What can you drink while fasting? There’s one simple answer: low- or no-calorie beverages.
This answer addresses frequently asked questions: Does water break a fast? No. What about diet soda, black coffee, or plain tea? They’re close enough to calorie-free for most fasting goals.
But there’s important 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, anyway. During fasting, glycogen depletion and increased sodium excretion can lead to greater fluid loss. The loss is greatest during the first part of a fast, 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.
Fasting has become another tool in optimization culture’s toolbelt. Eighteen hours is better than sixteen hours? Did that splash of cream ruin everything? Did five calories shut down autophagy? Did I eat three minutes too early?
It’s worth keeping some perspective: Humans’ ancestors experienced natural fluctuations in eating patterns, including occasional hunger. But they didn’t chase extreme fasting protocols or obsess over autophagy.
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 that doesn’t mean everyone needs a tightly controlled eating window to be healthy.
In fact, many researchers have suggested that fasting simply provides an easy framework that reduces how much — or how late — people eat. But when compared to conventional calorie restriction, the extra benefits of fasting aren’t always clear.
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 it.
If fasting is something you feel could make a meaningful impact on your health goals, keep reading. LMNT dives 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 drawing 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.
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:
- Insulin: This hormone is released in response to food intake, particularly carbohydrates but also protein. Insulin helps store energy in cells and promotes cell growth and repair.
- mTOR: This is a nutrient-sensing signaling pathway that is activated by amino acids, especially leucine and arginine. mTOR supports muscle and tissue growth. It also suppresses autophagy, a process that breaks down and recycles parts of damaged cells.
In tangible terms, these growth processes help 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 rise. 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 response — 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 matters.
Where insulin becomes more concerning is when the bigger system stops working well. Chronically high insulin often goes hand-in-hand with insulin resistance — a major driver of Type 2 diabetes. Dysregulation of mTOR is linked to aging and disease. 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 fast, 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 loss when it results in reduced overall energy intake. Fasting may also stimulate cellular recycling processes such as autophagy, 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 leucine 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.
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.
Can I drink water while fasting?
You not only can, but you should drink water to prevent symptoms of dehydration, especially since glycogen depletion and increased sodium excretion can lead to greater fluid loss during fasting. Just don’t overdo it, 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 drink electrolyte water while fasting. Fasting can increase sodium excretion, 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 calories and carbohydrates and shouldn’t disrupt the fast. Check the nutrition label for calories and macronutrients, and consider the goal of your fast.
Can I drink coffee while fasting?
Go for it. Black coffee can fit a zero-calorie fast. Most brews — sans creamers and flavors — only contain about 5 calories per cup, plus coffee contains loads of antioxidants and compounds that some laboratory studies suggest may influence autophagy. Adding fat or collagen provides calories and technically ends a strict fast, although small amounts may be compatible with some modified fasting approaches.
Can I drink tea while fasting?
Yep, this is the same principle as coffee. Only about 2 calories per cup here, plus lots of antioxidants.
Can I drink diet soda while fasting?
Yes, but consider a zero-calorie soda sweetened with stevia or monk fruit. Some studies suggest certain artificial sweeteners may affect gut microbiota, though evidence in humans is mixed.
Can I drink bone broth while fasting?
Unless you’re doing a modified fasting protocol, skip it. Bone broth contains about 50 calories and 9 grams of protein per cup, so it does break a fast.
Can I drink sparkling or lemon water while fasting?
Low- or zero-calorie sparkling water and water with a squeeze of lemon are fine to drink during a fast. Avoid sweetened sparkling water and those containing juice.
What Should You Not Drink While Fasting?
You should avoid drinks with any meaningful calories, sugar, or leucine- and arginine-rich protein while fasting.
Calories hide in a lot of common beverages. Here’s a quick list of drinks to avoid to help keep your body in fasting mode:
- Regular soda
- Fruit juice (even with “no sugar added” — fruit and fruit juices contain lots of natural sugar)
- Sugary sports drinks
- Milk, chocolate milk, and hot chocolate
- Smoothies
- Protein drinks
- Alcoholic beverages
- Most latte, cappuccino, mochaccino, and Frappuccino drinks
A Simple Framework: How Do You Know If a Drink Breaks Your Fast?
For a strict fast, stick with calorie-free beverages only. For less restrictive fasting approaches, whether a beverage is OK depends on your fasting goals and the calorie and macronutrient content of the specific drink.
When in doubt, check the nutrition label for calories and macronutrients and consider the goal of your fast. Or stick to water and electrolytes to help keep you hydrated throughout the day. Just make sure sugar doesn’t come along for the ride.
Fasting isn’t for everyone. Folks with diabetes — particularly anyone using insulin or medications that can cause hypoglycemia — should talk to their doctor before trying any kind of fasting. Pregnant or breastfeeding people and anyone with a history of disordered eating should also seek medical guidance before fasting.
This story was produced by LMNT and reviewed and distributed by Stacker.
