Can You Drink Coffee on a 14-Hour Fast?

December 15, 2025 •

4 min read

Research indicates that black coffee contains a negligible number of calories—typically between 2 and 5 per cup—which is generally not enough to break a fast. So, can you drink coffee on a 14-hour fast? The short answer is yes, but it hinges entirely on what, if anything, you add to it.

Quick Summary

Plain black coffee is permissible during a 14-hour fast as it contains minimal calories that do not disrupt key metabolic processes like fat-burning or autophagy. Avoid caloric additives.

Key Points

Black Coffee is Fasting-Friendly: Plain black coffee, containing minimal calories, will not break a 14-hour fast, allowing your body to continue burning fat.
Avoid All Caloric Additives: Milk, sugar, cream, and high-calorie sweeteners introduce energy that stops the fasting process and should be avoided during your fasting window.
Boost Fasting Benefits: The caffeine in black coffee can enhance fat-burning, suppress appetite, and improve mental focus, complementing your fasting goals.
Decaf is a Safe Alternative: Decaffeinated coffee is also safe for fasting and is a great option for those who are sensitive to caffeine or want a later-day beverage.
Listen to Your Body: If you experience stomach upset, consider reducing your intake, switching to a low-acid coffee like cold brew, or increasing your water intake to stay hydrated.
Autophagy Focus Requires Purity: For those fasting specifically to maximize autophagy (cellular repair), it is best to stick to strictly black coffee, as any caloric input, even from a 'dirty fast', could potentially interfere.

Understanding How Fasting Works

Intermittent fasting, such as the 14-hour protocol, involves alternating periods of eating and fasting to encourage metabolic switching. This is the process where your body exhausts its sugar stores and begins burning fat for fuel. To ensure your body stays in this fat-burning state and continues other beneficial processes like autophagy (cellular repair), it is crucial to consume only non-caloric beverages during the fasting window. This is why the composition of your coffee is so important.

The Verdict on Black Coffee and Your Fast

Plain, black coffee is the safest and most recommended option for a 14-hour fast. Since it contains a minimal number of calories (almost zero), it does not trigger an insulin response or provide significant energy for your body to metabolize. This allows your body to remain in a fasted state, continuing to burn fat and conduct cellular repair effectively. You can enjoy it hot, iced, as an espresso, or cold brew without worry.

The Rules of Fasting Coffee: Additives that Break the Fast

While black coffee is permissible, many popular coffee additives will immediately break your fast by providing calories, sugars, or fats that trigger a metabolic response.

Additives to Avoid

Sugar and Syrups: Any form of sugar, including honey, maple syrup, or flavored syrups, will cause a spike in blood sugar and insulin, halting the fat-burning process. These are pure carbohydrates that provide energy, breaking the fast immediately.
Milk and Cream: Adding dairy or even plant-based milks introduces calories, carbohydrates, and proteins into your system. Even a small splash contains lactose (a form of sugar) and fat, triggering an insulin response. This includes whole milk, skim milk, oat milk, and almond milk.
Bulletproof Coffee: This popular keto addition, which contains butter and MCT oil, provides significant calories and fat. Although it is low in carbohydrates and won’t spike insulin dramatically, it introduces fuel that pulls your body out of a true fasted state, limiting benefits like autophagy.
Collagen and Protein Powder: Any supplement containing protein or significant calories will break a fast. Your body will shift its focus from cellular repair to digestion.

The Controversial Case of Zero-Calorie Sweeteners

The use of zero-calorie sweeteners like stevia, monk fruit, and erythritol during a fast is debated. While they do not contain calories, the sweet taste can trigger an anticipatory insulin response in some individuals. For a strict or “clean” fast focused on maximizing metabolic benefits like autophagy, it is best to avoid them. For those with weight loss as the primary goal, a small amount may be acceptable if it doesn't cause cravings.

Benefits of Black Coffee During Your Fast

Drinking black coffee can actually complement your 14-hour fasting routine and enhance some of its effects.

Appetite Suppression: The caffeine in coffee can help reduce hunger and cravings, making it easier to stick to your fasting window. This is a major advantage for those new to fasting or struggling with morning hunger pangs.
Enhanced Fat Burning: Caffeine is known to boost metabolism and increase fat oxidation by stimulating thermogenesis. This means your body can burn more stored fat for energy while in a fasted state, supporting weight loss.
Improved Mental Focus: Caffeine acts as a central nervous system stimulant, improving alertness, concentration, and overall cognitive performance. For those who experience fatigue during fasting, coffee can provide a welcome energy boost.
Increased Autophagy: Some studies suggest that coffee’s polyphenols can help induce autophagy, the cellular cleanup process that promotes longevity and repair. This enhances one of the key health benefits of fasting. Notably, this effect has been observed with both caffeinated and decaffeinated coffee.

Comparison of Coffee and Additives for Fasting


Item	Calories/Macronutrients	Insulin Response?	Breaks Fast?	Best For...
Black Coffee	~3-5 calories, no sugar/fat	No	No	Maximizing all fasting benefits
Decaf Coffee	~3-5 calories, no sugar/fat	No	No	Caffeine-sensitive individuals, late-day boost
Coffee with Milk	Caloric (carbs, fat, protein)	Yes	Yes	Eating window only
Coffee with Sugar	Caloric (carbs)	Yes	Yes	Eating window only
Bulletproof Coffee	Caloric (fat)	Minimal/No	Yes*	Keto-based fat fasting (limits autophagy)
Zero-Calorie Sweetener	Negligible	Varies by individual	Debated	Moderation for weight loss, avoid for strict fast

*Note: Breaks a strict fast focused on autophagy, but acceptable for some variations like 'dirty fasting.'

Handling Potential Downsides

For some, drinking coffee on an empty stomach can lead to digestive discomfort such as acid reflux, heartburn, or nausea. To mitigate this, consider a few strategies:

Reduce Intake: Try drinking a smaller amount of coffee initially and see how your body reacts. Many find that one cup is sufficient without causing issues.
Choose Low-Acid Coffee: Opt for specialty low-acid or cold brew coffee, as the latter brewing method naturally reduces acidity and can be gentler on the stomach.
Ensure Hydration: Coffee has diuretic properties, so it's important to drink plenty of water alongside it to prevent dehydration. A good practice is to have a full glass of water before and after your coffee.

Conclusion

Yes, you can confidently drink coffee on a 14-hour fast, provided you stick to the golden rule: keep it black. The minimal calories in black coffee will not disrupt your fasted state, allowing you to reap the benefits of appetite suppression, improved focus, and enhanced fat burning. While additives like milk, sugar, and caloric creamers are off-limits during your fasting window, unsweetened decaf coffee is a safe and beneficial alternative for those who are caffeine-sensitive. Always listen to your body and adjust your intake if you experience any adverse effects. For a purer fast, particularly one focused on maximizing autophagy, it is best to avoid any additives, including zero-calorie sweeteners, to prevent potential metabolic interference. Learn more about intermittent fasting at Johns Hopkins Medicine.

Frequently Asked Questions

Yes, adding any type of milk or cream, including dairy and plant-based milks, will break a fast. Milk contains calories, carbohydrates, and protein that will trigger an insulin response, ending your fasted state.

The consensus on zero-calorie sweeteners is mixed. While they don't contain calories, the sweet taste can trigger an insulin response in some people. For a strict fast aiming for full metabolic benefits like autophagy, it's best to avoid them. For weight loss-focused fasting, it may be acceptable in moderation.

If you find black coffee unpalatable or too harsh on an empty stomach, unsweetened decaf coffee, plain green tea, or herbal tea are excellent zero-calorie alternatives that won't break your fast.

Most experts recommend limiting your coffee intake to 3-4 cups (up to 400 mg of caffeine) per day. Excessive amounts of caffeine can cause jitters, anxiety, and sleep disruption, which can interfere with your fasting experience.

Yes, decaf coffee also contains beneficial compounds like polyphenols, which have been shown to induce autophagy and provide antioxidant effects. This means you can still reap some of the cellular benefits without the caffeine.

Yes, Bulletproof coffee, which contains butter and MCT oil, provides a significant number of calories. While it's popular in the keto community for providing fat-based energy, it definitively breaks a traditional fast aimed at maximizing cellular repair and fat burning from stored reserves.

Many people prefer drinking coffee in the morning or early fasting window to boost alertness and suppress appetite. Avoid drinking it too late in your fast, as it can disrupt sleep and negatively affect your overall health goals.