What can you drink during fasting? A comprehensive guide

October 19, 2025 •

4 min read

Approximately 75% of Americans are chronically dehydrated, a state which fasting can exacerbate if not managed correctly. Understanding what can you drink during fasting? is critical for maintaining hydration, energy, and maximizing health benefits. This guide outlines the best beverage choices to support your fasting goals.

Quick Summary

Clear beverages like plain water, black coffee, and herbal tea are generally acceptable, while high-calorie drinks such as soda and juice will break a fast. Electrolyte intake is also important, especially for longer fasts, to maintain balance and avoid side effects.

Key Points

Prioritize Zero-Calorie Fluids: The safest and most effective strategy for a clean fast is to consume only plain water, black coffee, or unsweetened tea to avoid triggering an insulin response.
Replenish Electrolytes for Longer Fasts: For extended fasting periods, adding a pinch of salt to your water or using a zero-calorie electrolyte mix is essential to prevent mineral depletion and manage potential side effects like headaches and fatigue.
Avoid Sugars and Artificial Sweeteners: High-calorie sweeteners and even zero-calorie artificial ones should be avoided as they can cause insulin spikes or confuse the body, potentially undermining fasting benefits.
Distinguish Between Fasting Protocols: Understand the difference between 'clean' (zero calories) and 'dirty' fasting (minimal calories). Choose the approach that aligns with your health goals and personal tolerance.
Listen to Your Body: Pay close attention to signs of dehydration, dizziness, or digestive discomfort. Drink fluids regularly, especially water, and adjust your fasting plan as needed.

The Core Principle: The Calorie Rule

The fundamental principle of fasting, particularly for its metabolic benefits like improved insulin sensitivity and autophagy, is to avoid consuming calories. Any significant calorie intake, especially from sugar or protein, triggers a digestive and insulin response that pulls the body out of a fasted state. A strict or 'clean' fast requires zero calories, while some approaches, known as 'dirty fasting,' allow a minimal calorie intake, often under 50-100 calories. For most people, sticking to truly zero-calorie options is the safest way to ensure fasting benefits are not compromised.

The Green Light: Fasting-Friendly Beverages

Staying hydrated is paramount during a fast. Since much of our daily fluid intake comes from food, it’s vital to be intentional about drinking enough fluids during fasting windows. The following beverages are generally considered safe for most fasting protocols:

Plain Water: The absolute best option. Plain or sparkling water provides hydration without calories. You can enhance the flavor by infusing it with fresh lime or lemon slices, as the calorie count is negligible.
Black Coffee: Unsweetened, black coffee is a popular choice for many fasters. It contains only 3-5 calories per cup and can help suppress appetite and boost metabolism. The caffeine provides a natural energy lift. However, avoid adding sugar, milk, cream, or caloric sweeteners.
Plain Tea: Green tea, black tea, and most herbal teas are excellent choices, provided they are unsweetened. They offer antioxidants and hydration without breaking a fast. Herbal teas like chamomile or ginger can also aid digestion and relaxation.
Electrolyte Water: For prolonged fasts or during hot weather, replenishing electrolytes (minerals like sodium, potassium, and magnesium) is crucial to prevent dizziness, headaches, and fatigue. Consider adding a pinch of pink salt to your water or using a sugar-free electrolyte mix.
Apple Cider Vinegar (ACV): Diluted ACV can be consumed during a fast. Mixing 1–2 teaspoons into a glass of water may help with hydration and curb cravings for some individuals.

Proceed with Caution: The Grey Area of 'Dirty Fasting'

'Dirty fasting' is a less restrictive form of intermittent fasting that allows a small number of calories during the fasting window. While this approach may make fasting more manageable for some, it's important to understand the trade-offs. The potential benefit of easier adherence must be weighed against the risk of disrupting the metabolic processes that a clean fast aims to achieve, such as autophagy.

Bone Broth: Rich in nutrients and electrolytes, bone broth can be a valuable supplement during longer fasts to replenish minerals. However, it contains calories and protein, so it will technically break a strict fast. It is best reserved for dirty fasting protocols.
Bulletproof Coffee: This involves adding butter and/or MCT oil to coffee. While popular in ketogenic circles, the added fats contain calories, meaning it breaks a clean fast. It supports ketosis but restricts autophagy.
Diet Soda: The effect of diet soda on fasting is a subject of debate. While calorie-free, the artificial sweeteners can trigger a cephalic phase insulin response in some people, confusing the body and potentially slowing down fat burning. For those prioritizing autophagy and metabolic benefits, plain beverages are the safer choice.

The Red Zone: Beverages to Strictly Avoid

For any fasting approach, certain beverages should be avoided completely during fasting windows as they will quickly break the fast and reverse its intended effects.

Sugary Drinks: This includes regular soda, fruit juices, and any sweetened drinks. They are loaded with calories and sugar, causing a rapid insulin spike.
Alcohol: Alcoholic beverages contain calories and interfere with fasting and other metabolic processes.
Dairy Products: Milk, cream, and other dairy products contain calories and sugars (lactose), which will break a fast.
Sweetened Teas and Coffees: Adding honey, sugar, syrup, or caloric creamers to your tea or coffee completely nullifies the fasting state.

Beverage Comparison for Fasting


Beverage	Fasting-Safe?	Considerations
Plain/Sparkling Water	Yes	Ideal for hydration, calorie-free.
Black Coffee	Yes	Unsweetened, no additives. Aids appetite control and metabolism.
Herbal Tea (Plain)	Yes	Unsweetened, no additives. Good for hydration and antioxidants.
Electrolyte Water	Yes	Use sugar-free powder or pinch of salt for longer fasts to replenish minerals.
Apple Cider Vinegar	Yes (Diluted)	Mix a small amount with water; can help with cravings.
Bone Broth	No (Strict Fast) / Yes (Dirty Fast)	Contains calories, use cautiously. Breaks a strict fast but provides nutrients in a modified fast.
Diet Soda	Debatable	Zero calories but artificial sweeteners may trigger insulin response and cravings.
Bulletproof Coffee	No (Clean Fast)	Contains calories from fat. Breaks a clean fast but acceptable for fat-based dirty fasts.
Sugary Drinks/Juice	No	High in calories and sugar; causes insulin spike.
Dairy/Cream	No	Contains calories and sugar; breaks a fast.

The Risks of Dehydration While Fasting

Dehydration is a significant risk during fasting, especially as you lose fluids that would normally be replenished by food. Symptoms can range from mild fatigue and headaches to more serious issues like kidney strain and irregular heartbeats. To mitigate these risks, it is important to sip fluids regularly throughout your fasting window and not wait until you are extremely thirsty.

Conclusion

Deciding what can you drink during fasting depends on your specific goals and chosen protocol. For a classic, 'clean' fast aimed at achieving maximum metabolic benefits like autophagy and improved insulin sensitivity, the safest and most effective choices are plain water, black coffee, and unsweetened teas. These zero-calorie options ensure the body remains in a fully fasted state while supporting hydration. For those following a less strict approach, such as dirty fasting, some low-calorie options like bone broth can be included, but should be done with awareness that the fast is technically broken. Always prioritize hydration and listen to your body, consulting a healthcare professional if you have any underlying health conditions before starting a fasting regimen.

An excellent source for further reading on fasting and metabolic health can be found via Johns Hopkins Medicine, which explores the science and various fasting methods.

Frequently Asked Questions

Yes, a small amount of fresh lemon or lime juice in your water is generally acceptable during fasting. The calorie count is very low and will not disrupt your fast significantly.

This is a point of debate. While diet sodas contain no calories, the artificial sweeteners can trigger a cephalic phase insulin response in some individuals. For a strict fast, it is best to avoid them, but for a dirty fast, the effect may be negligible.

Bone broth contains calories and protein, so it will technically break a clean fast. It is typically used in 'dirty fasting' or during modified fasts to replenish electrolytes and nutrients. For a zero-calorie fast, it should be avoided.

Staying adequately hydrated is key. A good guideline is to aim for at least 8-10 glasses of water per day, and to sip it consistently throughout your fasting window.

Yes, plain, unsweetened herbal teas like chamomile or ginger tea are safe and can offer additional benefits. Just be sure not to add any honey, sugar, or milk.

Dirty fasting is a less strict form of intermittent fasting where you consume a small number of calories (typically under 50-100) during your fasting window. This is unlike 'clean' fasting, which involves consuming zero calories.

Electrolytes are crucial, especially during longer fasts, to maintain proper fluid balance. Plain water or a sugar-free electrolyte supplement can prevent symptoms like headaches and muscle cramps.