Nutrition Diet: What to drink during intermittent fasting 20/4? Expert guide

October 16, 2025 •

5 min read

According to Johns Hopkins neuroscientist Mark Mattson, the body shifts to burning fat after hours without food, a process known as metabolic switching. During the intense 20/4 fasting schedule, knowing what to drink during intermittent fasting 20/4 is crucial for maintaining this metabolic state, staying hydrated, and managing hunger.

Quick Summary

This guide outlines the essential calorie-free beverages suitable for the 20/4 fasting window, including water, black coffee, and unsweetened teas. It emphasizes the critical role of maintaining proper hydration and mineral balance with electrolytes to support energy levels and reduce side effects during prolonged fasting.

Key Points

Stay Hydrated: Drink plenty of zero-calorie fluids, primarily water, throughout the 20-hour fasting window to prevent dehydration and fatigue.
Black is Best: Stick to plain, black coffee and unsweetened teas to avoid adding calories and breaking your fast.
Replenish Electrolytes: Supplementing with zero-calorie electrolytes is crucial, especially during a longer 20/4 fast, to avoid dizziness, headaches, and muscle cramps.
Know Your 'No's': Avoid all calorie-containing drinks, including sugar, milk, and specialty coffees, as they will break your fast.
Time It Wisely: Use caffeinated beverages like black coffee strategically early in your fast to suppress appetite and boost focus.
Experiment Safely: While some allow small amounts of fats or sweeteners, a strict fast for autophagy is best kept clean with zero-calorie options only.
Listen to Your Body: Pay attention to signs of electrolyte imbalance, like headaches or muscle cramps, and adjust your intake as needed.

The Core Principle: Zero Calories

Intermittent fasting (IF) works by restricting caloric intake to a specific window, allowing your body to enter a fasted state where it burns stored fat for energy. For the 20/4 method, where you fast for 20 hours and eat during a 4-hour window, the rules for your non-eating period are straightforward: only consume beverages that contain zero calories. Any significant caloric intake will signal your body to switch from a fat-burning, fasted state back into a fed state, halting the metabolic benefits you are trying to achieve. This strict adherence is particularly important during a longer fasting period like 20 hours to maximize effectiveness. While some 'dirty fasting' proponents suggest small allowances, a 'clean' fast focused purely on non-caloric fluids is the most reliable way to ensure you stay in a true fasting state.

The Importance of Hydration During 20/4 Fasting

Proper hydration is not just about staving off thirst; it is a critical component of a successful 20/4 fast. When you stop eating, your body naturally excretes more water and electrolytes due to lower insulin levels. This can lead to dehydration, which manifests as headaches, dizziness, fatigue, and other unpleasant side effects. Staying well-hydrated throughout your 20-hour fast is essential for regulating body temperature, supporting brain function, and maintaining proper energy levels. Many people mistake thirst for hunger, and drinking a glass of water can often satisfy what feels like a craving for food. To optimize your experience, consider sipping water regularly throughout the day rather than waiting until you feel thirsty.

Your Go-To Fasting Beverages

During your 20-hour fasting window, you have a variety of delicious and satisfying drink options that won't break your fast. Choosing high-quality ingredients can elevate your experience and make sticking to the plan much easier.

Water and Sparkling Water: This is your foundation. Plain water is calorie-free and essential for hydration. Sparkling water can provide a fizzy alternative that feels more substantial and can help curb cravings.
Black Coffee: With only 3-5 calories per cup, black coffee is a popular fasting drink. The caffeine can help suppress appetite, increase energy levels, and enhance fat burning, making the fasting window more manageable. For those sensitive to caffeine, decaf coffee is also a great option. To avoid breaking your fast, skip the sugar, milk, and cream.
Unsweetened Tea: Teas of all kinds—green, black, white, and herbal—are excellent choices, provided they are unsweetened and contain no milk or cream. Green tea, in particular, is rich in antioxidants and catechins that can aid metabolism and hunger control. Herbal teas like ginger or chamomile can be soothing and offer digestive benefits.
Lemon Water: A small squeeze of fresh lemon into your water adds flavor with minimal calories. However, large amounts of lemon juice contain more calories and sugar, so moderation is key to avoid breaking your fast.

The Critical Role of Electrolytes

For a longer fast like 20/4, electrolyte replenishment becomes critical. Electrolytes are essential minerals—primarily sodium, potassium, and magnesium—that regulate nerve and muscle function, hydrate the body, and balance blood acidity. The initial phase of fasting can deplete these minerals quickly. Adding zero-calorie electrolyte supplements or a pinch of high-quality salt to your water can prevent common symptoms like headaches, fatigue, and muscle cramps. Look for clean products that are free of sugar, artificial sweeteners, and fillers to ensure you don't inadvertently break your fast.

What Definitely Breaks Your Fast

To maintain a true fasted state and reap the full benefits of your 20/4 schedule, it is vital to avoid certain beverages. These drinks contain calories that will trigger an insulin response and metabolic switch.

Sugary drinks: This includes regular soda, juices, and sweetened teas.
Dairy and milk alternatives: Adding milk, cream, or plant-based milks (like almond or oat) to coffee or tea introduces calories that break a fast.
Caloric coffee additives: Syrups, honey, and other flavorings must be avoided.
Bulletproof coffee: While popular in ketogenic circles, adding butter or MCT oil to coffee adds significant calories and breaks a standard fast.
Alcohol: All forms of alcohol contain calories and must be avoided during your fast.
Bone broth: This contains protein and calories, and while it's nutritious, it should be consumed during your eating window.

Fasting-Friendly Drinks vs. Fast-Breaking Drinks

To make it easy to remember what to drink, use the following comparison table. It highlights the primary fasting goal for each type of beverage.


Drink Category	Fasting-Friendly Options	Fast-Breaking Options	Why?
Water	Plain, sparkling, or with a splash of fresh lemon juice.	Flavored waters with added sugar or sweeteners.	Calorie-free and essential for hydration. Added sugar breaks a fast.
Coffee	Plain black or decaf.	With milk, cream, sugar, or Bulletproof additions.	Negligible calories. Additives trigger an insulin response.
Tea	Unsweetened green, black, white, or herbal teas.	Sweetened teas, milky tea lattes, or teas with honey.	Contains beneficial antioxidants. Added sugars or milk contain calories.
Electrolytes	Zero-calorie electrolyte powders or salts.	Sports drinks with sugar or electrolyte products with sweeteners and fillers.	Replenishes lost minerals without calories. Sugary drinks break the fast.
Other	Diet sodas (debated, but technically calorie-free).	Fruit juices, smoothies, alcohol.	Zero-calorie alternatives. High-calorie drinks trigger metabolic processes.

Strategic Timing for Your Fasting Drinks

While you can consume fasting-friendly beverages at any point during your 20-hour window, strategic timing can help you maximize benefits and overcome challenges. Many people find it helpful to start their day with a glass of water to rehydrate. A cup of black coffee or green tea can be a lifesaver in the morning, as the caffeine can suppress appetite and enhance mental alertness during the hardest early hours. Consider saving herbal teas for later in the day when you might want a warm, comforting beverage to calm you down and distract from hunger. Replenishing electrolytes, either by sipping salt water or a zero-calorie supplement, is a good habit throughout the fast, especially if you exercise or live in a hot climate.

Conclusion: Hydration Is Key to Your 20/4 Success

Navigating the 20/4 intermittent fasting schedule requires discipline and a clear understanding of which beverages support your goals. Beyond the obvious avoidance of caloric drinks, staying properly hydrated with water and supplementing with electrolytes are fundamental to a positive and sustainable experience. Calorie-free options like black coffee and unsweetened teas can help manage hunger and provide an energy boost, making your 20-hour fast feel more effortless. Always listen to your body and choose the cleanest, most natural beverage options to ensure you're maintaining a true fasted state and optimizing the metabolic benefits of your fasting regimen. Consulting a healthcare professional before starting any new diet is always recommended, especially with a longer fasting schedule.

Expert advice from Johns Hopkins neuroscientist Mark Mattson on intermittent fasting:(https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work)

Frequently Asked Questions

A small amount of fresh lemon juice in water is generally acceptable during a fast, as it contains minimal calories. However, a large amount of lemon juice could have enough calories to break a strict fast, so it is best to use it sparingly.

Technically, diet soda contains zero calories and will not break a fast in terms of caloric intake. However, the artificial sweeteners can trigger cravings or an insulin response in some individuals, so opinions are mixed and it depends on your fasting goals.

No, bone broth contains protein and calories and will break a fast. It is a nutritious beverage but should be consumed only during your 4-hour eating window.

Drinking black coffee early in your fast, such as in the morning, can help suppress appetite and boost mental clarity. Many people find this helps them power through the fasting window until their first meal.

For a longer fast like 20 hours, electrolyte supplementation is highly recommended. Fasting can deplete essential minerals, and replenishing them with a zero-calorie supplement can prevent side effects like headaches and fatigue.

If you find black coffee too bitter, try drinking unsweetened teas, such as green, herbal, or white tea. Cold-brew coffee, which has lower acidity, is another good option that can be more palatable without milk or sugar.

If the flavored water contains zero calories and is free of any added sugars or sweeteners, it should be fine. Always double-check the nutrition label to ensure it won't break your fast.