How to Properly Hydrate & How Much Water to Drink Each Day | Dr. Andrew Huberman
00:00:00.000 | [silence]
00:00:02.420 | How do we actually measure dehydration?
00:00:04.340 | Now, you hear different things.
00:00:05.220 | Like if you pinch the skin on the top of your hand
00:00:07.220 | and it takes more than three seconds
00:00:09.400 | to lay down again flat, then you're dehydrated.
00:00:12.260 | You hear that.
00:00:13.100 | You hear, okay, if you are to press on your fingernail
00:00:16.660 | and see a change in the color of the tissue
00:00:19.980 | just below your fingernail, which indeed does happen,
00:00:23.140 | and it does not go back to its original color
00:00:26.060 | within one to three seconds, then you're dehydrated.
00:00:28.580 | You hear things like this.
00:00:29.420 | If your ankles are swollen when you're wearing socks,
00:00:31.580 | you take off the socks and you can see the imprint
00:00:33.700 | of the socks on your lower limbs,
00:00:36.540 | that means you're dehydrated.
00:00:37.380 | You hear this kind of stuff,
00:00:38.740 | and you should probably be wondering, is any of that true?
00:00:41.820 | To some extent, it is true,
00:00:44.020 | although it can vary quite a bit by how old you are,
00:00:46.660 | whether or not the skin on the top of your hand
00:00:49.180 | tends to be looser or not,
00:00:50.700 | depending on whether or not you're leaner or not.
00:00:53.020 | So in other words, those are not
00:00:55.300 | absolutely objective measures of dehydration.
00:00:57.820 | Now, it is true that if normally you can pinch the skin
00:01:01.180 | on the top of your hand
00:01:02.020 | and it returns to its normal flattened position
00:01:03.980 | within about one to two or three seconds,
00:01:06.660 | and it does not do that within five or more seconds,
00:01:10.620 | there's a decent probability
00:01:12.500 | that you're a little bit dehydrated,
00:01:13.580 | that you need to ingest some fluid,
00:01:15.220 | or that if you press down on your nail
00:01:17.420 | and you see the depression causes a transition
00:01:20.860 | from kind of a pink color to a white color,
00:01:23.860 | and then you release,
00:01:25.020 | and it doesn't go back to its original pinkish color
00:01:28.220 | within a few seconds,
00:01:29.220 | well, then there's a chance that you're dehydrated.
00:01:32.180 | But again, these are not perfect measures of dehydration.
00:01:34.980 | You may be surprised to learn,
00:01:36.180 | and I was surprised to learn,
00:01:37.320 | that most of the basis for these statements,
00:01:40.320 | like even a 2% dehydration state
00:01:44.100 | can lead to significant reductions
00:01:45.780 | in cognitive or physical performance,
00:01:47.700 | are based on not direct measures of hydration,
00:01:51.220 | but rather on measures of reductions in water intake,
00:01:55.600 | which is a different thing, right?
00:01:57.380 | It's saying that ordinarily,
00:01:59.080 | a person of a given body weight
00:02:01.580 | needs X amount of fluid per day,
00:02:04.460 | and when they get even just 2% less
00:02:07.460 | than that amount of fluid,
00:02:08.820 | then their cognitive and/or physical performance is impaired
00:02:12.020 | rather than focusing on dehydration of tissues, right?
00:02:16.300 | Now, that might seem like a subtle distinction,
00:02:18.820 | but it's actually a meaningful distinction
00:02:20.460 | when you think about it.
00:02:21.380 | However, it's a meaningful distinction
00:02:23.640 | that we can leverage toward understanding
00:02:25.380 | how much water or fluid we need to drink each day.
00:02:28.800 | Now, there we can really point to some solid numbers
00:02:31.640 | that, believe it or not,
00:02:32.880 | are fairly independent of body weight.
00:02:34.820 | Now, I say independent of body weight,
00:02:37.500 | I'm referring to the amount of fluid
00:02:39.660 | that most healthy adults need at rest.
00:02:43.300 | What do I mean by at rest?
00:02:44.260 | I mean when not exercising
00:02:46.000 | and when not in extremely hot environment.
00:02:48.700 | So I'm leaving aside you desert ultramarathoners
00:02:52.260 | or people that are doing any kind of movement
00:02:55.700 | or living in environments that are very, very hot.
00:02:59.100 | Here, I'm mainly referring to people
00:03:01.340 | that live most of their daily life in indoor environments.
00:03:05.260 | Could be air-conditioned or not air-conditioned,
00:03:06.820 | heated or not heated.
00:03:08.020 | What we're trying to arrive at here
00:03:09.220 | are some numbers that can work across the board
00:03:11.660 | because, of course, there are an infinite number
00:03:14.620 | of different conditions
00:03:15.500 | that each and all of you are existing in.
00:03:17.580 | So I'm not going to attempt to give you a body weight
00:03:20.500 | by activity, by environment,
00:03:22.420 | by humidity formula calculation.
00:03:24.900 | In fact, no such calculation exists.
00:03:27.300 | However, there are formulas
00:03:29.260 | that can put you into very stable frameworks.
00:03:32.700 | That is levels of water intake for periods of rest
00:03:37.540 | when you're not exercising
00:03:38.860 | and for when you are exercising
00:03:41.660 | that will ensure that you are hydrating
00:03:44.940 | with the one exception being if you are exercising
00:03:48.100 | or if you are living in very, very hot conditions
00:03:51.460 | and you're not heat adapted to those conditions.
00:03:53.740 | So what are those numbers?
00:03:54.860 | In other words, what is the answer to the question
00:03:57.220 | of how much fluid do we need each day?
00:03:59.140 | And here, I'm referring to fluid.
00:04:00.540 | I'm not distinguishing between water,
00:04:02.780 | caffeinated beverages, soda, tea, and so on.
00:04:05.140 | I'll discuss that in a moment.
00:04:06.640 | We can reasonably say that for every hour
00:04:11.980 | that you are awake in the first 10 hours of your day,
00:04:15.960 | this is important, in the first 10 hours of your day,
00:04:18.880 | you should consume on average eight ounces of fluid.
00:04:23.880 | Now, for those of you that are using the metric system,
00:04:27.540 | not ounces, eight ounces of fluid
00:04:30.060 | is approximately 236 milliliters of water.
00:04:34.540 | And for those of you that exist in the metric system
00:04:36.820 | and aren't used to thinking about ounces and vice versa,
00:04:39.940 | just think about a typical can of soda
00:04:42.180 | in the United States is 12 ounces.
00:04:44.980 | In Europe, sometimes the cans of soda
00:04:46.460 | are a little bit smaller.
00:04:47.700 | That's a whole discussion unto itself,
00:04:49.580 | but eight ounces of fluid, that is 236,
00:04:54.580 | let's just say 240 milliliters,
00:04:56.740 | 'cause we don't need to be too precise here,
00:04:58.420 | of fluid on average every hour
00:05:02.420 | for the first 10 hours of your day,
00:05:04.380 | which translates to an average of 80 ounces of fluid
00:05:07.300 | for the first 10 hours of your day.
00:05:09.340 | Or 2,360 milliliters of water,
00:05:13.940 | in other words, approximately two liters of water
00:05:17.900 | plus a little bit more for the first 10 hours of your day.
00:05:22.020 | Now, I want to be very clear that this does not mean
00:05:24.900 | that you need to ingest eight ounces
00:05:27.400 | or 236 milliliters of fluid on the hour,
00:05:30.100 | every hour for the first 10 hours of your day.
00:05:31.900 | I'm certainly not saying that.
00:05:33.300 | And in fact, most people are going to find
00:05:35.700 | that they're going to ingest water in boluses,
00:05:38.600 | that is, they're going to have perhaps 16 ounces of water,
00:05:42.580 | 500 milliliters of water at one portion of the day,
00:05:45.300 | and then maybe a couple hours of later,
00:05:47.140 | they'll drink some more water or some more coffee or soda
00:05:50.140 | or some other beverage in another portion of the day.
00:05:53.780 | I do think, however, it's important for most of us
00:05:56.060 | to take a step back and ask ourselves
00:05:58.460 | whether or not independent of any other activity
00:06:00.620 | or environmental conditions,
00:06:02.020 | whether or not we are in fact ingesting 80 ounces
00:06:06.420 | or basically 2.4 liters of water
00:06:11.160 | for that 10 hours of the day
00:06:13.740 | that spans from the time we wake up until 10 hours later.
00:06:18.320 | Now, why am I setting this 10-hour framework?
00:06:21.160 | The reason I'm setting this 10-hour framework
00:06:23.160 | is that it turns out that your fluid requirements,
00:06:25.720 | even just at rest, are vastly different
00:06:28.600 | in the time from when you wake up
00:06:31.200 | until about 10 hours later
00:06:33.140 | as compared to the later evening and nighttime.
00:06:35.780 | And here I'm referring to people
00:06:36.840 | that are not doing night shifts.
00:06:38.360 | But if you are requesting a number
00:06:40.400 | of how much fluid to drink,
00:06:41.800 | independent of our needs for fluid for exercise,
00:06:45.120 | that's going to be eight ounces of fluid
00:06:47.000 | or 240 milliliters of fluid on average for every hour
00:06:52.000 | from the time we wake up until 10 hours later.
00:06:55.240 | That's the simple formulation
00:06:57.060 | that should basically ensure
00:06:58.920 | that you're getting sufficient baseline hydration
00:07:01.960 | for the cells and tissues of your body.
00:07:03.880 | Now, if you are engaging in exercise,
00:07:06.740 | whether or not it's endurance exercise
00:07:08.180 | or whether or not it's resistance training exercise,
00:07:10.540 | you are going to need additional fluids
00:07:12.420 | in order to maximize the effects of that exercise
00:07:16.180 | and to avoid dehydration.
00:07:18.260 | And there too, we have some excellent numbers
00:07:20.520 | that we can look to,
00:07:21.360 | excellent because they arrive from research.
00:07:23.980 | And this is largely peeled from the episode
00:07:27.260 | that I did with Dr. Andy Galpin,
00:07:28.540 | professor of kinesiology at Cal State Fullerton.
00:07:30.500 | We did a six-episode series all about exercise,
00:07:32.780 | everything from strength training, hypertrophy, endurance,
00:07:35.400 | nutrition, supplementation, recovery,
00:07:36.800 | everything related to exercise.
00:07:38.400 | You can find all of that at hubermanlab.com.
00:07:40.160 | And one of the components of those episodes
00:07:43.000 | that was discussed but that some of you may have not heard
00:07:46.260 | is that there is a simple formula
00:07:48.680 | for how much fluid to ingest on average.
00:07:50.880 | Keep in mind, this is on average when you're exercising.
00:07:54.920 | And I refer to this as the so-called Galpin equation.
00:07:59.140 | The Galpin equation states
00:08:01.000 | that you should take your body weight in pounds,
00:08:04.100 | divide that by 30,
00:08:06.200 | and that will give you the number of ounces of fluid
00:08:08.800 | to ingest every 15 to 20 minutes on average
00:08:12.700 | while exercising, okay?
00:08:14.600 | Your body weight in pounds divided by 30
00:08:18.540 | equals the number of ounces of fluid to consume
00:08:21.320 | on average every 15 to 20 minutes.
00:08:23.260 | When I say on average, what I mean is
00:08:25.140 | it is not the case that you need to stop
00:08:27.580 | every 15 or 20 minutes
00:08:28.820 | and consume that volume of fluid.
00:08:31.560 | You could sip it from moment to moment.
00:08:33.780 | You could wait half an hour or an hour
00:08:36.340 | and then consume a larger bolus of fluid, a larger amount.
00:08:39.820 | Although it is recommended for performance sake
00:08:43.180 | that you sip or consume beverages
00:08:47.060 | fairly consistently throughout your training.
00:08:50.520 | One's ability to do that
00:08:51.620 | is going to depend on a number of things
00:08:53.020 | like gastric emptying time,
00:08:55.120 | whether or not the particular exercise you're doing,
00:08:57.080 | whether or not it's running or jumping
00:08:58.980 | is compatible with ingesting fluid on a regular basis
00:09:02.060 | or whether or not you need to do it at different intervals
00:09:04.220 | than every 15, 20 minutes.
00:09:05.500 | Maybe it's every five minutes.
00:09:06.500 | Maybe it's every half hour.
00:09:08.020 | You have to adjust for you.
00:09:09.120 | But if you were to take the hour of exercise
00:09:11.700 | or the half hour of exercise
00:09:13.740 | or the three hours of exercise
00:09:15.700 | and ask how much fluid to ingest,
00:09:18.140 | it's going to be that Galpin equation
00:09:19.660 | of body weight in pounds divided by 30
00:09:21.020 | equals the number of ounces for every 15 or 20 minutes.
00:09:23.660 | And of course I can already hear screaming from the back,
00:09:26.180 | what about for those of us who follow the metric system?
00:09:29.260 | And there there's a simple translation
00:09:31.280 | of the Galpin equation,
00:09:32.440 | which is that you need approximately two milliliters of water
00:09:37.040 | per kilogram of body weight every 15 to 20 minutes.
00:09:40.260 | Again, the Galpin equation converted into the metric system
00:09:43.720 | is going to be two milliliters of water
00:09:45.680 | per kilogram of body weight
00:09:46.960 | every 15 to 20 minutes on average.
00:09:49.720 | I'm sure a number of you are asking
00:09:51.000 | whether or not hydration prior to exercise
00:09:53.600 | is also important.
00:09:54.440 | It absolutely is.
00:09:55.260 | And if you follow the numbers that I talked about before,
00:09:58.320 | approximately eight ounces or 240 milliliters
00:10:02.200 | of fluid intake per hour in the first 10 hours of waking,
00:10:07.120 | that should establish a good baseline
00:10:09.320 | of hydration heading into exercise,
00:10:11.500 | which then prompts the next question I often get,
00:10:13.880 | which is, is the amount of water that needs to be consumed
00:10:17.280 | according to the Galpin equation during exercise
00:10:19.660 | on top of or separate from,
00:10:22.600 | that is, does it replace the amount of fluid
00:10:24.240 | that one needs at a basic level,
00:10:27.640 | that eight ounces or 240 milliliters?
00:10:29.560 | And there, the answer sort of goes both ways.
00:10:32.340 | I think if you're going to exercise,
00:10:34.360 | then obviously follow the Galpin equation in some way.
00:10:38.640 | Again, you don't need to be ultra specific about this.
00:10:41.080 | These are ballpark figures that will ensure hydration.
00:10:43.900 | So we've set them a little bit higher perhaps than needed
00:10:46.360 | to ensure more hydration rather than less.
00:10:49.880 | But basically the short answer is
00:10:52.160 | if you're exercising for about an hour,
00:10:53.800 | most people are exercising for an hour or two,
00:10:55.760 | probably not more than that.
00:10:56.680 | Most of my workouts are,
00:10:58.280 | certainly the resistance training workouts
00:10:59.820 | last about an hour.
00:11:01.200 | Well, then you can replace the eight ounces
00:11:03.600 | or the 240 milliliters of water
00:11:05.540 | that's required at baseline with what you consume
00:11:07.800 | according to the Galpin equation
00:11:09.400 | during that bout of exercise.
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