What Can You Drink During Intermittent Fasting? Complete Guide

One of the most common questions people ask when starting intermittent fasting is simple: what can I drink? The answer matters because the wrong beverage can break your fast, trigger an insulin response, and undermine the metabolic benefits you are working toward.

The good news is that you have more options than you might think. This guide covers every common beverage, explains the science behind why certain drinks break a fast and others do not, and gives you practical guidelines you can follow with confidence.

What does "breaking a fast" actually mean?

Before diving into specific beverages, it helps to understand what we mean by breaking a fast. There are two ways to think about this, depending on your goals.

Metabolic fasting is about keeping insulin low and fat oxidation high. From this perspective, anything that triggers a meaningful insulin response breaks your fast. Small amounts of calories (under 10 to 15) from fat or certain compounds may not significantly impact insulin, so some flexibility exists.

Strict fasting means consuming zero calories. This is relevant if you are fasting for autophagy (cellular cleanup), gut rest, or specific medical protocols. In strict fasting, even black coffee is debatable because it contains trace organic compounds, though most researchers still consider it acceptable.

For most people practicing intermittent fasting for weight loss and general health, the metabolic definition is the practical standard. That is the framework we will use throughout this guide.

Water: your primary fasting beverage

Water is the foundation of any fasting protocol. It contains zero calories, does not affect insulin, and is essential for every bodily function.

Plain water is always safe. Drink it freely throughout your fast. Most people underestimate how much water they need, especially during fasting when they are not getting water from food.

Sparkling water (plain, unflavored) is also fine. The carbonation does not affect your fast. Brands like San Pellegrino, Perrier, or any plain seltzer are all acceptable. Just check the label -- some flavored sparkling waters contain sweeteners or calories.

Mineral water is excellent during fasting because it provides electrolytes (sodium, magnesium, calcium) that help prevent the headaches and fatigue some people experience during longer fasts.

Water with lemon or lime is a common question. A thin slice or small squeeze of lemon adds roughly 1 to 3 calories. This amount is negligible and will not meaningfully affect insulin or fat burning. If lemon water helps you drink more fluids and stick with your fast, use it.

Water with apple cider vinegar (1 to 2 tablespoons) contains minimal calories and has been shown in some studies to improve insulin sensitivity. It will not break your fast. However, always dilute it well and do not drink it on a completely empty stomach if you have acid reflux.

How much water should you drink?

Aim for at least 2 to 3 liters during your fasting window, more if you exercise or live in a warm climate. Dehydration mimics hunger, so staying well-hydrated makes fasting significantly easier. Many people find that a large glass of water first thing in the morning eliminates the sensation of hunger entirely.

Coffee: the fasting community's best friend

Black coffee is considered safe during intermittent fasting by virtually every expert and researcher in the field. A standard cup of black coffee contains roughly 2 to 5 calories, primarily from trace oils and proteins in the beans. This amount does not trigger a meaningful insulin response.

Beyond being permissible, coffee actively supports fasting in several ways:

Appetite suppression. Caffeine is a mild appetite suppressant that can make the last few hours of a fast feel effortless. Research published in the International Journal of Food Sciences and Nutrition found that coffee consumption reduces perceived hunger.

Enhanced fat oxidation. Caffeine increases the rate at which your body burns fat. A study in the American Journal of Clinical Nutrition found that caffeine can boost metabolic rate by 3 to 11 percent.

Mental clarity. Many fasters report that black coffee during the morning hours produces a state of sharp mental focus that is difficult to replicate while fed.

What about additives?

This is where things get nuanced:

Black coffee (no additives): Does not break your fast. Drink freely.

Coffee with a splash of heavy cream (10 to 15 ml): The fat content is roughly 5 to 8 calories. Pure fat has minimal insulin impact. Many fasting experts, including Jason Fung, consider this acceptable for weight loss purposes. However, it does technically break a strict fast.

Coffee with milk: Even a small amount of milk (30 ml) adds 5 to 15 calories plus lactose, which is a sugar that triggers insulin. This will break your fast for most practical purposes.

Coffee with sugar: Breaks your fast immediately. Even a single teaspoon of sugar triggers a substantial insulin response.

Bulletproof coffee (coffee with butter and MCT oil): Contains 200+ calories. This absolutely breaks your fast, despite claims from some proponents. While it keeps you in ketosis, it halts autophagy and provides your body with external fuel rather than forcing it to burn stored fat.

Coffee with artificial sweeteners: This is controversial. Some studies suggest that artificial sweeteners like sucralose and aspartame can trigger insulin responses through taste receptors, while other studies find no effect. If you want to play it safe, avoid them during your fast.

How much coffee is too much?

Three to four cups per day is generally considered safe for most adults. Be mindful of caffeine's half-life (roughly 5 to 6 hours) and stop drinking coffee by early afternoon to protect your sleep quality. Poor sleep undermines both fasting benefits and weight loss.

Tea: a versatile fasting companion

All plain teas are safe during intermittent fasting. Like coffee, they contain negligible calories and offer additional health benefits.

Green tea is particularly beneficial during fasting. It contains catechins (especially EGCG) that enhance fat oxidation and support autophagy. A meta-analysis in the International Journal of Obesity found that green tea catechins significantly increase fat burning, particularly during exercise.

Black tea provides caffeine (roughly half the amount of coffee) along with theaflavins, which have antioxidant and anti-inflammatory properties.

Herbal teas (peppermint, chamomile, rooibos, ginger) are calorie-free and safe during fasting. Peppermint tea is especially popular because it can reduce the sensation of hunger. Ginger tea may help with any nausea that occasionally occurs during longer fasts.

Oolong tea falls between green and black tea in terms of oxidation and caffeine content. It has been specifically studied for its fat-burning properties, with research suggesting it increases energy expenditure by about 2.9 to 3.4 percent.

Matcha is concentrated green tea powder and is safe during fasting if consumed without milk or sweeteners. It provides a gentler caffeine release than coffee due to the presence of L-theanine, which promotes calm alertness.

Tea rules during fasting

No sugar, honey, or sweeteners
No milk, cream, or plant-based milks
Plain tea bags or loose-leaf tea only
Flavored teas are fine as long as they contain no added sugars (check ingredients)

Electrolytes: often necessary, sometimes overlooked

Electrolyte balance is one of the most important and most neglected aspects of fasting. When you fast, your body excretes more sodium through urine (a consequence of lower insulin levels). This sodium loss pulls potassium and magnesium along with it.

Symptoms of electrolyte depletion include headaches, dizziness, fatigue, muscle cramps, and irritability. Many people blame these symptoms on fasting itself, when the real culprit is simply inadequate electrolytes.

What to use:

Salt (sodium chloride): A pinch of salt in water or under the tongue is the simplest remedy. Pink Himalayan salt works, but regular table salt is equally effective.
Electrolyte powders/tablets without calories or sweeteners: Products like LMNT, Hi-Lyte, or similar zero-calorie electrolyte supplements are designed for fasting. Look for sodium, potassium, and magnesium with no sugar or maltodextrin.
Magnesium supplements: Magnesium citrate or glycinate taken with water will not break your fast and can help with sleep quality and muscle relaxation.

What to avoid:

Sports drinks (Gatorade, Powerade) -- loaded with sugar
Electrolyte products with maltodextrin, dextrose, or sugar
Coconut water -- contains natural sugars and significant calories

Diet soda and zero-calorie drinks

This is one of the most debated topics in the fasting community. Diet sodas contain zero calories, but they contain artificial sweeteners that interact with your body in complex ways.

The concern is the cephalic phase insulin response. When your tongue detects sweetness, your brain may signal your pancreas to release insulin in anticipation of incoming sugar. Some studies have demonstrated this effect with sucralose and saccharin, while others have not found it.

The practical verdict: If weight loss is your primary goal, an occasional diet soda during your fast is unlikely to significantly impact results. However, if you are fasting for maximum metabolic benefit, autophagy, or gut rest, avoid artificial sweeteners.

There is also a behavioral argument: sweet-tasting beverages during a fast can intensify cravings and make the fast feel harder. Many people find that eliminating all sweet tastes during fasting makes hunger management much easier.

Bone broth: technically breaks your fast

Bone broth contains 30 to 50 calories per cup, along with protein (amino acids) that trigger an insulin response. It breaks your fast, period.

That said, some longer fasting protocols (24 to 48 hours) use bone broth strategically as a bridge. The calories are minimal, the electrolytes are helpful, and for some people, a cup of bone broth is the difference between completing a 36-hour fast and abandoning it at hour 20.

If you are doing daily 16:8 fasting, bone broth during your fasting window is unnecessary. Save it for your eating window. If you are attempting extended fasts, it can be a useful tool -- just understand that you are trading strict fasting for sustainability.

Beverages that definitely break your fast

For clarity, here are common beverages that unambiguously break a fast:

Juice (any kind) -- high in sugar and calories
Smoothies -- calorie-dense regardless of ingredients
Milk or plant milks (oat, almond, soy) -- contain calories, sugars, and/or proteins
Protein shakes -- designed to trigger an insulin response
Alcohol -- contains calories and disrupts liver metabolism
Soda (regular) -- pure sugar
Kombucha -- contains sugar and calories, even the low-sugar varieties
Energy drinks (most varieties) -- check labels carefully; many contain sugar or calories

Practical guidelines by fasting goal

If your goal is weight loss

You have the most flexibility. Black coffee, plain tea, water, and zero-calorie electrolytes are your staples. A splash of cream in coffee or a squeeze of lemon in water will not meaningfully affect your results. Occasional diet soda is unlikely to derail progress. Focus on consistency with your fasting window rather than perfection with every sip.

If your goal is metabolic health and insulin sensitivity

Stick to water, plain coffee, and plain tea. Avoid artificial sweeteners, as even the possibility of an insulin response is worth avoiding when insulin management is your primary objective. Electrolyte supplements without sweeteners are fine.

If your goal is autophagy and longevity

Be the most strict. Water and plain tea are your safest options. Black coffee is likely fine based on current research, but the science is less clear than for water and tea. Avoid everything else during your fasting window.

Tips for staying hydrated and comfortable

Start your day with a large glass of water. Rehydrating after sleep sets a positive tone and often eliminates perceived hunger.
Alternate between warm and cold beverages. Warm tea in the morning, cold sparkling water in the afternoon -- variety makes fasting more sustainable.
Keep a water bottle visible. You will drink more when water is in front of you. This is simple behavioral design.
Add a pinch of salt to your morning water. This addresses the most common cause of fasting headaches before it starts.
Prepare your beverages the night before. Cold brew coffee, iced tea, or infused water ready to go in the morning removes friction and makes your fast feel easy.
Track your fasting window with an app like FastBreak so you know exactly when you can eat and when to stick with approved beverages.

The bottom line

Intermittent fasting does not mean going thirsty. Water, black coffee, and plain tea are your foundation -- they support hydration, energy, and fat burning without compromising your fast. Electrolytes are not just allowed but often necessary, especially for fasts longer than 16 hours.

Beyond these basics, the degree of strictness depends on your goals. For most people pursuing weight loss and general health, a small amount of flexibility with beverages will not make or break results. What matters far more is the consistency of your fasting window and the quality of food you eat during your eating window.

Keep it simple, stay hydrated, and let the fast do its work.