Is it okay to have coffee when fasting?

October 31, 2025 •

4 min read

According to a 2020 study, drinking black coffee during a 10-hour fast does not affect triglyceride or glucose levels, confirming that it is okay to have coffee when fasting, provided there are no added calories. However, adding ingredients like milk, sugar, or cream can disrupt the fasted state, so careful preparation is key for maximizing benefits.

Quick Summary

Black coffee is generally acceptable during a fast due to its minimal calorie content, while calorie-rich additions will break a fast. It can also enhance fat burning, improve mental clarity, and suppress appetite. Moderation and listening to your body are key.

Key Points

Black Coffee is Safe: Plain black coffee, containing fewer than 5 calories per cup, does not break a fast for most intermittent fasting protocols.
Additives Break a Fast: Adding sugar, milk, cream, or caloric sweeteners will break a fast by triggering an insulin response.
Enhances Fat Burning: The caffeine in black coffee can boost your metabolism and increase fat oxidation, potentially enhancing weight loss effects.
Suppresses Appetite: Coffee can help curb hunger and cravings, making it easier to stick to your fasting schedule.
Moderation is Key: Excessive caffeine intake can lead to negative side effects like anxiety, jitters, and sleep disruption. It's best to moderate your consumption.
Choose Plain Over Flavored: While flavored coffee beans are often okay, flavored syrups and sugary additions are not. Stick to natural spices like cinnamon for flavor.
Consult a Doctor: If you are fasting for medical tests, bloodwork, or have underlying health conditions, consult your doctor before consuming coffee.

The Core Principles of Fasting and Coffee

For those who practice fasting, particularly intermittent fasting (IF), the goal is often to abstain from calories for a set period to elicit specific metabolic responses. When the body is in a fasted state, it switches from burning glucose for energy to burning stored fat, a process known as metabolic switching. It also initiates autophagy, a cellular clean-up and repair process. The critical question for many is whether their daily coffee ritual can continue during this fasting window without sabotaging these beneficial processes. The consensus among many health experts and recent studies is that black coffee is acceptable and can even be an ally in your fasting journey.

Why Black Coffee Gets the Green Light

Plain black coffee, or decaf, contains a negligible number of calories—typically fewer than 5 calories per cup. For most fasting protocols, this amount is too minimal to trigger a significant insulin response or disrupt the metabolic state. This means your body can continue to burn fat and conduct cellular repair, making black coffee a safe beverage choice.

Coffee's Potential Benefits While Fasting

Instead of simply being a permissible beverage, black coffee can actively enhance the benefits of fasting:

Enhances Fat Burning: The caffeine in coffee acts as a stimulant, which can boost your metabolic rate and increase the process of fat oxidation. This thermogenic effect, where your body produces more heat and burns calories, can help amplify the fat-burning effects already in play during a fast.
Suppresses Appetite: Caffeine can help curb hunger and reduce cravings, which makes sticking to your fasting schedule much easier, especially during the initial adjustment period. This is partly due to caffeine's effect on hormones like ghrelin, the 'hunger hormone'.
Improves Mental Clarity and Focus: Many fasters report experiencing increased focus and mental clarity, which is further amplified by coffee's caffeine content. Caffeine blocks adenosine, a neurotransmitter that promotes sleepiness, helping you feel more alert and productive.
Supports Autophagy: Some evidence suggests that compounds in coffee, such as polyphenols, may actually enhance autophagy. This complements the cellular cleansing process that is a key benefit of fasting, aiding in cellular renewal.

What Absolutely Breaks a Fast

While black coffee is largely benign, what you add to it can completely negate your fasting efforts. It's crucial to be aware of the following additions that will break a fast:

Sugar and Syrups: Any form of sugar, honey, agave, or high-fructose corn syrup will cause an insulin spike, immediately halting the fasted state.
Milk and Cream: Dairy contains lactose (a sugar), protein, and fat. Even a small splash introduces enough calories and macronutrients to signal to your body that it's no longer fasting.
Bulletproof Coffee (Butter/MCT Oil): This popular keto beverage contains a significant number of calories from fat, which technically breaks a traditional fast. While it doesn't cause an insulin spike, it does provide fuel, preventing your body from entering a deeper fasted state and hindering processes like autophagy.
Artificial Sweeteners: Some calorie-free sweeteners may trigger an insulin response in sensitive individuals or disrupt gut health. For a 'clean fast,' it is safest to avoid them entirely.

Comparison Table: Fasting-Friendly vs. Fast-Breaking Coffee Options


Coffee Option	Fasting-Friendly?	Reason
Plain Black Coffee	Yes	Negligible calories; does not trigger insulin response.
Espresso (Black)	Yes	Concentrated black coffee; adheres to low-calorie rule.
Cold Brew (Plain)	Yes	Smoother, less acidic option; safe if unsweetened.
Decaf Coffee (Plain)	Yes	Minimal caffeine and calories; retains antioxidants.
Coffee with Sugar	No	Sugar is a carb that spikes insulin, breaking the fast.
Coffee with Milk/Cream	No	Calories and macronutrients trigger digestion.
Flavored Syrups	No	Sugar-laden syrups end the fasted state immediately.
Bulletproof Coffee	No (for strict fast)	Calories from fat (butter/MCT oil) technically break the fast.

Practical Tips for Drinking Coffee While Fasting

To get the most out of your coffee during a fast and minimize potential downsides, follow these tips:

Listen to Your Body: For some, coffee on an empty stomach can cause jitters, anxiety, or stomach irritation. If this happens, consider reducing your intake, switching to a lower-acid cold brew, or opting for decaf.
Time It Right: Drinking coffee earlier in your fasting window can help with morning hunger and focus. However, avoid consuming it too late in the day to prevent sleep disruption, which can interfere with fasting benefits.
Stay Hydrated: Coffee is a mild diuretic. Always balance your coffee intake with plenty of water to stay properly hydrated throughout your fast and avoid potential headaches or fatigue.
Know Your 'Why': The strictness of your fast can depend on your goals. For weight loss, a small amount of fat (dirty fasting) might not hinder progress, but for maximizing cellular repair (autophagy), any calories are best avoided.

A Final Word on Combining Fasting and Coffee

So, is it okay to have coffee when fasting? For most people engaging in fasting for weight management or metabolic health, the answer is a resounding yes—as long as it’s black. Black coffee can be a powerful tool for suppressing appetite, enhancing focus, and boosting fat-burning, all of which can aid your fasting goals. The key is to avoid calorie-rich additives and to pay attention to your body's individual response. As with any significant dietary change, it is always wise to consult a healthcare professional to ensure it aligns with your specific health needs.

Conclusion

In summary, black coffee is a safe and potentially beneficial addition to most fasting regimens, offering support for appetite control, metabolism, and mental focus. The potential benefits are best realized when it is consumed without caloric additives like sugar, milk, or cream, which would break the fasted state. By adhering to the 'black only' rule and moderating intake, coffee drinkers can enjoy their daily brew while maximizing the positive effects of their fast.

Sources

American Journal of Clinical Nutrition
Clinical Nutrition ESPEN
Healthline
Journal of Clinical Chemistry and Laboratory Medicine
Nutrients

Frequently Asked Questions

Yes, even a small amount of milk or cream will technically break a fast because it contains calories and macronutrients that trigger a metabolic response. The safest approach is to stick to black coffee.

Artificial sweeteners are a debated topic within fasting communities. While calorie-free, they can sometimes trigger an insulin response or increase hunger cravings. For a strict or 'clean' fast, it is best to avoid them.

Yes, plain decaf coffee is also fasting-friendly. It retains many of coffee's beneficial antioxidants and polyphenols, and won't break a fast due to its minimal caloric content. This is a good option for those sensitive to caffeine.

For most people, drinking coffee on an empty stomach is fine, and some may find it helps curb appetite. However, if you experience acid reflux, jitters, or digestive discomfort, you may be sensitive and should listen to your body.

Moderation is key. A moderate intake of 1–3 cups (8–24 oz) of black coffee per day is generally acceptable for most people while fasting. Excessive intake can lead to side effects.

Yes, caffeine has a long half-life and can disrupt sleep patterns, especially if consumed late in the day. It's best to time your coffee intake for earlier in your fasting window to avoid this.

For a strict water-only fast, black coffee would technically break the rules. However, many people who follow a modified approach include it. The decision depends on how strictly you adhere to your fasting protocol.