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2% Hydration Guide: Part I

2% Hydration Guide: Part I

What you need to know about hydrating and hydration supplements.

You’ll learn: the truth about hydration and performance, how to tell if you’re dehydrated, how dehydration does and does’t impact health, three guidelines for hydrating, and more.

Note: There’s no audio version today. I’m currently recording the audio version of SCARCITY BRAIN, and my voice needs the rest.


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Last week, I was at the community gym. A guy walks in. He’s in his fifties—not the healthiest looking person—and he’s carrying a water bottle.

He got on an elliptical. Then he opened his bottle and dumped in a hydration packet—a popular brand you see all over Instagram and hear advertised on podcasts. He exercised for 10 minutes and left.

The exercise: great!

But I wondered about the hydration packet. It contained a significant amount of salt—and the guy hadn’t sweat.

It made me want to understand hydration better. We’re all told we don’t drink enough water and that we should take electrolyte supplements when we exercise. But what does the research say?

I read studies and called two great experts in this domain, Mike Roussell and Trevor Kashey. Both are PhDs who have conducted research and worked with elite athletes (you can work with them both. Mike is here, Trevor is here. Or follow them on Instagram for their free wisdom. Mike is here. Trevor is here.)

The result is a two-part series on hydration and hydration supplements (a.k.a., electrolyte packets). Today we’ll cover:

  • A brief history of hydration and hydration supplements.
  • What dehydration is and how it impacts us.
  • Whether dehydration affects athletic performance.
  • Three smart guidelines for hydrating around exercise.

On Wednesday, we’ll dive into hydration supplements. We’ll cover:

  • Who may want to use hydration supplements and why.
  • Their potential downsides.
  • The truth about salt and hydration.
  • Whether sugar is good or bad in hydration supplements.
  • What to look for in a hydration supplement.

Let’s roll …

Hydration supplements: a 2297 year history

In short

Rogue experiments on dying prostitutes and mentally ill patients in the 1800s revealed how water and electrolytes impact health.

The details

Erasistratus of Chios was the first physician to start thinking about how water intake and sweat related to health. This was around roughly 275 B.C.

But it wasn’t until the 1600s that legit research began. The Croatian-born medical researcher Santorio Santorio did experiments where he’d feed people specific amounts of food and water then measure how their weight changed as they sweat.

He learned that people constantly gain and lose weight via water throughout the day. More importantly, his work laid the foundation for quantitative experimental medicine—we put numerical measurements onto physiological phenomena for the first time.

A couple hundred years later, we discovered how the balance of salt and water impacts health.

Cholera was ripping through London, thanks to contaminated water. It leads to extreme diarrhea and vomiting, and it was killing anywhere from 20 to 50 percent of the poor who got it.

Cholera patients at the time were being treated with laxatives and other odd remedies.

An old sketch featuring the treatments London’s cholera patients tried.

But a smart doctor named William Brooke O’Shaughnessy conducted experiments where he discovered that cholera patients’ blood seemed to lack water.

He deduced that cholera’s high death rate was related to a lack of water and electrolytes within water. Laxatives were only leading people to lose even more water.

Many cholera patients were so sick they couldn’t even take a drink. So O’Shaughnessy—against recommendations from the medical establishment—started running experiments. He injected patients with a solution of clean water and salt—the first IV.

As the physician and historian Laurence Finberg noted, O'Shaughnessy “chose only the most severely ill patients, many of them prostitutes or derelicts, because death was to be expected and professional criticism, therefore, would be unlikely if he failed.”

This saved many patients. The field of research on hydration—the balance of water and electrolytes and how it relates to health status—was born.

What is dehydration and how does it impact us?

In short

Dehydration generally begins when we lose 2 percent or more of our body weight in water. But there isn’t just one type of dehydration—all forms can cause problems.

The details

Generally, dehydration happens when the water you lose exceeds the water you drink. Issues can start when you lose 2 percent or more of your body weight in liquid. So, for example, if you weighed 150 pounds, that would be 3 pounds, or 48 ounces, of water.

There are a few ways to get dehydrated.

  • Isotonic dehydration occurs when you lose water and sodium together. It happens most commonly through sweating and issues like vomiting and diarrhea.
  • Hypertonic dehydration occurs when the water you lose exceeds the sodium you lose. It happens through fever, heavy breathing, and diabetes.
  • Hyptonic dehydration is when you don’t have enough salt. Diuretics mostly cause it.

Here’s are some of the problems related to dehydration:

  • Fatigue
  • Impaired cognitive function (poorer focus, coordination, executive function).
  • Dizziness
  • Heat exhaustion (if you’re exercising or working outside and not drinking enough).
  • At worst, complications can be heat stroke, kidney issues, seizures, and low blood volume shock. Eventually death.

Obviously, all of those problems ratchet up the more dehydrated a person is.

Is dehydration a problem?

In short

Popular articles say 75% of Americans are dehydrated, but the number is probably much lower. It’s primarily special populations who get dehydrated.

The details

The NIH notes that dehydration isn’t common in adults with no medical problems and easy access to water.

So you probably don’t have to worry about dehydration unless you’re a serious endurance athlete, a manual laborer working in the heat, an older person with mobility problems and a condition like diabetes, or living somewhere without access to clean water.

For example, anywhere from 17 to 28 percent of the elderly are dehydrated. They’re 20 to 30 percent more likely to become dehydrated, for several reasons. For example, they’re not as able to get up and get a glass of water. Their thirst mechanism can become disregulated. They often have diabetes and other conditions that can lead to dehydration.

Construction workers and manual laborers who work outdoors in the summer are another population at risk of dehydration.

As are children in developing countries. This is the biggest problem. Dehydration due to diarrheal disease kills roughly half a million children under five in the developing world each year. (This is why, as Roussell pointed out, clinical-grade rehydration supplements are considered “potentially the most important medical advancement” of the 20th century. They’re estimated to save 1 million lives each year. But we can do better. Donate here.

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Does dehydration impact exercise performance?

In short

You’ll be fine for most workouts so long as you start exercising while hydrated.

The details

You’ve likely read that any water losses while you exercise will tank your performance. And so the implication is that you need to pound water as you run or ruck.

For example, in 2007, The American College of Sports Medicine (ACSM) released a position stating:

“dehydration (of more than 2 percent of your) body weight degrades aerobic exercise performance in temperate-warm-hot environments and that greater levels of dehydration will further degrade aerobic exercise performance.”

But researchers in Canada reviewed all the literature and came to a slightly different conclusion.

Many of those dehydration studies the ACSM cited were conducted in labs and didn’t replicate real-world conditions. The experiments were shown to be unreliable.

So the researchers looked at two different types of data on how hydration impacts performance:

  1. Studies that replicated real-world racing conditions.
  2. Hydration data from actual races.

The surprising result:

  • “None of these studies demonstrate that exercise-induced body weight loss impairs endurance performance.”

The groups that remained better hydrated—losing 0.44 percent of their body weight—actually performed slightly worse than those who became dehydrated and lost more than 2 percent of their body weight.

The scientists also gathered real-world evidence from races like marathons, ultra-marathons, and triathlons.

Generally, the results found that people who lost more water weight performed better.

They found a “significant linear relationship between the degree of body weight loss and race finish time, such that those with the greatest body weight loss had the best racing times.” They gave some examples:

One marathon winner in England lost 6.9 percent of his body weight. The three runners to finish behind him lost, on average, 5.8 percent of their body weight. The winner of the 2009 Dubai marathon, Haile Gebrselassie, completed the race with a body weight loss of 9.8 percent.

  • This doesn’t suggest dehydrating yourself is a performance booster.
  • Rather, it suggests that you can still be successful if you lose more than 2 percent of your body weight in water during an athletic event.

The takeaway for the average person: Unless the conditions are brutally hot, you’ll be fine if you drink water before your average workout lasting 90-ish minutes or less. For longer efforts, bring water. But as Roussell said:

A common pitfall is to wait until you're thirsty to drink and then chug. Don’t do this. Chugging can lead to increased urination. Instead, aim to drink small, frequent amounts throughout your event, even if you don't feel thirsty. The sip strategy not only helps keep you better hydrated throughout the event, it will also help ensure that your body absorbs and effectively uses the hydration you are providing it.

The importance of electrolytes

In short

Electrolytes are obviously important, but you probably don’t have to supplement them for most workouts.

The details

Electrolytes—sodium, potassium, etc—are critical for your body to function. Particularly your muscles and neurons. But we lose these as we sweat.

Hence the shelves of nutrition and outdoor stores are packed with electrolyte supplements—the idea being that adding them back as you train will maintain your performance.

But these likely won’t matter for most workouts. Even up to a couple of hours. Especially if those workouts are indoors and not in brutal heat.

For example, here’s Alex Hutchinson, PhD, arguably the smartest mind on the science of endurance:

To be honest, I’ve never seen convincing evidence that taking in electrolytes during exercise makes much difference. Sure, you need to replenish them eventually—but you’ll get plenty of electrolytes with your next meal. During exercise, the most commonly cited danger of electrolyte depletion is muscle cramping, though the exact cause of cramping remains hotly disputed.

That doesn’t mean they’re useless. At all.

It just means they’re probably useful under certain conditions, and for other surprising workouts (more on that Wednesday). Hutchinson thinks they’re probably helpful if “you’ve been exercising for several hours and (have) lost a lot of sweat.”

What you should do

In short

Drink before you exercise, and to thirst.

The details

Considering some of the surprising data on dehydration and performance, the Canadian scientists wrote:

Although the previous facts indicate that an aggressive defense of body weight during prolonged exercise is clearly not a prerequisite for the achievement of remarkable performance, they should not be taken to suggest that attention should not be paid to hydration during exercise

They offered up three pieces of advices:

Step One: Drink enough before you exercise

When I spoke to Roussell, he referred me to research suggesting that 50 percent of athletes start mildly dehydrated. This is a bad look.

“So step one is don’t go into your workout or event under-hydrated,” said Roussell.

Some evidence suggests starting an event dehydrated can decrease performance. For example, one study found a marker of endurance decreased by 2.9 percent for each percent loss in body weight above a threshold loss of 3.1 percent.

If you have a big event or workout coming up, he recommends that you start to hydrate in the 24 hours leading up to it. I.e., Don’t pound a bunch of water during your warmup.

Let your pee guide you: “Aim for a light straw color in your urine as a simple gauge of hydration status,” said Roussell. If you’re peeing what appears to be the same fluid in highlighter markers, you need more water.

Step Two: Drink according to thirst; no more, no less

That recommendation is quoted directly from those Canadian researchers.

Eight glasses of water throughout the day is a clear recommendation and it’s not necessarily bad advice.

But there’s a lot of variation between people. For example, it seems rather obvious that eight glasses of water might be overdoing it for a sedentary, 110-pound person and underdoing it for a highly active 220-pound person.

If you just drink when you’re thirsty and keep your pee that straw color, you’ll be fine.

The caveat: Thirst sensations can change if you’re deep into a long endurance event. Say, over two hours. So in those cases, just make sure you’re sipping water along the way. Like, if you’ve been running or rucking for two hours straight and sweating, you might want to take a sip of water. Hooray for common sense.

Step Three: Don’t over consume water before or during workouts

This is a delicate balance. Obviously, you need water.

But with that in mind, some people overdo it, pounding water before and during every workout.

Some evidence suggests that this decreases performance. Especially if the workout lasts an hour or less. The scientists wrote:

Trying to fully replace fluid losses during high-intensity exercise may lead to gastrointestinal problems, thereby degrading rather than improving performance.

At worst, drinking far more than usual before or during exercise can cause an exceedingly dangerous condition called Hyponatremia, when the concentration of sodium in your blood drops too low. It’s rare, but can kill.

A quick rapid fire on hydration:

Does coffee dehydrate you?

No. Even if you lose some water due to the diuretic effect of coffee, the water in the coffee exceeds what you lost.

Do drinks that aren’t water count?

Yes! But unless you’re exercising, probably avoid sugars in your liquids.

Are there other ways to hydrate?

Yes! Food counts. For example, lettuce is 96% water. Any food that isn’t purposefully dried contains water and, therefore, keeps you hydrated.

Are there ways beyond electrolyte supplements to get electrolytes?

Yes! Trevor Kashey (much more from him Wednesday) suggested you look on the nutrition label of a bottle of plain water. It says “electrolytes added for flavor.” So you are getting some level of electrolytes from drinking plain water. And, of course, from your food.

Will drinking more water make me healthier?

Not if you’re adequately hydrated. Let your thirst and pee guide you.

Wednesday, we’ll do a deep dive on electrolyte supplements.

  • Who may want use them and why.
  • Their potential downsides.
  • The truth about salt and hydration.
  • Whether sugar is good or bad in hydration supplements.
  • What to look for in a hydration supplement.

Have fun, don’t die, drink water.


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