'You NEED 8 glasses of water a day!': MYTH or FACT?!

We've all heard the recommendation to drink 8 glasses of water a day. But is it based on sound science?

Do we really need or 8 glasses of water a day? We’ve all heard this advice but I’ve never seen any evidence so I decided to dig around.

I found a lot of interesting research on hydration but nothing pointing to 8 glasses specifically.

There’s mixed evidence on heart disease and cancer and nothing about the 8 glass range.

The evidence on skin health suggests people who drinks very little and are dehydrated may improve some skin properties by upping water intake.

Several experts recommend just trusting your thirst, drinking when thirsty and not obsessing over drinking more water.

Special situations where it may make sense to try to drink more:
If you exercise you lose more water so you need to increase intake; if you live somewhere warm; If out working or exercising in the sun you’ll lose water very fast so it’s a good idea to hydrate in advance even before thirst hits; pregnant or breast-feeding; in children and older people sometimes thirst alone isnt effective. E.g. the thirst reflex goes down with age; If you have kidney stones or a family history, you definitely want to drink more water; extra hydration can help prevent UTIs and it can help with chronic constipation as well

Can drinking more water help us lose weight? Energy expenditure goes up after we drink water. Drinking water before meals can help eat less and lose weight.

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Animations: Even Topland @toplandmedia

References:

Disclaimer: The contents are for informational purposes only and not intended as medical advice, diagnosis, or treatment, nor to replace medical care. The information presented is accurate and conforms to the available scientific evidence to the best of our knowledge. Always seek the advice of your physician or other qualified health provider with questions regarding any medical condition. Never disregard professional medical advice or delay seeking it.

#NutritionMadeSimple #GilCarvalho

0:00 8 glasses a day
0:27 Water & Heart Disease
1:02 Water & Cancer
2:03 Water & Skin
5:20 Special situations
8:36 Water & Weight Loss
12:08 Water & Migraine
12:47 Replacement
13:11 Risks of drinking more water
14:02 Water in food
14:25 Coffe, alcohol & (de)hydration
15:58 Does thirst mean dehydration?
16:44 Urine color & dehydration
17:58 A nephrologist speaks
19:43 Origins of "8 glasses"
20:36 Takeaways

[dalysea]

Thanks for including the fact that coffee still counts! When people would suggest 8 cups of water a day to me, and I would tell them I do get that amount including the tea I drink, they were adamant that tea doesn't count. The idea that throwing a little tea bag in a cup of water was enough to completely negate the benefit of the water always seemed absurd to me. A little googling told me caffeine isn't even that strong of a diuretic, and the amount in tea definitely isn't. I like a little flavor in my water, stop flavor-shaming me! 🤣

[lilytea]

0:16: 🧪 There is mixed evidence on the recommended daily intake of water and its impact on health.
3:18: 🥤 Increasing water intake can improve skin hydration, but the effect depends on the individual's initial water consumption.
6:42: 🚰 Drinking a lot of water may slow down cyst growth in polycystic kidney disease, but there is no evidence to support the recommendation of drinking eight glasses a day for everyone.
10:02: 🥛 Drinking water before meals can lead to a modest weight loss over a few months.
13:18: 🥤 Hyponatremia, a low level of sodium in the blood, is rare and usually occurs in specific circumstances such as underlying health issues or excessive water intake by endurance athletes.
16:43: 🚰 The belief that clear or pale yellow urine indicates hydration is false; urine color varies and does not necessarily reflect hydration levels.
20:11: 🥤 Most people don't need to obsess over drinking a specific amount of water, but it's okay if they want to drink more.
Recap by Tammy AI

[drott]

Yet another amazing and very informative video. The attention to nuance, subtlety and detail in _competently_ reviewing the evidence is what really sets this channel apart. Also, the absolute lack of sensationalism, grifting or clickbait is truly a godsend and so rare in med help youtube channels. You are literally acting as a real, competent and well-intentioned doctor with no axe to grind who is truly helping millions of people with your level-headed, accurate and honest presentation. I know it must have occurred to you that you could make more money by selling out and using the nefarious techniques other youtube "doctors" use, but you remain steadfast and true. It is noticed and very much appreciated. And over time, I am confident you will build your brand and business success as more and more people realize what you offer.

[samuraibat]

When I voted for this in your poll I wasn't expecting a 21 minute video that was so in depth. I should have known better! Good video, doc.

[Rikavich]

Metaphorically spat out my water when you mentioned that ADPKD runs in your family. It's so rare to see it mentioned in the wild, let alone from your favorite nutrition Youtuber! It runs in my family as well, and I had the misfortune of suffering from an aggressive presentation of the disease that led to renal failure two years ago at the age of 40 despite a healthy lifestyle. Thankfully that same year I received a transplant, followed by a bilateral nephrectomy a year later as the size of the kidneys was causing significant discomfort. Doing much better now and continuing to drink a lot of water as per my nephrologists' recommendations. Hope you never get to that point Gil (assuming you carry the mutation). Some of my older family members, including the person I inherited PKD from, have much milder presentations and have never required major medical intervention.

[contextwithjohnmalone]

I’m part of the 27% who requested this video from your poll I’m your community tab. I’m a literal sponge for knowledge (pardon the pun).
I love stats and figures and studies. I feel like they help us all make informed decisions. Thanks for this video Gil.

[Anarcath]

I've been preoccupied with hydration for so many years forcing myself to drink the 8 glasses and often failing and feeling bad about it. A load off my mind. This is very informative.

[scienceislove]

I sometimes don't skip your ad.. hope that helps.. that's the best i can do right now..
I respect your selfless work..
And lord how criminally underated you are.. this just is not fair.. people spreading misinformation are getting a lot more views.. so many stupid chiropractors out there on the internet.. so overrated..

[justanotherfrog]

I just discovered your channel and I love how balanced and science based it is. It would be really great if you could do a video on ghee and coconut oil— lately I hear a lot of people insisting these are better than vegetable or seed oils and I’d love to see the science on this. Thanks!

[MKstudiovideo]

Wow, thanks Gil for this epic summary! Exactly what I've been looking for😍 I would just add that for people with a family history of gout and elevated uric acid levels, it's also recommended to drink more fluids. Also for the complete picture, there're some studies showing a benefit of drinking more for a better cognitive performance, i.e. being dehydrated decreases our cognitive performance.

[jimatsydney]

In 2014 a 100 km ultra trail run I was in had a 30% drop out rate. The next year, after investigating the causes, the organisors advised the participants to only drink when thirsty and to avoid non-steroidal anti-inflamitories. That year they had a 5% drop out rate.

[jeffreymagedanz]

I have a tendency to drink excessive amounts of water and go to the bathroom excessively. Whenever I say anything about trying to cut down, people are always shocked and tell me not to because water is super healthy and more water is always better.

[krc]

My mother and father in law, both over 85 have had trips to ER for UTIs and been told they were not drinking enough water. We've tried since then to get them to drink at least 6 a day. As u said they are never thirsty and so forget to drink water.

[BonytoBeastly]

Awesome video! My understanding of the research is the same as yours, but there's some evidence showing that ensuring proper hydration can improve exercise performance. So if someone is working out, replenishing the water they use is important, but they may also want to preemptively drink a bit more water to get a better workout in.

For example, here's the title of one of the more recent studies linking hydration and exercise performance: Hypohydration but not menstrual phase influences pain perception in healthy women

[alfonso]

The 8 glasses of water recommendation comes from the Harris-Benedict formula. You need about 1 cc of water for every calorie you metabolize. If you consume the typical 2000 calorie diet, you need about 2000 cc of water... Which is about 8 glasses. You will need more if you consume more calories, eat more salt, sweat more, or suffer a specific illness, as mentioned in the video...

[RoxanneRichardson]

I'm an all-day sipper, and always have been (my mom was the same way). I probably average about 8oz (close to 250 ml) of fluid intake every hour from 6 am to 5 or 6 pm, and then I'm done for the day. I rarely just down an entire glass of water in one go. I do pee a lot, but I work from home, so no biggie.

[jorgefernandes]

Came across your channel and it has quickly become a favorite, I thought I heard a little Portuguese in that accent. Great to see a fellow Lusitanian producing such great

[Moriah]

Can you please do a video on coffee? I hear so many mixed messages on whether coffee is healthy or harmful. And the pesticides in coffee, are those actually something to be worried about?

[samuelnazaroff]

I've had a long history of kidney stone issues and even acute kidney failure in 2019. I was advised to drink around 4 liters of water a day and I get anywhere from 16-20 cups since I fill my water up at the beginning of the day and make it a priority to make sure I get the water intake. Have not had a kidney problem or stones (or at least a noticeable one) in the past 3 years. My question is why it is that how much you urinate is more the important metric than how much water we actually drink in the case of stones?

[felicialin]

I love water! For so long, it’s been the only thing that really quenches my thirst and cools me off after a nice long walk! Thanks for the science!