Does drinking water help you lose weight?

From the desk of
Robb Wolf
ScienceDoes drinking water help you lose weight?

About 45 million Americans start a weight loss diet every year. The vast majority of these diets fail.

Would drinking more water turn these failures around? Is H2O the secret to losing weight?

I seriously doubt it. The mechanisms by which drinking water promotes weight loss—and I’ll cover them shortly—pale in comparison to the obesogenic forces of modern society.

These are the forces of sleep deprivation, hyperpalatable foods, constant stress, and insufficient social connection. This modern environment is NOT the environment we evolved to thrive in.

We evolved to eat whole, unprocessed foods that changed with the seasons. We evolved to move frequently, building shelters and hunting animals. And we had plenty of downtime for sleep and socialization.

All these factors sum to a lean, powerful, happy human. Subtract them and we become fat, sick, and sad.

Isn’t Water Important?

You’ll notice that drinking water isn’t on my list of thriving factors. That’s not a mistake.

I’m not saying water isn’t important. Water keeps blood flowing through our veins, our brain floating in our skull, and our waste disposal system doing its job smoothly.

If you stopped drinking water, you would croak in a matter of days. It wouldn’t be pretty. But I’m not worried about that happening. Why? Because you have a snazzy impulse called thirst.

When your blood volume gets low (a sign of insufficient water), specialized receptors in the brain pick up on that. Then they tell a brain region called the hypothalamus to make you thirsty. There are other thirst triggers too, like rising antidiuretic hormone (ADH). But it all runs through the hypothalamus.

Armed with the thirst mechanism, healthy people rarely become dehydrated. Contrary to popular belief, most folks aren’t walking around needing more water.

But let’s say you drink more water anyway. Can that help with weight loss?

How Drinking Water May Help With Weight Loss

Water is essential for life, so getting enough of it is essential for any health regimen. (I’ll cover how to stay hydrated later). But let’s talk about the notion that drinking water may assist with weight loss. There are three potential connections:

#1: Less overeating

Satiety is a complex system. You’re satisfied after a feast, but you might also be satisfied after an overnight fast. Hunger hormones shift throughout the day, and they’re not always tied to when you last ate.

Drinking water shouldn’t meaningfully affect hunger hormones, but it might temporarily trick your stomach into thinking it’s full. There’s only so much room in that organ.

In one small study, fourteen men consumed less food after drinking two glasses of water before a meal compared to controls. The water preload, the authors report, increased fullness and decreased hunger.

But I’m not convinced the effect is meaningful. It was just for one meal. Would the water group catch up on calories later? Hard to say, but I believe they would. You can fool your body for a few minutes, but you can’t fool it for long. It knows when calories aren’t coming in.

Another study found that 50 overweight girls lost weight after drinking 2 cups of water before every meal for eight weeks. But there was no control group, so we can’t conclude much from it.

One more note. I’m not crazy about the pre-meal H2O strategy because water dilutes your stomach acid. That’s not good for digestion.

#2: Increased thermogenesis

Thermogenesis is the creation of heat in your body. This creation of heat requires energy in the form of calories.

If you sit in a tub of ice water, your body needs to create heat to keep you warm. You’ll shiver and thermogenesis will kick in, creating heat by burning calories.

A much smaller effect occurs when you drink water. One paper, for instance, found that drinking 500 mL of room temperature water increased energy expenditure (due to thermogenesis) by 30% for about an hour. Much of this required energy went towards warming up the water in the participants’ bodies.

This sounds significant, but consider that similar (or greater) thermic effects occur when you:

  • Eat food
  • Shiver
  • Exercise

While it does look like a cool glass of liquid temporarily increases energy burn, I must remind you: exercise, quality sleep, a healthy diet, and proper hydration come first. So if you’re thirsty, it can’t hurt—but overhydration is also a real thing, folks. More on that later.

#3: Prevents dehydration

If you ignore the dictates of thirst—or sweat excessively without replacing fluids—you will likely become dehydrated. The symptoms of dehydration include:

  • Headaches
  • Fatigue
  • Muscle cramps
  • Nausea
  • Malaise

Theoretically, all these symptoms could hinder weight loss efforts by cutting into your exercise motivation. But even still, one randomized controlled trial found that dehydration did NOT impair exercise performance in trained cyclists pedaling in the heat.

Being dehydrated also hinders lipolysis (the breaking apart of body fat). But if you’re drinking to thirst, this shouldn’t be an issue.

The Problem With Drinking Too Much Water

We’re told to drink eight glasses of water per day, even if we’re not thirsty. This recommendation has ZERO science behind it, but it’s widely accepted as sage advice.

It’s not sage advice. Drinking too much plain water dilutes blood sodium levels, and low sodium levels can be quite dangerous.

These dangers are most obvious in endurance sports. Encouraged to hydrate aggressively while training and racing, a large proportion of elite athletes develop exercise-associated hyponatremia. (Hyponatremia is the medical term for low serum sodium).

In mild cases, hyponatremia causes confusion, cramps, and fogginess. In severe cases, it causes brain damage, seizures, and death. More than a few competitors have died from this hydration confusion.

The confusion also persists in the general population, but with more subtle consequences. I’m talking about the low energy, muscle cramps, tiredness, and brain fog of sodium deficiency.

Drinking Water and Sodium Deficiency

Drinking plain water exacerbates sodium deficiency. I see this happening in three main groups:

  1. Active people
  2. Those eating whole foods, low-carb, or keto diets
  3. Folks on fasting regimens

#1: Active people

Active people sweat a lot. It’s how we stay cool. And through that sweat, we lose both water and sodium. Both need to be replaced for optimal health, yet most people only actively focus on replacing water losses.

Then they wonder why their head’s pounding and they feel groggy or lethargic. Unmotivated, un-energetic, uninspired, staggering to the kitchen searching desperately for a pick-me-up.

It’s the lack of sodium! Sodium conducts nerve impulses. It facilitates communication between brain cells. Without it, you’re a zombie.

#2: Healthy eaters

When someone eliminates refined foods from their diet, they unwittingly eliminate their main dietary source of sodium. (Processed foods). The salt shaker has to step in to make up the shortfall.

Yes, cutting out pseudo-foods is a healthy move. But salt isn’t a pseudo-food. It’s an essential nutrient that most people are short on.

You also should know that low-carb and ketogenic diets, along with fasting regimens, increase sodium loss through urine. An interesting finding: taking sodium during the fast dampens the post-fast weight rebound.

Unfortunately, there’s a lot of bogus dietary advice out there, particularly in the world of keto. Instead of talking about sodium, it focuses on guzzling water to “stay hydrated”. But as we discussed, drinking plain water will only worsen low sodium symptoms. And no one wants to stick with a diet that makes them feel like crap.

How to Stay Properly Hydrated

Here are my two rules of healthy hydration:

  1. Drink to thirst
  2. Get enough electrolytes

Rule number one is self-explanatory. Don’t drink some arbitrarily-prescribed, one-size-fits-all amount of water. Just drink when you’re thirsty—that’s what thirst is there for.

Rule number two requires some calibration. Based on published evidence, daily baseline needs for sodium, potassium, and magnesium (the three electrolytes most people are low on) are:[*][*][*]

  • 4–6 grams of sodium
  • 3.5–5 grams of potassium
  • 400–600 mg of magnesium

Sodium requires the most calibration. The more you sweat, the more you cut carbs, the longer you fast, the more sodium you’ll need. Some folks will need 4 grams, others closer to 10 grams. Play around within these ranges until you find a sweet spot.

My hydration rules won’t help you lose weight, per se, but they will help you function your best and feel good while staying active.

Drinking Water to Lose Weight

When I think about helping people lose weight—and I think about it a lot—I don’t think much about drinking water. Although drinking water has small effects on satiety and metabolism, I don’t believe these effects are sufficient to promote sustainable weight loss or weight maintenance.

Plus there are risks to over-hydrating with plain water. It can tank your sodium levels and your energy along with it.

If you want to lose weight, focus on the fundamentals. Get enough sleep, be active every day, eat whole foods, manage your stress, don’t snack overnight, and prioritize meaningful relationships.

All of us can improve in one or more of these areas. And when we do, we’ll be amply rewarded.

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