During a 24-hour fast, you can drink water, black coffee, plain tea, and a few other zero-calorie beverages without disrupting the metabolic benefits you’re fasting for. The key rule is simple: anything with calories, protein, or sugar will shift your body out of its fasted state to some degree. But the details matter, because some drinks sit in a gray zone depending on your fasting goals.
Water Is Your Foundation
Plain water, still or sparkling, contains no calories and keeps you hydrated throughout the fast. This sounds obvious, but most people underestimate how much they need. When you’re not eating, you lose a significant source of daily water intake (food accounts for roughly 20% of your hydration), so you’ll want to drink more than usual. Aim for at least 8 to 10 cups spread across the day. Mineral water or sparkling water with no added flavors works just as well and can help settle your stomach when hunger pangs hit.
Black Coffee and Plain Tea
Black coffee and unsweetened tea are safe during a 24-hour fast. Coffee contains essentially zero calories when consumed without milk, cream, or sugar, and clinical data shows it does not significantly affect fasting blood glucose levels. Tea, whether green, black, white, or herbal, follows the same rule: plain and unsweetened.
Caffeine can actually work in your favor during a fast. It blunts appetite and provides an energy boost when your body is adjusting to no food intake. That said, caffeine on an empty stomach can cause jitteriness or acid reflux for some people, so pay attention to how you feel and consider switching to herbal tea in the afternoon.
The moment you add milk, cream, or sugar to your coffee or tea, you introduce calories and trigger an insulin response. Even a small splash of milk contains enough protein and lactose to technically break the fast. If you need something to cut the bitterness of black coffee, a zero-calorie sweetener is a better option (more on that below).
Stevia, Monk Fruit, and Other Zero-Calorie Sweeteners
If plain water and black coffee feel too austere for 24 hours, natural zero-calorie sweeteners can make your drinks more tolerable without spiking blood sugar or insulin. Stevia and monk fruit are the two best-studied options. Clinical research shows monk fruit extract has no impact on blood sugar levels, while sucrose causes a 70% spike shortly after ingestion. Stevia performs similarly: studies in both healthy individuals and people with diabetes show it does not raise blood glucose, insulin, or lipid levels.
Adding a few drops of liquid stevia to sparkling water or monk fruit sweetener to your tea gives you a hint of sweetness at zero metabolic cost. Sugar alcohols like erythritol also appear to have minimal effect on blood sugar, though some people experience digestive discomfort from them, which you definitely don’t want on an empty stomach.
Apple Cider Vinegar in Water
Mixing 1 to 2 teaspoons of apple cider vinegar into a glass of water is a popular fasting drink, and there’s reasonable science behind it. Apple cider vinegar contains negligible calories (about 3 per tablespoon) and may help curb cravings during a fast. The acetic acid in vinegar appears to lower the glycemic impact of foods and may suppress certain fat-storage pathways in the liver. Some fasters report it takes the edge off hunger, possibly by slowing gastric emptying.
Always dilute it well. Drinking apple cider vinegar straight can erode tooth enamel and irritate your throat.
Electrolytes and Salt Water
One of the most overlooked drinks during a 24-hour fast is plain water with a pinch of salt. When you stop eating, your body sheds sodium and other electrolytes more quickly, which can cause headaches, dizziness, fatigue, and muscle cramps. A quarter teaspoon of sea salt or Himalayan salt dissolved in water a few times throughout the day can prevent this without adding calories.
You can also use electrolyte powders or tablets, but check the label. Many contain sugar, maltodextrin, or other ingredients that will break your fast. Look for products that list only sodium, potassium, and magnesium with zero calories and no sweeteners beyond stevia or monk fruit.
Drinks That Technically Break Your Fast
Some beverages contain calories and nutrients but are still commonly consumed during longer fasts because they keep the body in a fat-burning state. Whether these work for you depends on why you’re fasting.
Bone broth is the most common example. A cup contains roughly 30 to 50 calories and a small amount of protein (about 2 grams per serving based on average amino acid content). Those calories and amino acids will technically end your fasted state. Amino acids, particularly leucine, activate a cellular pathway that directly shuts down autophagy, the cellular cleanup process many people fast to trigger. If your goal is autophagy or a strict metabolic fast, skip the bone broth. If you’re fasting primarily for calorie restriction or digestive rest, a cup of bone broth can help replenish electrolytes and make the 24 hours far more manageable.
Coffee with a tablespoon of butter, coconut oil, or MCT oil falls into the same category. The fat provides calories (around 100 to 120 per tablespoon) and will break a strict fast, but because fat alone produces a minimal insulin response, it won’t knock you out of ketosis. This is a compromise drink: useful if you’re struggling to complete the fast, but not compatible with a true zero-calorie approach.
What to Avoid Entirely
- Juice, soda, and sweetened drinks: Even “natural” fruit juice is concentrated sugar that will spike insulin immediately.
- Diet soda: While technically zero-calorie, some artificial sweeteners like aspartame and sucralose may provoke an insulin response in certain individuals. If you want a carbonated option, stick with plain sparkling water.
- Milk and plant milks: All contain calories from protein, fat, or carbohydrates. Even unsweetened almond milk has enough to break a fast.
- Alcohol: Drinking on a completely empty stomach accelerates absorption dramatically, stresses the liver, and dehydrates you further.
- Protein shakes or collagen drinks: Protein is the most potent trigger of the cellular pathway that stops autophagy. Even a small serving defeats the purpose of fasting.
How to Break a 24-Hour Fast
What you drink (and eat) when the fast ends matters more than most people realize. After 24 hours without food, your digestive system has slowed down considerably. Jumping straight into a large meal can cause bloating, nausea, and stomach cramps.
Start with something easy to digest about 15 to 30 minutes before your first real meal. A small cup of bone broth, a glass of water with a pinch of salt, or a light smoothie works well. Then move into a modest, balanced meal rather than a feast. Foods high in fiber, lean protein, and healthy fats are easier on your system than processed or greasy food. Most people find their digestion normalizes within a meal or two after a 24-hour fast, so there’s no need for an elaborate multi-day refeeding process. That kind of protocol is reserved for fasts lasting many days or weeks.
A Simple Drinking Schedule
Spreading your beverages throughout the day makes a 24-hour fast significantly easier. A practical approach: start the morning with a glass of water and a pinch of salt. Mid-morning, have black coffee or tea. Early afternoon, try sparkling water with a squeeze of lemon or a few drops of stevia. Late afternoon, another cup of tea or salted water. Evening, herbal tea like peppermint or chamomile, which can calm your stomach and signal your body to wind down. This pattern keeps something in your hands and your stomach at regular intervals, which makes the psychological challenge of fasting much more manageable than white-knuckling it with nothing but tap water.