What can you drink when fasting?

What can you drink when fasting? The short answer is water, black coffee, plain tea, and sparkling water. These drinks have zero calories and won’t spike your insulin, so your body stays in fat burning mode.

But here’s where it gets tricky. Some drinks that look safe can actually break your fast without you knowing. And some drinks that seem off limits might actually help you fast longer.

Let’s break down exactly what works and what doesn’t.

Does water break a fast?

No. Water is the safest drink during any fast. It has zero calories, won’t trigger an insulin response, and keeps you hydrated.

Your body actually loses more electrolytes during fasting because of the metabolic changes happening inside you. Drinking water helps offset this loss and prevents common fasting side effects like headaches and dizziness.

Research shows about 20% of your daily fluid intake normally comes from food. When you fast, you lose this source, so you need to drink more water than usual.

Add a squeeze of lemon if you want flavour. Lemon water has very little sugar and a low glycemic index, so it won’t cause a sudden rise in blood glucose. Just skip any sweeteners.

Does black coffee break a fast?

No. Black coffee does not break a fast.

A standard cup of black coffee has only 2 to 5 calories. This is too small to trigger the insulin release that would end your fasted state. Research protocols for intermittent fasting often allow black coffee during fasting windows for this exact reason.

A 2021 study from Oklahoma State University found that drinking black coffee after a 10 hour fast did not affect triglyceride or glucose levels compared to drinking water. Ten adults completed the study and showed no difference in metabolic response between the two groups.

Coffee can actually help your fast in a few ways. Caffeine boosts your metabolic rate and increases fat burning. It also suppresses appetite, making fasting easier. Research published in The New England Journal of Medicine notes that caffeine may support ketone production and fat oxidation during fasting.

The catch? You need to drink it black. No sugar. No milk. No cream. No flavoured syrups.

Even a splash of milk contains calories, carbs, and proteins that can break your fast. Heavy cream has fewer carbs than regular milk but still contains calories that technically end a strict fast.

Does tea break a fast?

Plain tea does not break a fast. Both caffeinated and non caffeinated teas have very few calories and don’t contain significant amounts of glucose, protein, or fat.

Clinical trials on time restricted eating allowed tea consumption during fasting windows and still showed benefits like improved glucose control, reduced weight, and lower blood pressure.

Green tea is especially good during fasting. It contains antioxidants called catechins that help fight stress in your cells. One compound called EGCG has been linked to boosting metabolism and promoting fat burning.

Herbal teas are also fine. Studies on herbal tea show that drinking it during fasting doesn’t take away from fasting’s benefits.

Just keep your tea plain. Adding honey, sugar, or milk turns a fasting friendly drink into a fast breaker.

Does sparkling water break a fast?

No. Sparkling water is calorie free and won’t break your fast.

Research shows the bubbles in carbonated water can actually help reduce feelings of hunger or an empty stomach. This makes sparkling water a good option when you’re struggling through a fasting window.

Plain sparkling water is safe. Watch out for flavoured versions though. Some sparkling waters labelled with natural flavours can contain hidden additives that might interfere with fasting benefits.

Stick to plain sparkling water or add a squeeze of fresh lemon or lime for flavour.

Do diet sodas break a fast?

This one is tricky. Diet sodas have zero calories, but they might still interfere with your fast.

Research suggests that artificial sweeteners can trigger an anticipatory insulin response. When you taste something sweet, your body expects sugar to arrive and releases insulin to prepare. This can reduce fat burning even though no actual sugar entered your system.

A study published in Nature found that artificial sweeteners like saccharin can lead to glucose intolerance by disrupting the balance of gut bacteria. Regular consumption of these sweeteners has been linked to changes in the gut microbiome and potentially negative impacts on glucose metabolism.

One randomized crossover study found no cephalic insulin response when tasting aspartame, while glucose caused an early rise in insulin. But other research shows habitual use of artificial sweeteners can affect insulin resistance over time.

If your goal is strict fasting for metabolic health, skip the diet soda. The sweet taste can also trigger cravings, making your fast harder to stick to.

Does bone broth break a fast?

Yes, technically. Bone broth contains calories, usually around 30 to 50 per cup and about 5 to 10 grams of protein.

But bone broth sits in a grey area. Many fasting experts allow it during longer fasts because the calories are so low and it provides electrolytes like sodium, potassium, and magnesium that can prevent fasting side effects.

A clinical trial published in 2025 studied 100 adults with obesity who followed a bone broth diet combining intermittent fasting with bone broth consumption. Participants saw improvements in body weight, body composition, and metabolic markers.

If you’re doing a strict water fast for autophagy and cellular repair, bone broth will interrupt that process. But if your goal is fat loss and you’re struggling with a longer fast, bone broth can help you get through it without overeating later.

Bone broth makes an excellent way to break a fast too. It’s gentle on your digestive system and provides easily absorbed nutrients.

Do artificial sweeteners break a fast?

Most artificial sweeteners are zero calorie, so they don’t break a fast in the traditional sense. But they can affect your body in ways that work against your fasting goals.

Here’s what the research shows for common sweeteners.

1. Stevia and monk fruit don’t raise blood sugar or insulin levels in most people. These are the safest options if you need sweetness during a fast.
   
2. Aspartame has no effect on blood glucose, insulin, or gut hormones according to multiple studies.
   
3. Sucralose is more controversial. One review found 33 studies confirming sucralose has no impact on glucose concentrations. But another study found regular sucralose consumption can affect insulin response and glucose levels in healthy young adults.
   
4. Sugar alcohols like xylitol and sorbitol contain calories (about 2.4 calories per gram) and can cause a rise in glucose and insulin levels if you consume too much.
   

The bigger issue? Artificial sweeteners can increase hunger ratings and make you crave more sugar. This can make sticking to your fast harder and lead to overeating when your eating window opens.

What about apple cider vinegar?

Apple cider vinegar does not break a fast. It has almost no calories and has been linked to improved digestion and blood sugar control.

To use it during fasting, mix 1 to 2 teaspoons with water. The citric acid can help stimulate stomach acid production, which may improve digestion when you break your fast.

Always dilute apple cider vinegar. Drinking it straight can damage your tooth enamel because of its high acidity.

What drinks will definitely break your fast?

These drinks contain calories and will end your fast immediately.

1. Fruit juice. Packed with sugar and calories that spike your blood glucose fast.
   
2. Milk. Contains lactose (a natural sugar) plus protein and fat.
   
3. Smoothies. Usually high in calories from fruit, milk, and other ingredients.
   
4. Alcohol. Contains sugar, carbs, and calories. Save it for your eating window.
   
5. Sports drinks like Gatorade. Even zero calorie versions often contain sweeteners that can trigger insulin.
   
6. Coffee with milk, cream, or sugar. That splash of milk or teaspoon of sugar pulls your body out of fasting state within minutes.
   
7. Flavoured coffees and lattes. These typically contain hidden sugars and lots of calories.
   

Complete fasting drinks list

Safe during fasting.

1. Water (plain or with lemon)
2. Sparkling water (plain)
3. Black coffee
4. Espresso
5. Plain green tea
6. Plain black tea
7. Herbal tea (unsweetened)
8. Apple cider vinegar (diluted)

Use with caution.

1. Diet soda (zero calories but may trigger insulin response)
2. Flavoured sparkling water (check for hidden additives)
3. Stevia sweetened drinks (generally safe but may increase cravings)
4. Bone broth (will break strict fast but may help with longer fasts)

Avoid during fasting.

1. Fruit juice
2. Milk (any type including almond, oat, soy)
3. Smoothies
4. Alcohol
5. Sports drinks
6. Coffee with cream or sugar
7. Sweetened tea
8. Soft drinks

How much can you drink during fasting?

Aim for 2 to 3 litres of fluids each day during fasting according to research published in Global Advances in Health and Medicine.

Most people can use their thirst signals to guide intake, but when you’re fasting you lose fluids you’d normally get from food. It’s easy to get dehydrated without realising.

A good rule is to drink water throughout your fasting window. If you drink coffee or tea, don’t count these toward your water goal. Coffee is a diuretic, meaning it increases urination and can cause dehydration if you rely on it alone.

Consider adding electrolytes to your water if you’re doing longer fasts. Your body loses more electrolytes during fasting, and low levels can cause headaches, muscle cramps, and fatigue. Use versions without sweeteners or additives.

FAQ

Will one sip of coffee with milk break my fast?

Even a small amount of milk contains calories and protein that can trigger an insulin response. One tablespoon of cream adds about 50 calories and 3 grams of fat. Your body can shift from fasted to fed state within 15 minutes of consuming these calories. For a strict fast, stick to black coffee.

Can I add cinnamon to my coffee while fasting?

Yes. Cinnamon has almost no calories and research suggests it may improve glucose metabolism and insulin sensitivity. It won’t break your fast.

How many calories will break a fast?

Most experts agree that staying under 10 calories won’t significantly impact your fast. Some allow up to 50 calories. Black coffee falls well under this at 2 to 5 calories per cup. Anything over 50 calories will likely trigger enough of an insulin response to end the metabolic benefits of fasting.

Does the type of coffee matter for fasting?

No. Black drip coffee, espresso, French press, cold brew, and instant coffee are all fine during fasting as long as you don’t add anything with calories. The brewing method doesn’t affect whether coffee breaks your fast.

Can I drink coffee all day while fasting?

Limit yourself to 3 to 4 cups per day. Too much caffeine can cause dehydration, jitters, and sleep problems. Coffee increases gastric acid secretion by up to 80% which can irritate your stomach when empty. Space out your cups and drink plenty of water between them.

Will lemon water break my fast?

No. Lemon juice has very little sugar and a low glycemic index. A squeeze of lemon in your water adds negligible calories and won’t cause a significant rise in blood glucose. It can make water more enjoyable during fasting and provide some vitamin C.

Can I have coconut oil in my coffee while fasting?

Coconut oil contains calories, so it technically breaks a strict fast. A tablespoon has about 120 calories. However, some fasting approaches like bulletproof coffee allow fats because they don’t spike insulin the same way carbs do. If your goal is autophagy, skip the coconut oil. If your goal is fat loss and ketosis, small amounts may be okay.

Does decaf coffee break a fast?

No. Decaf coffee has the same minimal calorie count as regular coffee and won’t break your fast. Research shows both caffeinated and decaf coffee may lower the risk of type 2 diabetes.

What if I can’t drink black coffee?

Try cold brew. It’s naturally less bitter and acidic than hot coffee because of the brewing process. You might find it more enjoyable without milk or sugar. If you still can’t stand black coffee, switch to tea or stick with water.

Will zero calorie energy drinks break my fast?

Zero calorie energy drinks often contain artificial sweeteners and high caffeine levels. While they have no calories, the sweeteners may trigger an insulin spike or increase hunger cravings. They also typically contain various additives that could interfere with fasting benefits. Plain water, coffee, or tea are better choices.

Choosing the right beverages during your fasting window can make or break your results. A key concern for many is whether fasting burns fat or muscle, and proper hydration plays a role in this. Another common question is whether butter breaks a fast, especially for those following keto protocols. If weight management is your goal, understanding whether 75 kg is overweight can help you measure your progress.