How Much Water Do We Need for Weight Loss?

Today we are going to scientifically answer the question, “How much water should we be drinking to lose weight?”

Especially on these hot summer days.

To begin, let’s talk about the elephant in the room.

Did you know that there is a surprising lack of scientific study in this area of hydration?  To think that water, the most important nutrient that we need, is very poorly understood.

It’s true.

The current recommendations are pretty varied and poorly scrutinized or substantiated by science.

For instance, the advice to drink 8, 8oz glasses of water has absolutely no scientific background for such a claim and we don’t even know where it came from.

The US Recommendations and WHO recommendations are based on average water intake from people who filled out surveys, plus data on average urine outputs.

Basically like, “well, how much do normal people drink?  And how much do they pee out?”

We can measure dehydration person to person, but we need blood and urine to do so.  And that individual hydration data is not adequate to broadcast to the population level.  

Which means, just because you need 1400 mL to have normal osmolality in your blood, someone else might need 1900 mL.

Osmolality measures the electrolyte-water balance in our body fluids.

All this to say, that if you see someone or an article with a very specific prescription for water intake, know that someone made it up with any science to back it up.

And yet, we still have to put out a number, right!?

So, the number was chosen for women was 11 cups or 88 oz or 2.6 L of fluid that must pass our lips per day by the National Academy of Medicine

That’s a ton!

But here’s the good news: 20% of the fluid that must pass our lips each day is from food. 

Food like bananas, lettuce, or our quinoa cooked in water, etc.

Which is about 2 cups/16 oz/480L per day that we technically don’t have to drink, but will get through food.

Confusingly, some articles will talk about total fluid. Some articles will talk about liquids that we drink. Some don’t understand enough to even know that there is a difference.

So the current recommendation is basically 9 cups/ 72 oz/ 2 L of liquids that we should drink above and beyond what we eat per day.

Guys, that’s a lot of liquid. 

Guess how much the average, normally hydrated person urinates in a day?

1500 mL/day.  On average we urinate 6-7 times per day.

The average intake of people before we started telling everyone to drink more: 1200-1600 mL

So, is 2000 mL of water per day really necessary? Probably not.

So let’s zero in on what we here in this group really care about: how many cups of water should I drink to lose weight?

Ok, the way that water can help with weight loss can come from two basic questions.

1. Can it help you eat less calories?

2. Can it directly increase metabolic rate or fat burning?

So, for #1, yes, drinking water with meals can help you feel fuller faster.  It can help you eat less at that meal.

I know from the Freese Method, we use fluids as very helpful and successful bridges between meals to help us not snack.

And those bridges, when done correctly, are incredibly effective and help us lose weight because we essentially eat less sugar and stay in our Green Zone longer.

But what about fat-burning? Can water help you actually burn more fat?

In 2016, a scientist  named Simon Thorton noticed in other people’s research studies, when rats increased their water intake, they lost weight.

He reviewed these rat studies and found that when rats drank plenty of water, their mitochondria increased energy production.  This, in rats, sometimes showed up as an increase in fat-burning. 

So he says that mechanistically, this should be true in humans. Meaning, it works out logically in his head.  It works out in rats in a lab.  So he theorizes that this should cross nicely into humans in real life situations. That humans should be able to increase their mitochondrial activity in their fat cells and burn more fat thus leading to weight loss.

But, we don’t know.  We haven’t proven this in humans at all.

Nonetheless, this study is constantly being cited by all the articles on weight loss and hydration that really push high water prescriptions.

But ladies, it’s just rats.  It’s just a hypothesis.  It hasn’t been proven. But we all walk around like it's a fact.

Here is another pesky myth about hydration that we can clear up:

Myth: Caffeinated fluids are diuretics and don’t count towards your fluid needs. 

Wrong.  We have good science that disproves this.  All fluids count. Milk, coffee, tea, RedBull, all good.

Another myth is that by the time you are thirsty you are already dehydrated.

Wrong.

Scientifically, we can measure that thirst can start at 2% plasma osmolality and dehydration starts at 5%. 

So if you’re thirsty, just have a cup of water and don’t fret. You’re ok.

So, how much should we drink?

Well not 8, 8 oz cups of water.  They tested this out in 2017 with overweight adolescents and it didn’t do a thing, nobody lost weight. But maybe that was because they couldn’t reach those goals.

The other elephant in the room is that these high water recommendations are hard to meet in normal life.

Here’s my recommendation:

Drink at least 6 cups or 1500 mL/day of fluid, no matter what type, excluding alcohol.

And don’t go too much over 9 cups or 2L per day in drinks.

If you drink too much, you’ll lose too much sodium. If you lose too much sodium, your body will turn on insulin to tell your kidneys to reabsorb the sodium from your urine.  In my experience, this also leads to a lot of cramping in your muscles.

Here’s the best way to get the most out of water and fluids.

Drink one cup with each meal to help you swallow your food, enhance digestion, and feel full.

Then drink 1-2 cups between meals so you don’t snack.  

So that can be one cup of green tea between breakfast and lunch, 1-2 cups of coffee or tea or water or whatever between lunch and dinner. Then maybe a decaf tea after dinner to help you from snacking.

You do not need to spend a weird amount of energy on sipping water all day.  You do not need to carry a water bottle around all the time.  Unless, that water bottle keeps you from nibbling on Hot Tamales and other snack foods.

You do need to drink more water if you are very hot, very sweaty, or both.  If you can, add a pinch of salt to your water if you are in a hot environment and you are sweating a lot.  You need to replenish your electrolytes, not just your fluids in that type of environment.

The power in water for weight loss as of now is to help you feel full and to keep naughty things out of your mouth.  So use it that way.  Just drinking 1 mL/kcal or 1 oz/kg of body weight isn’t going to magically make you thinner.

Alright everyone, that was super fun, I hoped this helps ease everyone’s anxiety around water and fluids.

Remember, you have what it takes to lose weight, you just need to repair your metabolism first!