What can you drink while fasting?

While fasting, you can drink water, plain sparkling water, black coffee, unsweetened tea, and calorie-free electrolytes without breaking your fast. On a strict fast, avoid anything containing sugar, milk, cream, protein, or other calories. Small amounts of calories may be compatible with some modified fasting approaches, depending on the goal of the fast.

When people ask me what to drink while fasting, I have a simple response: low- or no-calorie beverages.

This two-word answer addresses most frequently asked questions: Does water break a fast? No. Diet soda, black coffee, or plain tea? Close enough to calorie-free for most fasting goals.

When I have more time to explain, I like to share the context behind that answer. Technically, consuming calories ends a zero-calorie fast. But fasting isn’t a switch that a calorie or two automatically flips off. For most practical goals like weight loss or metabolic health, small amounts of calories are unlikely to meaningfully disrupt the effects of fasting. Small amounts of fat or collagen in particular may have minimal metabolic impact for many people, though technically they provide calories and can activate some nutrient-sensing pathways.

You’ll want to drink something while you fast, anyways. During fasting, glycogen depletionOpens in a new tab and increased sodium excretionOpens in a new tab can lead to greater fluid loss. The loss is greatest during the first part of a fastOpens in a new tab, which may contribute to fatigue or headaches in some people. Replacing both fluid and electrolytes can help you stay hydrated and may help you feel better during a fast.

That’s the elevator spiel. And I’ve got one more…and it’s a hot take: many folks probably don’t need to fast.

Fasting has become another tool in optimization culture’s toolbelt. And like many things in that toolbelt, we’ve started majoring in the minors. Sixteen hours is better than eighteen hours? Did that splash of cream ruin everything? Did five calories shut down autophagy? Did I eat three minutes too early?

My opinion: Our ancestors experienced natural fluctuations in eating patterns, including occasional hunger. But they didn’t chase extreme fasting protocols. (They were too busy chasing their food… literally.)

Is there evidence that time-restricted eating can be a useful tool, particularly for people trying to lose weight or improve certain markers of metabolic health? Yes.

But does that mean everyone needs a tightly controlled eating window to be healthy? No.

In fact, many researchers have suggested that fasting simply provides an easy framework (people love a framework) that reduces how much — or how late — people eat. But when compared to conventional calorie restriction, extra benefits of fasting aren’t always clear.

The most generous interpretation of fasting is that it acts as a partial “exercise mimetic.”Opens in a new tab Both fasting and exercise can stimulate processes like autophagyOpens in a new tab. But exercise also makes us fitter across a broad range of metricsOpens in a new tab in ways fasting does not. So if the goal is to trigger some of the same cellular stress-response pathways, fasting may overlap with exercise but it isn’t a substitute for exercise (which actually improves your fitness).

Just keep that in mind. If a fasting routine makes it easier for you to eat well, maintain a healthy weight, or feel your best, great. Use the tool. If it makes your life harder without producing a meaningful benefit, you probably don't need to force it.

With that said, if fasting is something you feel could make a meaningful impact on your health goals, keep reading. I dive deeper into the mechanics of fasting, what breaks a fast, and what you can and can’t drink while fasting for best results.

How Does Fasting Work?

Fasting works by shifting your body from using incoming calories to instead draw more heavily on stored fuel. With no food coming in, your liver breaks down glycogen (the stored form of glucose) to help keep blood glucose steady. As that supply dwindles, your body leans harder on stored fat and begins producing more ketones for fuel.

To fully understand this, let me first share something important about eating. Eating supports “growth” processes in our bodies — cell growth, muscle growth, tissue development and repair, etc. These processes are supported by key hormones and enzymes, including:

1. Insulin: A hormone released in response to food intake, particularly carbohydrates but also protein. Insulin helps store energy in cells, and promotes cell growth and repair.
2. mTOR: A nutrient-sensing signaling pathway that is activated by amino acids, especially leucine and arginineOpens in a new tab. mTOROpens in a new tab supports muscle and tissue growth. Important to note, it also suppresses autophagyOpens in a new tab (a process that breaks down and recycles parts of damaged cells).

In tangible terms, these growth processes help us build bone, repair muscle tissue after a workout, and store energy for later use, among many other benefits.

Before insulin gets cast as the villain, let’s clear something up: If you have a human body and you consume food or drinks, your insulin will spike. That normal rise and fall helps shuttle nutrients where they need to go. It’s essential for a functioning body, not a metabolic emergency.

The goal of metabolic health isn’t to keep insulin as flat as possible. The amount and type of food you eat matter, as does your overall diet, activity, and metabolic health. For example:

• Carbohydrates generally trigger the greatest insulin responseOpens in a new tab — that’s a fact — but protein can stimulate insulin too.
• A large carbohydrate-heavy meal and something containing a gram or two of carbohydrate aren’t metabolically equivalent just because both contain carbs. Dose mattersOpens in a new tab.

Where insulin becomes more concerning is when the bigger system stops working well. Chronically high insulin often goes hand-in-hand with insulin resistanceOpens in a new tab — a major driver of type 2 diabetes. Dysregulation of mTOR, on the other hand, is linked to aging and diseaseOpens in a new tab.. That’s very different from treating every temporary rise in insulin after eating as something that needs to be avoided.

This is where fasting comes in. When you fastOpens in a new tab, insulin and mTOR signaling decrease, shifting the body away from growth pathways. During fasting, the body increasingly relies on stored fat for energy. Intermittent fasting may improve some metabolic measures and can support weight lossOpens in a new tab when it results in reduced overall energy intake. Fasting may also stimulate cellular recycling processes such as autophagyOpens in a new tab, although most evidence comes from laboratory or animal studies.

With insulin and mTOR in mind, it’s now easier to understand what breaks a fast.

What Breaks a Fast?

Strictly speaking, any food, drink, or supplement that contains calories ends a zero-calorie fast. Your exact metabolic response depends on the amount and type of calories consumed, with carbohydrates, proteins, and fats affecting insulin and nutrient-sensing pathways differently.

Carbs raise insulin the most (but remember: Dose matters). When you eat carbs, you digest those carbs into sugar, your blood sugar rises, and your pancreas releases insulin to store excess blood sugar in muscle, liver, and fat cells. Protein and fat can increase insulin too, but fat has the smallest effect.

Protein, on the other hand, activates mTOR; predominantly the amino acids leucineOpens in a new tab and arginine. Leucine is common in some protein sources like fish and eggs, but low in other proteins like collagen. Arginine is also found in protein-rich foods like fish, meat, and nuts as well as collagen.

For a strict zero-calorie fast, avoid caloric carbohydrates, proteins, and fats. Protein — particularly certain amino acids — can activate nutrient-sensing pathways such as mTOR. You can check out this article on what breaks a fastOpens in a new tab to go deeper.

But this article is on what to drink while fasting. So with this context out of the way, let’s jump into that.

What Can You Drink While Fasting?

While fasting, you can drink water, sugar-free electrolyte water, black coffee, plain tea, sparkling water, and most other drinks with few or no calories. Let me break down each individually and explain why.

Can I drink water while fasting?

You not only can, but you should drink water to prevent symptoms of Opens in a new tabdehydrationOpens in a new tab, especially since glycogen depletion and increased sodium excretion can lead to greater fluid lossOpens in a new tab during fasting. Just Opens in a new tabdon’t overdo itOpens in a new tab, listen to your body’s signals, and drink to thirst. This’ll keep most folks in the Goldilocks range of the “just right” amount of fluids.

There’s no universal amount of water everyone should drink while fasting. Your needs depend on your body, activity, and environment, so adjust rather than chasing an arbitrary ounce target:

• Follow your thirst: If you feel parched, drink until you’re not.
• Consider body size: Larger bodies typically need more water than smaller ones.
• Account for climate: Hot or humid conditions can increase your fluid needs.
• Adjust for activity: You may need more fluid on active or sweaty days than on rest days.

Can I drink electrolyte water while fasting?

You can absolutely drink electrolyte water while fasting. Fasting can increase sodium excretionOpens in a new tab, especially on longer fasts. How much more you need depends on your fasting duration, activity level, climate, and overall health — and since you won't be getting electrolytes through food like you normally would, it's worth paying attention to how you feel.

You’ll just want to be careful to read the labels. Some electrolyte drinks include quite a bit of sugar. Others contain only a few to zero calories and shouldn’t disrupt the fast. Check the nutrition label for calories and macronutrients and consider the goal of your fast.