How to Properly Hydrate & How Much Water to Drink Each Day | Dr. Andrew Huberman

Summary

There are common rules of thumb for assessing hydration status, like pinching skin or checking nail beds, but these are imperfect measures. Research linking cognitive deficits to low fluid intake may conflate dehydration with insufficient drinking. A simple formula for baseline hydration is 8 oz (240 ml) of fluid per waking hour for the first 10 hours. During exercise, consume fluid equal to your weight in pounds divided by 30 oz per 15-20 minutes. This replaces baseline intake. Metric system: 2 ml per kg body weight per 15-20 minutes. Adequate hydration optimizes physical and cognitive performance.

Takeaways

• 😀 For healthy adults at rest, aim to drink 8 oz (240 mL) of fluid per hour for the first 10 waking hours. This equals about 80 oz or 2.4 liters per day.
• 😊 There are no definitive objective measures of dehydration based on skin turgor, nail beds, etc. These are imperfect and vary greatly between people.
• 🤔 Most data linking mild dehydration to performance impairments is based on reduced fluid intake rather than direct measures of tissue dehydration.
• 😮 Fluid needs are much higher in the first 10 hours after waking compared to evening/night. Adjust intake accordingly.
• 🙂 For exercise, drink your body weight (lbs)/30 oz fluid every 15-20 min on average, or 2 mL/kg body weight for metric.
• 😃 Hydrating well before and during exercise, per the above guidelines, optimizes performance and avoids dehydration.
• 👍 Ingesting fluids consistently in smaller amounts is optimal, but larger boluses spaced further apart can also work.
• 🤓 If exercising for about an hour, the fluid intake can generally replace baseline hourly fluid needs of 8 oz/240 mL.
• 😕 Extreme environments and activities like desert marathons require additional fluid above these baseline recommendations.
• 😉 Simple frameworks for rest, exercise and metric system make hydration recommendations easy to follow.

Q & A

How can you determine if you are dehydrated based on the skin on the top of your hand?

If you pinch the skin on top of your hand and it takes more than 3 seconds to lay back down flat, there is a decent probability you are a little dehydrated and need to ingest some fluid.

What is the difference between measuring dehydration based on water intake versus tissue dehydration?

Measuring based on water intake looks at reductions in the amount of water consumed compared to normal. Measuring tissue dehydration looks directly at the dehydration of body tissues.

What is the baseline fluid intake recommendation for adults at rest?

8 ounces (236 ml) of fluid per hour for the first 10 hours after waking up, which equals about 80 ounces (2.36 liters) per day.

What is the Galpin Equation for fluid intake when exercising?

Take your body weight in pounds and divide by 30 to get the ounces of fluid to consume every 15-20 minutes on average.

How do you convert the Galpin Equation to the metric system?

Consume 2 ml of fluid per kg of body weight every 15-20 minutes on average.

Should you hydrate before exercising?

Yes, following the baseline recommendation of 8 oz/236 ml per hour in the first 10 hours of the day will help establish good hydration before a workout.

Does the Galpin Equation fluid replace or add to the baseline fluid needed?

For about 1-2 hours of exercise it generally replaces the baseline fluid intake. For longer workouts it adds on top of baseline needs.

Do the skin pinch and fingernail press tests definitively show dehydration?

No, they are not perfect or definitive measures of dehydration. But they can indicate the likelihood of some level of dehydration.

Why is the first 10 hours important in the baseline recommendation?

Your fluid needs are much higher in the first 10 hours after waking compared to the evening and nighttime hours.

How should you time your fluid intake when exercising?

Ideally sip consistently throughout exercise according to what works for your sport and gastric emptying rate. But total intake should aim to match the Galpin Equation.

Outlines

00:00

😅 How dehydration is measured

This paragraph discusses different methods people use to measure dehydration, like pinching the skin on your hand to see how long it takes to flatten, pressing on fingernails to check capillary refill time, checking for swollen ankles, etc. It explains that while these methods provide some indication of dehydration, they are not completely reliable or objective measures.

05:00

💧 Recommended daily fluid intake

This paragraph provides specific recommendations for daily fluid intake needs. It suggests ingesting 8 oz (or 240 ml) of fluid per hour for the first 10 hours you're awake, working out to 80 oz (or 2.36 liters) over those 10 hours. It clarifies this is not meant to be consumed strictly on the hour, but provides a framework for adequate hydration.

10:05

🚰 Hydration needs during exercise

This paragraph discusses additional fluid needs while exercising, providing the 'Galpin Equation' formula to calculate recommended fluid intake. It suggests dividing your body weight in pounds by 30 to get the ounces to consume every 15-20 minutes on average. It also provides the metric conversion of 2 ml per kg of body weight.

Keywords

💡dehydration

Dehydration refers to the loss of water and fluids from the body. It is a key concept in the video, as the narrator tries to provide methods for measuring dehydration levels and recommendations for maintaining proper hydration.

💡fluid intake

Fluid intake refers to the amount of liquids consumed, including water, juices, tea, coffee, soda, etc. The video focuses heavily on recommendations for baseline daily fluid intake to avoid dehydration.

💡Galpin equation

The Galpin equation was developed by physiologist Dr. Andy Galpin to calculate optimal fluid intake during exercise. It states that you need to consume your body weight (in lbs) divided by 30, in ounces of fluid, every 15-20 minutes during exercise.

💡hydration

Proper hydration refers to maintaining adequate water and fluid levels in the body's cells and tissues. The video provides specific guidelines for baseline hydration and additional hydration needs during exercise.

💡metrics

Metrics and measurements refer to the indicators used to quantitatively assess the hydration state and fluid levels in the body. The narrator examines common metrics but notes they have limitations in terms of objectivity and consistency across individuals.

💡baseline

The baseline refers to standard daily fluid intake needs for most healthy adults at rest (not exercising or in hot climates). The video recommends 8 oz of fluid intake per hour for the first 10 hours awake, equating to 80 oz or 2.36 liters total.

💡boluses

Fluid boluses are larger volumes of liquid ingested at once rather than small constant sips. The scripts notes people tend to consume fluids in boluses over the day rather than at strict hourly intervals.

💡cognitive performance

Cognitive performance refers to brain functions like thinking, focus, and decision making. The video claims that research shows even mild dehydration can substantially reduce mental/cognitive performance.

💡endurance exercise

Endurance exercise like running involves sustained activity over longer periods. This type of exercise leads to major fluid losses, so the video provides specific guidelines for fluid intake rates during endurance training.

💡resistance training

Resistance training includes weight lifting, strength training, etc. This also increases hydration needs, albeit less than endurance exercise. But the Galpin equation provides fluid recommendations for resistance training too.

Highlights

How much fluid do we need each day? About 80 ounces or 2.4 liters for the first 10 waking hours.

Ingest 8 ounces or 240 mL of fluid per hour on average for the first 10 waking hours.

Fluid needs are much higher in the first 10 hours after waking compared to evening/night.

The Galpin Equation calculates fluid needs during exercise: Body weight (lbs) / 30 = ounces per 15-20 mins.

Metric version: 2 mL per kg body weight per 15-20 mins during exercise.

Hydrating prior to exercise by following the baseline recommendation is important.

Fluid consumed during exercise generally replaces baseline hydration needs.

Skin pinch time, nail bed color, and imprinted socks are not perfect hydration measures.

Most hydration guidelines for cognition/performance are based on reduced water intake, not tissue dehydration.

Distinction between water intake and tissue dehydration is meaningful for understanding needs.

Formulas provide framework for sufficient hydration excluding extreme heat/exercise.

Ingesting fluid consistently during exercise optimizes performance.

Adjust fluid intake timing/amount for individual exercise compatibility.

Numbers provided intentionally exceed needs to ensure adequate hydration.

See hubermanlab.com exercise series for more on hydration and performance.

Transcripts

How do we actually measure dehydration?

Now you hear different things

like if you pinch the skin on the top of your hand

and it takes more than three seconds to

lay down again flat, then you're dehydrated.

You hear that.

You hear, okay, if you are to press on your fingernail

and see a change in the color of the tissue

just below your fingernail, which indeed does happen,

and it does not go back to its original color

within one to three seconds, then you're dehydrated.

You hear things like this.

If your ankles are swollen when you're wearing socks,

you take off the socks

and you can see the imprint of the socks

on your lower limbs, that means you're dehydrated.

You hear this kind of stuff,

and you should probably be wondering, is any of that true?

To some extent, it is true,

although it can vary quite a bit by how old you are,

whether or not the skin on the top of your hand

tends to be looser or not,

depending on whether or not you're leaner or not.

So, in other words,

those are not absolutely objective measures of dehydration.

Now, it is true that if normally

you can pinch the skin on the top of your hand

and it returns to its normal flattened position

within about one to two or three seconds,

and it does not do that within five or more seconds,

there's a decent probability

that you're a little bit dehydrated,

that you need to ingest some fluid,

or that if you press down on your nail

and you see the depression causes a transition from

kind of a pink color to a white color,

and then you release

and it doesn't go back to its original pinkish color

within a few seconds,

well, then there's a chance that you're dehydrated.

But again, these are not perfect measures of dehydration.

You may be surprised to learn, and I was surprised to learn,

that most of the basis for these statements,

like even a 2%

dehydration state can lead to significant reductions

in cognitive physical or performance

are based on not direct measures of hydration,

but rather on measures of reductions in water intake,

which is a different thing, right?

It's saying that ordinarily

a person of a given body weight needs

X amount of fluid per day,

and when they get even just 2% less

than that amount of fluid,

then their cognitive and or physical performance is impaired

rather than focusing on dehydration of tissues.

Now that might seem like a subtle distinction,

but it's actually a meaningful distinction

when you think about it.

However, it's a meaningful distinction

that we can leverage toward understanding

how much water or fluid we need to drink each day.

Now, there we can really point to some solid numbers

that, believe it or not,

are fairly independent of body weight.

Now, I say independent of body weight,

I'm referring to the amount of fluid

that most healthy adults need at rest.

What do I mean by at rest?

I mean when not exercising

and when not in extremely hot environments.

So I'm leaving aside you desert ultra marathoners

or people that are doing any kind of movement

or living in environments that are very, very hot.

Here, I'm mainly referring to people that

live most of their daily life in indoor environments,

could be air conditioned or not air conditioned,

heated or not heated.

What we're trying to arrive at here are some numbers

that can work across the board

because of course there are an infinite number

of different conditions

that each and all of you are existing in.

So I'm not going to attempt to give you a body weight

by activity, by environment, by humidity

formula calculation.

In fact, no such calculation exists.

However, there are formulas

that can put you into very stable frameworks.

That is levels of water intake

for periods of rest when you're not exercising

and for when you are exercising

that will ensure that you are hydrating,

with the one exception being if you are exercising

or if you are living in very, very hot conditions

and you're not heat adapted to those conditions.

So what are those numbers?

In other words, what is the answer to the question of

how much fluid do we need each day?

And here I'm referring to fluid.

I'm not distinguishing between water, caffeinated beverages,

soda, tea, and so on.

I'll discuss that in a moment.

We can reasonably say

that for every hour that you are awake,

in the first 10 hours of your day, this is important.

In the first 10 hours of your day,

you should consume on average eight ounces of fluid.

Now, for those of you that are using the metric system,

not ounces,

eight ounces of fluid is approximately

236 milliliters of water.

And for those of you that exist in the metric system

and aren't used to thinking about ounces and vice versa,

just think about a typical can of soda in the United States,

it's 12 ounces.

In Europe, sometimes the cans of soda

are a little bit smaller.

That's a whole discussion unto itself.

But eight ounces of fluid, that is

236.

So let's just say 240 milliliters,

'cause we don't need to be too precise here,

of fluid

on average

every hour

for the first 10 hours of your day,

which translates to an average of 80 ounces of fluid

for the first 10 hours of your day,

or

2,360

milliliters of water.

In other words, approximately two liters of water

plus a little bit more for the first 10 hours of your day.

Now, I want to be very clear

that this does not mean that you need to

ingest eight ounces or 236 milliliters of fluid

on the hour every hour for the first 10 hours of your day.

I'm certainly not saying that.

And in fact, most people are going to find

that they're going to ingest water in boluses.

That is, they're going to have perhaps 16 ounces of water,

500 milliliters of water at one portion of the day,

and then maybe a couple hours of later

they'll drink some more water

or some more coffee or soda or some other beverage

in another portion of the day.

I do think, however, it's important for most of us

to take a step back and ask ourselves

whether or not independent of any other activity

or environmental conditions,

whether or not we are in fact ingesting 80 ounces,

or

basically 2.4 liters of water

for that 10 hours of the day

that spans from the time we wake up until 10 hours later.

Now, why am I setting this 10 hour framework?

The reason I'm setting this 10 hour framework

is that it turns out that your fluid requirements,

even just at rest,

are vastly different in the time from when you wake up

until about 10 hours later

as compared to the later evening and nighttime.

And here I'm referring to people

that are not doing night shifts,

but if you are requesting a number

of how much fluid to drink independent of our needs

for fluid for exercise,

that's going to be eight ounces of fluid

or 240 milliliters of fluid

on average

for every hour from the time when we wake up

until 10 hours later.

That's the simple formulation that should basically ensure

that you're getting sufficient baseline hydration

for the cells and tissues of your body.

Now, if you are engaging in exercise,

whether or not it's endurance exercise

or whether or not it's resistance training exercise,

you are going to need additional fluids

in order to maximize the effects of that exercise

and to avoid dehydration.

And there too,

we have some excellent numbers that we can look to,

excellent because they arrive from research.

And this is largely peeled from the episode

that I did with Dr. Andy Galpin,

Professor of Kinesiology at Cal State Fullerton.

We did a six episode series all about exercise,

everything from strength training, hypertrophy, endurance,

nutrition, supplementation, recovery,

everything related to exercise.

You can find all of that at hubermanlab.com.

And one of the components

of those episodes that was discussed,

but that some of you may have not heard,

is that there is a simple formula

for how much fluid to ingest, on average,

keep in mind this is on average when you are exercising,

and I refer to this as the so-called Galpin Equation.

The Galpin Equation states that

you should take your body weight in pounds,

divide that by 30,

and that will give you the number of ounces of fluid

to ingest every 15 to 20 minutes on average

while exercising.

Your body weight in pounds divided by 30

equals the number of ounces of fluid to consume on average

every 15 to 20 minutes.

When I say on average, what I mean is it is not the case

that you need to stop every 15 or 20 minutes

and consume that volume of fluid.

You could sip it from moment to moment.

You could wait half an hour or an hour

and then consume a larger bolus of fluid, a larger amount,

although it is recommended for performance sake

that you

sip or consume beverages

fairly consistently throughout your training.

One's ability to do that

is going to depend on a number of things

like gastric emptying time,

whether or not the particular exercise you're doing,

whether or not it's running or jumping,

is compatible with ingesting fluid on a regular basis,

or whether or not you need to do it at different intervals

than every 15, 20 minutes.

Maybe it's every five minutes, maybe it's every half hour,

you have to adjust for you.

But if you were to take the hour of exercise

or the half hour of exercise

or the three hours of exercise

and ask how much fluid to ingest,

it's going to be that Galpin Equation

of body weight and pounds divided by 30

equals the number of ounces for every 15 or 20 minutes.

And of course, I can already hear screaming from the back.

What about for those of us who follow the metric system?

And there there's a simple translation

of the Galpin Equation,

which is that you need approximately

two milliliters of water per kilogram of body weight

every 15 to 20 minutes.

Again, the Galpin Equation converted into the metric system

is going to be two milliliters of water

per kilogram of body weight

every 15 to 20 minutes on average.

I'm sure a number of you are asking whether or not

hydration prior to exercise is also important.

It absolutely is.

And if you follow the numbers that I talked about before,

approximately eight ounces

or 240 milliliters of fluid intake per hour

in the first 10 hours of waking,

that should establish a good baseline of hydration

heading into exercise,

which then prompts the next question I often get which is,

is the amount of water that needs to be consumed

according to the Galpin Equation during exercise on top of

or separate from,

that is does it replace the amount of fluid that one needs

at a basic level, that eight ounces or 240 milliliters?

And there the answer sort of goes both ways.

I think if you're going to exercise,

then obviously follow the Galpin Equation in some way.

Again, you don't need to be ultra specific about this.

These are ballpark figures that will ensure hydration.

So we've set them a little bit higher perhaps than needed

to ensure more hydration rather rather than less.

But basically the short answer is,

if you're exercising for about an hour,

most people are exercising for an hour or two,

probably not more than that.

Most of my workouts are,

certainly the resistant training workouts

last about an hour.

Well, then you can replace the eight ounces

or the 240 milliliters of water that's required at baseline

with what you consume according to the Galpin Equation

during that about of exercise.

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