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How Much Water Should I Drink On Keto? (From Nutritionist)

Michael Garrico
Published by Michael Garrico
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: February 21, 2022

I’ve seen my fair share of people on keto diets during my years in the fitness industry.

Unfortunately, many don’t realize that they need to drink more water while on a low-carb diet like keto. Without proper hydration, such diets can lead to severe side effects.

I’ve spent dozens of hours researching how much water you should drink on a keto diet to help you prevent them. Here’s everything you need to know.

Quick Summary

  • We lose water and electrolytes in ketosis: that’s why you should drink more water than usual while on keto.
  • You can calculate your hydration needs based on your body weight.
  • Try eating water-rich foods, drinking rehydration drinks, and reducing your caffeine intake to keep hydrated.

How Much Water Should You Drink On Keto?

water in a plastic bottle and a woman with a salad bowl

The short answer is that you’ll need to drink more water than usual while on a keto diet. But you may be wondering what that means in practice.

One expert shares a general rule of thumb that you can follow [1]:

“[At the beginning of your keto diet], you should drink at least 2.5 liters of water or fluid per day to replace the amount lost in urine. Once you become keto-adapted, you should still consume a minimum of two liters of water daily in order to prevent dehydration and promote optimal metabolic health.” - Franziska Spritzler, RD, a certified diabetes educator 

So, you could try to drink 2.5 liters (~85 ounces) of water per day.

But you could also establish your individual hydration needs on a ketogenic diet based on your body weight.

That could be a better option than following a hard and fast rule that might be too general.

Use the following formula to calculate your ideal intake of water:

Your bodyweight x 75% = Ounces of water per day

Here are a couple of examples to illustrate how to use this formula to calculate your hydration needs:

  • If you weigh 120 pounds, you’ll need 90 ounces of water per day (120 x 0.75 = 90)
  • If you weigh 180 pounds, you’ll need 135 ounces of water per day (180 x 0.75 = 135)

As you can see, a 180-pound person needs significantly more water on keto than what the rule above suggested. That’s why I prefer following the formula over the general rule.

Once you’ve calculated your ideal fluid intake, all that’s left to do is stick to it.

But you might discover that that’s more difficult than it sounds. That’s why I’ll give you a few tips on how to stay hydrated below.

For now, let’s see why a keto diet increases your hydration needs in the first place.

Why Does My Body Need More Water On Keto?

man chugging a jug of water

In a nutshell, your body needs more water on keto because it loses water during ketosis.

Eating a keto diet means you’re keeping your carbohydrate intake low.

Low carb intake decreases levels of the hormone insulin. And low insulin encourages your body to start burning fat, i.e., enter ketosis [2].

Since keto is a low-carb, high-fat diet, your body will use fat instead of carbs for energy, but not entirely. It will also start using the glycogen stored in your body for this purpose.

Glycogen consists of carbohydrates that you’ve previously consumed but didn’t have to use because you were consuming carbs regularly [3].

It’s precisely thanks to this process — getting rid of stored carbs and rapid fat burning — that we lose weight on keto.

But we also lose water during this process because each gram of glycogen is bound to 3 to 4 grams of water [4]. This is often referred to as our water weight [5].

On top of losing fluid, we also lose sodium and potassium, electrolytes that regulate fluid levels in your body and maintain fluid balance [6].

That’s why you need to increase your fluid intake while on a keto diet. Otherwise, you risk dehydration.

Symptoms And Prevention Of Dehydration

woman caressing her throat and a woman in headache

The first step in preventing dehydration is knowing how to recognize it.

Symptoms of mild dehydration include [7]:

  • Thirst 
  • Dry, sticky mouth
  • Dark, yellow pee
  • Dry skin
  • Headaches
  • Muscle cramps

Below are the symptoms of severe dehydration:

  • Dizziness
  • Rapid heartbeat
  • Rapid breathing
  • Sunken eyes
  • Nausea
  • Fatigue

You might have noticed that many of these symptoms are similar to those caused by the flu.

They’re fairly common in people on a ketogenic diet, which is why they’re often called keto flu symptoms.

It’s not entirely clear what causes keto flu, but it might be linked to dehydration, and that’s why it’s recommended that you drink water to prevent it [8].

However, preventing dehydration isn’t always as simple as it sounds. It’s not just about drinking water, either.

Step #1: Change Your Mindset

woman pointing at her head

You need to forget the famous 8x8 rule because there’s little to no scientific evidence that proves that we should drink eight glasses of water per day [9].

The entire myth started when the Food and Nutrition Board recommended that average adult males consume about 2,500 ml (~84 ounces) of water per day [10].

However, they didn’t support this recommendation with scientific studies. Nor did the later studies support this recommendation.

That’s why it’s better to use the 75%-formula to calculate your ideal water intake while on a low-carb diet. It will be more accurate than the 8x8 rule.

Step #2: Make A Habit Out Of Drinking Water

You can do so by setting your alarm to go off every half an hour or by keeping a water bottle near you at all times.

Both strategies will help you hydrate on auto-pilot.

First, you’ll be reminded to take regular sips of water. After a while, you won’t need reminders anymore.

Downsides Of Overhydration

woman holding her neck in pain

Our main concern with low-carb diets is dehydration. However, you can still overhydrate even if you’re on a ketogenic diet.

Overhydration isn’t good either. Drinking too much water can lead to a state called hyponatremia, which occurs when your blood sodium levels are too low [11].

Low sodium levels are common with folks on a keto diet for two reasons: 

  • A ketogenic diet implies that we’re cutting out processed foods and salty carbs (i.e., consuming less sodium than usual).
  • We lose more sodium through urine in ketosis [12].

So, the problem is that you already don’t have enough sodium while on keto.

Drinking only sodium-free water or simply too much water will further dilute your sodium levels and cause symptoms of hyponatremia, such as [13]: 

  • Muscle weakness, spasms, and cramps
  • Fatigue
  • Nausea
  • Irritability
  • Headaches
  • Seizures
  • Coma

Luckily, there are things you can do to prevent hyponatremia even while on a low-carb diet.

For one, you can watch your sodium consumption. Try eating more healthy sodium-rich foods, such as buttermilk, cottage cheese, or canned vegetables [14].

Of course, you don’t want to overdo it with sodium-rich foods since you’re still trying to lose weight. And too much sodium may prevent weight loss and beat the purpose of a keto diet [15].

Other Ways To Hydrate On A Keto Diet

bowl of broccoli and a woman drinking water after jogging outdoors

Staying hydrated doesn’t only depend on your water intake. There are other things you can and should do. We’ll go through the three most important ones below.

1. Eat Water-Rich Foods

The problem with a keto diet is that it limits our consumption of various fruits and vegetables.

The lack of fruits and vegetables may decrease your fiber intake and lead to dehydration   [16],[17].

For example, most keto diets don’t allow you to consume bananas and peas. And both contain a lot of water.

So, not consuming them increases the risk of dehydration.

To prevent it, try replacing “forbidden” water-rich foods with those you can consume.

For example, you could eat broccoli instead of peas and berries instead of bananas [18].

2. Lower Your Caffeine Intake

man holding up a mug and his thumbs down

Health experts have long suspected that caffeine has dehydrating effects. However, recent studies show that you can drink coffee in moderation without experiencing any side effects [19].

Still, we know that caffeine has a diuretic effect and makes you pee more often [20].

So, drinking coffee on your keto journey may make you lose more water. You should check our list of the 5 best keto-friendly pre-workouts.

That’s why you should cut caffeine on keto to keep your hydration levels in a healthy range.

3. Try Rehydration Drinks

Rehydration drinks are water drinks or drinks that contain electrolytes [21].

They’re usually used after workouts, but you can use them to hydrate your body while on keto.

Of course, you should choose only keto-friendly rehydration drinks.

For example, you should choose drinks that contain little to no carbohydrates. Otherwise, all your effort so far will have been for nothing.

FAQs

Can Not Drinking Enough Water on Keto Stall Weight Loss?

Yes, not drinking enough water on keto can stall weight loss. But that’s true for any type of diet since dehydration slows down your metabolism and triggers food cravings [22].

Can You Keep Hydrated On Keto?

As a low-carb diet, keto increases your hydration needs. So, you have to adapt to those new needs by consuming more fluids and water-rich foods.

You can also try rehydration drinks if you notice or just want to prevent the side effects of dehydration.

Keep in mind that keto-induced weight loss may lead to loose skin. To keep your body tight, consider using these keto-friendly protein powders. They can help you reclaim your muscles and look your best.


References:

  1. https://www.popsugar.co.uk/fitness/How-Much-Water-Should-You-Drink-Keto-45309016
  2. https://www.healthline.com/nutrition/what-is-ketosis 
  3. https://www.healthline.com/nutrition/how-long-does-it-take-to-get-into-ketosis 
  4. https://www.medicalnewstoday.com/articles/323544
  5. https://www.puregym.com/blog/water-weight-what-is-it-and-why-does-it-matter/ 
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5858534/ 
  7. https://www.webmd.com/a-to-z-guides/dehydration-adults 
  8. https://www.health.harvard.edu/blog/what-is-keto-flu-2018101815052 
  9. https://journals.physiology.org/doi/full/10.1152/ajpregu.00365.2002 
  10. https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1753-6405.2012.00866.x 
  11. https://www.mayoclinic.org/diseases-conditions/hyponatremia/symptoms-causes/syc-20373711
  12. https://www.carbmanager.com/article/xtqunbeaacaacgdw/importance-of-electrolytes-on-keto/ 
  13. https://www.mayoclinic.org/diseases-conditions/hyponatremia/symptoms-causes/syc-20373711 
  14. https://www.ucsfhealth.org/education/guidelines-for-a-low-sodium-diet 
  15. https://www.healthline.com/nutrition/does-sodium-make-you-fat
  16. https://www.everydayhealth.com/dehydration/diets-that-may-contribute-to-dehydration
  17. https://www.healthyfood.com/ask-the-experts/low-carb-fibre-intake/ 
  18. https://www.everydayhealth.com/ketogenic-diet/foods-you-can-t-eat-on-keto-and-what-to-choose-instead/ 
  19. https://www.healthline.com/nutrition/does-coffee-dehydrate-you 
  20. https://www.dripdrop.com/blog/diuretics/is-coffee-a-diuretic 
  21. https://www.sharecare.com/health/non-alcoholic-drinking/what-rehydration-drinks
  22. https://www.garciaweightloss.com/blog/10-foods-cause-weight-loss-plateau/

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