Does Fasting Cause Dehydration? What to know about water and fasting
Does Fasting Cause Dehydration? What to know about water and fasting

Does Fasting Cause Dehydration? What to know about water and fasting

In the ever-evolving world of wellness, fasting is one of the few health strategies that seems to stand the test of time, even if it undergoes trendy new transformations once in a while. Still, though most people are familiar with how fasting works, a common question remains: Can I drink water while I’m fasting? And if so, how much? That’s what we’re exploring today, but first, let’s get on the same page about what fasting is and isn’t!

Fasting in a Nutshell: Why and how people fast

Historically, fasting has been used to improve physical and mental health, and has also been a core component of some religious practices, but it’s unclear exactly how far back this practice goes. Today, there are several types of fasting, each with its own unique parameters. For example:

  • Dry fasting: Often the kind of fasting you’re asked to do beginning the day before a surgical procedure: no food OR water.
  • Water fasting: Just like it says on the tin! You consume only water for a period of 2 to 3 days, and no calories.
  • Intermittent fasting: Quite popular in recent years. You eat each day’s calories within a scheduled window of 6 to 8 hours out of every 24.
  • Alternate-day fasting & 5:2 fasting: Unlike the typical one-off nature of water fasting, these forms allow normal eating only every other day, or a maximum of 5 days a week.

Thanks to how trendy fasting has become online, many folks turn to fasting for weight loss, but there are lots of other benefits to fasting, including an enhanced ability to focus. Keep that in mind the next time you have a deadline or an exam coming up — a fast might be more effective than the coffee and junk food you usually reach for!

Quick Warning: Things to consider before fasting

Like with any health-related behavior, talk to a health professional before you try any kind of fasting method. What’s more, you need to take special care if any of the following apply to you:

  • Prescription medications: Some meds need to be taken with food, for safety or for comfort. Don't mess around with your medication schedule for the sake of a fast — talk to your doctor!
  • Eating disorders: Fasting can trigger unhealthy behaviors in people with disordered relationships with food, or can be the first sign of disordered eating. Talk to a professional if you suspect this may apply to you.
  • Pregnancy & nursing: For the safety of yourself and your baby, never try fasting while pregnant or nursing, unless you’ve been instructed to by your doctor.

So? How much water should I drink while fasting?

How much water to drink during fasting depends entirely on which type of fasting you’re doing. Here are some basic guidelines:

Water fasting, Alternate-day fasting, 5:2 fasting

Since you’re going whole days without food experts recommend you consume 2 to 3 liters of water each day throughout the day. In particular, you’ll benefit most from mineral water, since it contains trace minerals you’d normally get from your food, albeit in much smaller amounts. If you’re doing alternate-day fasting or 5:2 fasting, this applies to you, too.

Intermittent fasting

You can continue to drink your usual amount of water, even during the fasting hours, without breaking your fast. Consider consuming more hydrating foods during the eating periods, and never ignore thirst during the fasting periods! Keep in mind, if you’re combining intermittent fasting with a keto diet, that you might need to up your water intake even more, and may need additional electrolytes. (Again, this is general advice, so talk to your doctor about your unique needs.)

Dry fasting

As its name suggests, you consume no food or liquids of any kind during this fast, even if you’re thirsty, which is why it shouldn’t be undertaken for prolonged periods without medical supervision. Ignoring the rules for this kind of fast can be dangerous, so for your safety, remember that different kinds of surgeries or tests require different levels of fasting, and only your doctor can tell you what to abstain from or how long.


And there you have it! If you’re about to embark on a fasting experiment for the first time, remember to pay close attention to how the fast is affecting your body, and don’t hesitate to abandon a fast if it’s causing you pain or discomfort. Sometimes it may just be dehydration and a sign to drink more water, but better hydration isn’t always the answer. Trust your gut (literally!) and you’ll be glad you did!

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