. Find our transcript here: https://bit.ly/sciencevshydrationrerun  We’re doing an “Ask Wendy Anything” episode! To ask Wendy a question, get in touch on Instagram: Science_Vs; Tiktok: @wendyzukerman. If you want to send us a voicemail you can email us on [e-mail]. If you're in the US, you can call us at 774-481-1238. This episode was produced by Wendy Zukerman, with help from Nick DelRose, Michelle Dang, Meryl Horn, Courtney Gilbert, Rose Rimler and Disha Bhagat. Editing by Blythe Terrell with help from Caitlin Kenney. Fact checking by Diane Kelly. Mix and sound design by Sam Bair. Music written by Bumi Hidaka, Emma Munger, Bobby Lord, So Wylie and Peter Leonard. Thanks to the researchers we got in touch with for this episode, including Dr. Andrew Brown, Dr. Jason Lee Kai, Dr. Jodi Stookey, Dr. Vincent Ho, Dr. Tristan Struja, Dr. Stephen Goodall, Dr. Ekua Annobil, Professor Barbara Rolls and Dr. Krista Casazza. Special thanks to Rasha Aridi, Eric Mennel, The Zukerman Family and Joseph Lavelle Wilson. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Hi, I'm Wendy Zuckerman and you're listening to Science Faces. So right now we are busily researching for next season and I think it's going to be really great. We just had our first pitch meeting and as is obligatory, we talked about caca and testicles and of course a bunch of amazing science and I can't wait to share it with you. But while we are working on next season, we figured that it's kind of been a minute since you heard from us and we thought maybe you missed us. So we figured just over the next few weeks we'd put some fun stuff down our feed,

and one of those is going to be an ask me anything. Yeah. So you can ask me anything. I'm a bit nervous about it. The show's been going for ages and we've actually never done an episode like this. So if you have a question for me or anyone on the team, you can pop it on our Instagram, science underscore VS. You can send them to me on TikTok at Wendy Zuckerman. You can email us a voicemail. If you're in the US, there's a number to call. To get all those details, just look in our show notes.

So go for it. Ask me anything. But today, we are jumping back into one of our favourite episodes, and it's where we pit facts against fluids as we tackle hydration and ask how much water do you really need to drink to be the best and brightest you. It's been hot in the Northern Hemisphere, and when it's hot, people love to talk about staying hydrated. Not just to avoid heat stress, but for all kinds of reasons.

I got to chatting about this with producer Michelle Dang. Hey, hey, hey. Hello. I read her a typical article on why we need to stay hydrated. This one's from CNN. From bad breath to car accidents, dehydration is a real health threat. Car accidents. Exactly.

And then it says it dries your skin out. It makes you tired. It sours your mood. It constipates you. Mild dehydration may affect your ability to take on mental tasks. Like the constant focus on like mild dehydration, like just a little bit of dehydration, it could mess you up. Yeah, like it's an epidemic or something coming for us. And one way to fight this dehydration epidemic is to drink more and more water. It's as if you can't drink enough

water these days. I mean, forget the old eight glasses a day rule. There's this trend rolling around the internet, the gallon challenge. One gallon of water every day for at least a week. That's just under four litres. According to the gossip mags, Beyonce and Gwyneth Paltrow were into it. And the idea is that after drinking a gallon of water a day, your pounds will melt away and your skin will look smoother and healthier. Which Michelle was kind of up for.

Oh, ooh. All all those things I want. I want my skin to look better and I do want to lose weight. So Michelle and I decided to give it a go. So we'll see. This could be an exciting week. This might be life-changing. Today is the day the gallon challenge begins. We bought some very big bottles of water specifically designed for this challenge. Okay. There it is. Oh my gosh. Okay, so this bottle is a gallon. It's the size of a gallon.

It's about as big as my head, right? It looks bigger than your head. It's definitely bigger. Look at it. It's the size of a gallon. It's about as big as my head, right? It looks bigger than your head. It's definitely bigger. Look at it. It's longer. It's longer than your face. It's a lot of, it looks like a lot of water. I'm a bit shocked. The bottle has time stamps on it, basically a schedule to follow. And each one has a motivational message next to it to keep us going throughout the day. So at 7am, our water bottle says good morning. At 9am, you've got it. 11am, remember your goal.

1pm, that's it. 3pm, keep drinking. Oh, that one's ominous, isn't it? Keep drinking. 5pm, no excuses. 7pm, a little bit more 9 p.m. well done as we suck down all this water we are going to answer the following questions one can drinking lots of water help you lose weight two what exactly happens to us when we're dehydrated? Could it be messing with your mind and your focus? And three, how much water do you really need to drink each day?

Okay, I'm going to fill this up with water and we are going to begin Gallon Challenge. Gallon Challenge. Gallon Challenge. Gallon Challenge. Gallon Challenge. Gallon Challenge. Gallon Challenge! Gallon Challenge! Gallon Challenge! Gallon Challenge! Alright.

I'm taking my empty gallon bottle and filling it up with water. Science versus hydration coming up why is this so much water oh god okay kiara it means smart in italian too bad your barista can't spell it right so you just give We'll be right back. Is it too late to change your latte order? But with an espresso machine by KitchenAid, you wouldn't be thinking any of this because you could have just made your espresso at home. Shop now at KitchenAid.ca. Bumble knows it's hard to start conversations. Hey.

No, too basic. Hi there. Still no. What about hello, handsome? Who knew you could give yourself the ick? That's why Bumble is changing how you start conversations. You can now make the first move or not. With opening moves, you simply choose a question to be automatically sent to your matches.

Then sit back and let your matches start the chat. Download Bumble and try it for yourself. Holy s***. What does it tell me? Good morning. I've got this. First sip. How do people drink out of this?

Welcome back. Water is essential to life. Look in the mirror. Roughly half your body mass is water. But can drinking lots of it help you? The first thing we're going to slurp up is whether drinking water can help you lose weight. And this idea is huge. Sites like WebMD hail water as the secret weapon in weight loss.

And a national survey from the CDC found that drinking a lot of water is one of the most common ways that people try to lose weight. So to see if this idea holds water, I called up. So my name is Holly Rayner. Holly is a professor of nutrition at the University of Tennessee, Knoxville. She researches weight loss and diet, what works and what doesn't. And Holly told me that to a lot of people, it just kind of makes sense that filling your belly with water would help you lose weight. I think people go like, well, gee, I'm putting something into myself. You know, I'm going to feel a little bit fuller. Maybe I'm thirsty instead of hungry.

I'm not saying that we have evidence that supports that. Oh, no, no, no. We will get into that. All right. So let's get into that. The evidence. Holly says that there's actually been quite a lot of studies testing whether water can help you lose weight. Like, one study took almost 40 teenagers who were overweight or obese, encouraged half of them to drink more water, which they said they did, and then followed them for six months. At the end of the trial, the group drinking more water

didn't lose any more weight. Of course, that's just one study, but researchers have looked into this all kinds of ways. Like, they'll do these studies where they bring people into a lab, give them a big glass of water, and then put a bunch of food in front of them. Yes, yes, yes. Right, and you can very objectively measure

like how much the person eats in the meal, for example. Does it look like what they get is like an airplane, like a meal in the airplane? Is that... Yeah, yeah, yeah. Yeah, like that, like that. And basically, they're trying to see, did drinking that glass of water mean that people ate less?

Holly and a team of researchers pulled together a bunch of studies on this question, weighed it all up and concluded that there was quote, little evidence that drinking water with a meal can help you lose weight. It just doesn't look like drinking water during the day, drinking water before a meal. It does not at all look like that if you consciously go, oh, I'm hungry. So therefore, let me drink some water because that will help me feel full and I'm not going to eat as much. That doesn't seem to work that way. And Holly says that once you think about how digestion works, it actually makes perfect sense that you couldn't fool your body

into thinking that water is food. Food sits in your belly for a while because it needs to get digested. But water, it just doesn't hang around in the same way. It gets absorbed pretty fast. Water is more rapid than anything because there's nothing for the stomach to go like, well, I got to break this down. Like there's nothing to digest really. It's not like it just sits there for hours in your stomach. For example, if you drink two glasses of water, the majority of it will be out of your belly within 20 minutes. For solid food, that could take several hours.

So bottom line, drinking water is not some great weight loss drug. But curiously, if you are trying to lose weight, some research has found that if the water, instead of being in a glass beside your food, is actually inside your food, that might help you lose weight. So here's how one famous study from the 90s tested this out. They gave some people a glass of water to drink with a small portion of chicken casserole as an appetizer. I know, chicken casserole. It was the dieties, all the rage.

Another group got the casserole, but this time the glass of water was kind of poured on top of it. It was prepared as a chicken casserole soup. Everyone gobbled up their apps, and then the researchers carefully measured how much each group ate afterwards for the main course. It turned out that the people who'd had the casserole soup, well, they ended up eating less at their main meal, about 100 calories less.

Now, Holly says this isn't a watertight formula for weight loss, but there is a group of studies suggesting that when food is packed with water, we might end up eating fewer calories overall. And it doesn't have to be a weird casserole soup. It could be cucumbers, leafy greens, or watermelon. Actually, watermelon is a great one. Told you. One thing that might be going on here is that water adds volume to food, but it doesn't add calories.

And so that means that waterlogged food can look pretty big on a plate without being that many calories. And this might have a psychological effect on us where we think we're eating more. Think about a handful of raisins versus a bowl full of grapes. Where it's like, wow, look at all this food that I get to eat. Oh, I'm still chewing. You're probably, you know, feeling a little bit fuller. So bottom line, there is some evidence that water inside a meal might help you eat less calories.

But outside the meal, in a glass or a giant gallon bottle, the evidence ain't so crash hot. Still though, before we leave this whole idea in the dust, Holly told me that there is one instance where drinking water does help us lose weight. And that's this. If you're drinking water instead of, say, some sugary drink. Soda, juice, coffee drinks that, you know, have a lot of calories in them. Like a frappe with cream and all that good stuff. Yes, that makes perfect sense. You're literally drinking less calories. have a lot of calories in them. Like a frappe with cream and all that good stuff. Yes. That makes perfect sense. You're literally drinking less calories. Yeah. So, so you probably, as

you're drinking a lot of your water here, you're probably not drinking other beverages. You're absolutely right. I was like, oh, I might get some juice for lunch. Then I was like, uh-uh, all that liquid is going to come from this gallon. Right, right, right. So if you had water instead of juice, obviously then that means that you consumed less energy generally. All right. Bottle you can stick by me for today. See, it's not all for naught.

With our gallon bottles sticking beside us all day, Michelle and I made it through the first day of our gallon challenge. I did it. I did it. I'm proud and I'm bloated. I'm proud and I'm blo to eat a pizza. Hello, hello, hello. Okay, it is day two of the gallon challenge. The virgin sip of the day. Not refreshing. It is 11am.

I am at 11am on my bottle. Remember your goal, it says ominously. I haven't felt like drinking, but I guess I just need to tell myself. I need to read the messages. I remember, Michael. So, on to this idea that water is an amazing miracle drug, that it can help our skin, digestion and brains work better. Is any of that true? Well, for this, we need someone who doesn't need motivational phrases

to help them drink water. I like to drink water. I get an immense pleasure from drinking water. Professor Stavros Kourouris is at Arizona State University, and he's researching whether people can benefit from drinking more water. And so, to understand the claims out there about the power of water, let's find out what happens to us as we get dehydrated. And Stavros, he often puts his hand up to volunteer for dehydration experiments. In one that he told me about, he had to do exercise for a few hours

and then go to sleep with basically no water. When he got up, all he wanted was a big drink. But instead, he just got this dry-ass sandwich. And I remember having the bread stuck in my mouth and I was like, my mouth was super dry. And I could not chew it. And I remember I finished my meal and then I took a sour and I was like rinsing my mouth with water and the sour. Is that cheating though? Is that cheating?

I didn't drink it. I wasn't drinking it. And when we're talking about what happens in our body as we get dehydrated, having a dry mouth is one of the first signs that you need to drink water. You'll also get thirsty. And if you don't get to water soon, things can just go downhill from there. To keep your vital organs filled with the fluids that they need, your body will actually start to steal water from other places, like your blood. So your entire blood volume shrinks.

So when it shrinks, your blood becomes thicker and your heart has to work harder. One small study in cyclists saw that after they were riding for roughly an hour without drinking water, their blood volume had dropped compared to when they were allowed to drink. And as your heart is pumping harder and harder, you can start to feel tired, and doing any kind of exercise can become really hard. Speaking of hard, your poo also becomes a victim to water loss. Your turds get all hard like a wombat and can get a bit constipated. But what happens when you push this even further and get people super dehydrated?

Well, Stavros told me about this study from back in the 1940s. Researchers took a squad of 20 soldiers and got them to walk in the Californian desert for hours. The researchers described the landscape with scurrying lizards, where the mountains are painted in sunrise and sunset colours. But these soldiers, they couldn't really enjoy it. It was over 100 degrees Fahrenheit. That's more than 40 Celsius. And they weren't allowed to drink anything.

Not a drop. Not surprisingly, the soldiers didn't fare well. Stavros and I read some lines from the study together. It says two men were observed to become exhausted and somewhat hysterical. At least one man opened a cactus and chewed it. P and R, which I suppose were people in the study, P and R, threatened to quit unless given water. G tells R to shut up and let us suffer in peace. If you don't give me some water, I'm going to quit. Yeah, this line about like the skin shrivels and shrinks against the bones. The eyes become sunken. Vision is dim.

Those are extreme, extreme cases, but it does make sense. It makes sense because as your body gets more and more desperate, it starts to grab water from wherever it can, like your skin. Usually your skin is like an elastic band. If you pinch the back of your hand, it should snap right back. But if you don't have enough water, your skin won't bounce back. It'll just kind of sag. And when you are really dehydrated, even your eyeballs get water sucked out of them. And the change in the volume of your eyeball can impact your vision. How is the brain getting affected as you keep pushing dehydration to its limits?

So you lose water from the brain and it becomes a little bit smaller. Wow. Parts of your brain, if you're dehydrated enough, can literally get smaller. That's correct. Yes. We know that some areas shrink. So in some ways, what the wellness blogs say is true. When you really, really don't have enough water, your skin can look thinner and sag, your digestion slows down, and it can affect you mentally. But the big question is, how dehydrated do you have to be for all these effects to kick in? Because according to the news, it looks like being just a little dehydrated can lead to muddled thinking and brain fog. Is that true? Well, to understand that, you really need to know what it means to be dehydrated in science land.

Many studies looking at this define it as being what's called 2% dehydrated, which means you, say, do some exercise and sweat so much that you lose 2% of your body weight in water. Studies have found that it takes something like walking in the heat for an hour and a half or rowing on a rowing machine super hard for an hour without drinking any water to lose 2% of your body weight. I talked to Stavros about this.

So do people lose that much from day to day? And the answer is probably not. Right. Like if you're sitting in an office. You probably won't lose that much. Right. You won't lose that much sitting in the office. And from the studies we looked at at Science Versus, we think this is true for a lot of the claims around dehydration. The research is often talking about what happens when you lose quite a lot of water.

And the funny thing is that if your brain firing on all cylinders is your main concern here, the nerds have actually looked at what happens when people hit this 2% dehydration mark. They've done cognitive tests on them. And even then, they don't always see effects. Leading one review paper to say that many of us would probably need to be even more dehydrated than that before our brain goes bung. And as I was drowning in research on this one, I did find some studies that showed being a little bit dehydrated

might affect your cognition. But when I spoke to researchers about it, they said that this might not be some magical thing about water. It could just be that you're a bit distracted. Your brain is like, I'm thirsty. I want to drink a water. Let me drink some water. I'm thirsty.

Come on, let's drink some water. Why are we doing this cognitive test? I want some water. I want some water. That is distracting. Kind of like if you're hungry, you might not do so well on a math test. And as for me and Michelle, with our gallon challenge,

we didn't feel like our brains were any sharper. I don't think I'm more focused. I don't think so. I don't think it improved anything with my focus or I don't think it improved anything with memory. So far, this gallon challenge does not seem to be living up to its promise. It's not going to make me lose weight or feel more on top of things mentally. And by Tuesday night, both of us were pretty over it. A friend, Eric, came over to my place and I was not happy. How does it feel? It feels like drudgery.

Do these work? The, like, good morning, you've got it, remember? No, it's like... Is it frustrating? It's frustrating and it's like... My least favourite is 11am, remember your goal. It's like, f*** you. F*** your goals.

7 p.m. I also despise. A little bit more. It's actually a f***load more. To be honest, I'm just very slowly not happening anymore. Just like the feeling of this can't go any further. I'm not going to push it. It's almost 10. I have like the tiniest bit left to go.

I'm so fucking bloated. And I'm like gassy. I don't know if it's something I ate. It's like a big bubble. That felt better. Day two, finished. After the break, it turns out there's an app that you need to stay properly hydrated.

Am I going to tell you all about it? Chiara. It means smart in Italian. Too bad your barista can't spell it right. So you just give a fake name. Your cafe name. Julia. But the more you use it,

the more it feels like you're in witness protection. Wait a minute. What kind of espresso drinks does Julia like anyway? Is it too late to change your latte order? But with an espresso machine by KitchenAid, you wouldn't be thinking any of this because you could have just made your espresso at home. Shop now at KitchenAid.ca. Metrolinks and Crosslx are reminding everyone to be careful

as Eglinton Crosstown LRT train testing is in progress. Please be alert as trains can pass at any time on the tracks. Remember to follow all traffic signals. Be careful along our tracks and only make left turns where it's safe to do so. Be alert, be aware, and stay safe. Welcome back. Today, we're getting our willies wet on the science of hydration. Michelle and I sailed through Wednesday. It is day three of drinking water. Here's to glass one.

Done. Yeah, I did it. I did it. Two more days. And now it's time to meet our final guest for today. It's someone who gets very, very annoyed by all the messaging around, you need to drink more water. It's Dr. Tammy Hugh Butler at Wayne State University in Detroit.

And she hears this all the time. Recently, she was at the doctor and a nurse told her, You know, you just need to drink a lot of water. That's going to solve all your problems. It's going to stop your blood pressure and you're not going to get any headaches and your digestion is going to be fine. You just need to drink more water. And for her, I was just like, I'm like, that's not true. The reason she says that's not true is because our body has a

badass way of making sure that we have just the right amount of water that we need. And it all comes down to this particular balance between water and salt, which affects so much, like even the size of the cells in our body. So if you lose too much water and you concentrate the salt, all of your cells shrink like raisins. So your body doesn't like that. It doesn't function well when you're all shoveled up.

When you get dehydrated, the water flows out of your cells, so they literally get smaller. On the other hand, say you drink too much water. The water is going to flow inside of your cells and all of your cells are going to swell. Your body doesn't like that either. And this might be why people think that drinking a ton of water could help their skin look pretty. Because if it's swollen, maybe it looks like it has less wrinkles. But Tammy's like, if this is doing anything noticeable, it's not going to last.

Because your body has evolved all of these processes to regulate all of this and to not keep you all blown up for long. Because your body's like, I don't want to swell. I don't function well swelling. So to stop your cells from swelling or shriveling up, here's how your body tracks all this, starting with what's in your brain. We have sensors that are built into our brain and they're always like sampling. They're like licking the blood that goes through the circulation. These specialized sensors that are licking your blood are called osmoreceptors. And if you've

drunk too much water, they're going to be like, Like, it's not salty enough. Those senses send a message that gets relayed to your kidneys, which tells them, we don't need this water. And your kidneys, which are filtering your blood, will pull out that excess water and ditch it, so you pee it out. On the flip side, if you're low on water, say dehydrated, those senses are like, Ooh, too you're low on water, say dehydrated, those senses are like, ooh, too salty, I need water.

And so that's when you get thirsty. Your body also sends a hormone, antidiuretic hormone, basically telling the kidneys, hold on to the water. And Tammy says that this happens really fast. That activates your kidney within 40 seconds. Like within a minute, your kidney's like, oh, I need this water. And how your kidneys are going to keep this water, it's actually super cool. You can think about it like this. There's this giant network of straws, or water channels, in these particular cells in your kidneys, And they suck up the water so that it stays in your body. One single cell has 12 million of these straws.

So if you think about all the cells, I mean, there's like billions of these like straw armies that serve to like suck up the water when your body needs it. And you don't have to think anything about it. It's amazing. You know, whatever you do, drink eight glasses, drink 20 glasses, it's going to correct for that because it wants to keep you alive. So that's why we have kidneys. Oh, that's so cool. It's so cool. It is.

So perfectly tuned, you know. Well, because water, I mean, water is necessary for life. So we're like, oh, you know, you need to drink this much. You know, there's an app and I got a water bottle that's going to ring, you know, to remind me to drink. That's all gimmick. You have these apps inside your brain and nothing's going to be better than that. And during the gallon challenge, Michelle and I became very acquainted with this app in our brain because it was constantly screaming, release the water. Gotta pee. The pee is here. Gotta pee again. Do you know what time it is? It's time to pee. Michelle, I just have to, I just have to pee. I have to pee.

All right, let me go find out what color my pee is. I'm having trouble concentrating. Okay, first meeting interrupted by pee. It was a pale yellow. It's like, the inside of a banana. Someone's in the bathroom. Someone's in the bathroom. So, at least we know we have functioning kidneys. Okay, here's where we're at.

Our bodies are amazing. For most of us, our bodies will tell us how much water we need. We'll pee out the excess, and if we don't drink enough, it'll help balance that out too. And when your body does need water, it'll take that water from wherever it can. That apple you had for breakfast? Great.

The soup you had for breakfast? Great. The soup you had for lunch? Perfect. Even that jello that you ate at a kid's birthday party? Also wonderful. And you don't need fancy waters either. Tammy says that Gatorade is basically like drinking flavoured water. And when it comes to the latest trend, alkaline water. There's just so little research on that. There's nothing magical about alkaline, mineral, bubbly. That's nonsense. That's totally, that's, you know, it's trying to sell you something.

It's trying to sell you something that you don't need. You know, even to the alkaline water, well, what's your stomach? Acid. So, you know So you start drinking that. It just neutralizes it. There's no health benefit once it gets into your body. Because your body, it just wants H2O. That's what our body wants. Yeah. So your body doesn't care where it comes from. It's like, oh, I only want plain water. It just wants the fluid. I mean, people are like, well, how much water do you drink? I drink a pot of coffee, you know, in the morning and yeah. Yeah. Even coffee counts as water. The research shows

that if you're regularly downing coffee or tea, caffeine doesn't dehydrate you or make you want to pee more. So in these studies. Caffeine itself was not a diuretic. Oh, that is interesting. So the reason that you pee more when you drink coffee is literally just because you're drinking like water in the coffee. Yeah. Yes. Coffee does make you poo though, right? It does. Yeah, it does. Yeah. So the morning, like that, that's something different. Okay, okay. Okay, so the last thing we want to look at today is this. If you like to drink heaps and heaps of water, you like doing the gallon challenge, downing buckets of this stuff,

and you feel like it makes you a better you, then why not keep going? Look, it's probably totally fine, but there is something to watch out for. You can overhydrate, and in very, very, very rare cases, people can die. This is actually how Tammy got interested in studying hydration. She used to be a podiatrist, and about two decades ago, she was volunteering in the medical center at a big marathon.

I was working on, I was popping blisters, you know, pulling the black toenails off. Anyway, so I'm watching. And then forerunners actually started to have seizures in the medical tent, and then they were taken to the hospital, and four of them were in comas for a week, and they almost died. And back then, we had no idea what caused it. It was horrifying.

Tammy dove into the research, and she found out that when you drink way too much water, the cells in your body do that swelling thing that we talked about, and the cells in your brain swell too. And so if you think about it, your brain is like swelling, swelling, swelling. There's no room for the brain to get any bigger. It runs into the skull. Your skull is just going to like, it's not going to move. And it pushes your brainstem out. And that's how you die. It pushes your brainstem out of your skull. Yeah, and that's it.

Done. The risk of dying is low, but it's completely preventable. You just don't need to drink that much fluid, particularly when you exercise. Tammy and her colleagues worked out that athletes are at a higher risk of this because when you exercise, your body tries to conserve water so you don't pee out as much, which can mean that if you're drinking a ton, it can build and build and build. But you really got to drink a lot of water for this. Tammy says as a rough estimate, don't drink a gallon of water in less than an hour. And Michelle and I, we were not drinking that fast. But weirdly, on day four of the gallon challenge, I was feeling a little strange.

I just have a bit of a headache. Ah, is the problem. And I'm wondering if it's from the water. It sort of feels like I would have thought it was dehydration but it couldn't be this is stupid okay I'm so close get it day four Get it. Day four. Ugh. Could I have possibly been like over-hydrating?

Yeah. Yeah. The symptoms are exactly the same. You can get a headache from dehydration, but you can get, I mean, one of our first signals for over-hydration is a headache because your brain starts to swell. So now that you've well and truly scared the shit out of me about both overhydrating and dehydrating, how are you supposed to know if you are good and hydrated enough? You're not thirsty. You're not thirsty. You're not thirsty.

That's right. There's this idea that as we're going about our day, once we feel thirsty, it's too late. But Tammy, she just doesn't buy that. And she says there's no magic number of how much water you personally need to drink. It depends on how much you sweat, how hot it is, and how big you are. There are some groups that do need to watch out here.

If you have certain conditions or there's some evidence that as we get older, over 65, our thirst response weakens. But generally speaking, many of us can just trust our bodies to tell us when we need to drink. I spoke to a dozen researchers on this, and nine of them, including Tammy, said that they personally just drank when they were thirsty. As for the others, well, one had kidney stones,

so now drinks more water to avoid getting them again. Science agrees with that. And then there were two left, including Stavros, who liked to drink more often. But given all the research on this, I asked Tammy. So bottom line, of all the things in the world to worry about right now, of which there is a lot, I think you can take your water consumption off that list for the vast majority of people. Is that right?

Yeah, absolutely. Absolutely. Overall, water is not this magic panacea that's going to keep us all healthy. It's not. And we don't all need the same amount. Your body knows exactly how much it needs. Your brain does it for you. That's the thing. Your brain does it for you. And you think you can outsmart your brain. Okay, we're done. We're done. Gallon challenge. Done.

There's no way this made me healthier. No. Agreed. Agreed. Well, cheers to that. Yes. Empty glasses. Empty glasses.

Exactly. Exactly. That's Science Versus. Hello? Hi, Disha Bhagat. Hi, Wendy Zuckerman. How are you feeling? First episode of the season.

Feeling great, yes. How many citations in this week's episode? There are 139 citations. 139. And if people want to see these citations, learn more about hydration, where should they go? They could go to our show notes and there will be links to the transcript. You have survived your first citations. Thanks, Tisha. Bye. Bye. Thanks to all of the researchers who we got in touch with for this episode, including Dr Andrew Brown, Dr Jason Lee Kai, Dr Jodie Stuckey, Dr Vincent Ho, Dr Tristan Struja, Dr Stephen Goodall, Dr Ekua Anobil, Professor Barbara Rolls,

and Dr Krista Kazaza. A special thanks to I'm Wendy Zuckerman. Back to you next time.