Can I Drink 0 Calorie Red Bull During a Fast?

October 28, 2025 •

4 min read

While intermittent fasting has surged in popularity, allowing zero-calorie drinks like water and black coffee, the rules for artificially sweetened beverages are debated. The question, 'Can I drink 0 calorie Red Bull during a fast?', delves into this gray area, considering its ingredients and their potential impact on your fasting state.

Quick Summary

The impact of consuming 0 calorie Red Bull during a fast is complex and depends on your specific fasting goals. Artificial sweeteners can sometimes trigger an insulin response or cravings, while caffeine can have varied effects. For strict fasts, it is best to avoid it, whereas those focused purely on a calorie deficit might consider it.

Key Points

Fasting Goals Matter: The permissibility of 0 calorie Red Bull depends on whether you're fasting for metabolic health/weight loss, autophagy, or gut rest.
Artificial Sweeteners Pose a Risk: Ingredients like sucralose and acesulfame potassium may trigger an insulin response in some individuals, potentially disrupting the fasted state, though data is mixed.
Caffeine is Generally Fine: Caffeine in black coffee is fasting-safe and can boost metabolism, but its effect in an energy drink with other additives should be considered.
Strict Fasting Should Avoid It: For a "clean" fast aimed at autophagy or gut rest, even zero-calorie drinks with artificial sweeteners and additives are best avoided entirely.
Alternative Options Exist: For those seeking flavor, safe alternatives like unsweetened herbal tea or sparkling water pose no risk to a fast.
Individual Response is Key: Your body's reaction to artificial sweeteners and caffeine on an empty stomach is the most important factor to consider.

Understanding the Goals of Your Fast

Before determining whether a 0 calorie Red Bull is acceptable, you must define your fasting objective. Not all fasts are created equal, and what breaks one fast might not affect another. The three primary goals people aim for are metabolic health and weight loss, autophagy (cellular repair), and gut rest. The answer to "Can I drink 0 calorie Red Bull during a fast?" varies significantly depending on which of these benefits you prioritize.

Metabolic Health and Weight Loss

For those primarily using intermittent fasting to improve metabolic health and lose weight, the main goal is to keep insulin levels low. When your body is in a fasted state, it switches from burning sugar for energy to burning stored fat. The concern with diet drinks is that artificial sweeteners, even without calories, might trigger a cephalic-phase insulin response. This is when your body, anticipating sugar from the sweet taste, releases insulin, potentially hindering your fat-burning efforts.

Autophagy and Gut Rest

If your goal is to maximize cellular repair through autophagy or to give your digestive system a complete rest, the rules are much stricter. Autophagy is a process where the body cleans out old, damaged cells. It is a sensitive process that can be halted by any intake of calories or nutrients. A strict "clean" fast for autophagy generally permits only water. Similarly, for gut rest, any additive, even non-caloric ones, can activate the digestive system and break the fast.

The Ingredients of 0 Calorie Red Bull

To evaluate the drink's impact, it's essential to look at its components beyond the "zero calories" label. Zero-sugar energy drinks typically contain several key ingredients:

Artificial Sweeteners: 0 calorie Red Bull and similar products often contain sucralose and acesulfame potassium. The effect of these on insulin levels is debated, with some studies suggesting they might trigger a response in some individuals, while older studies have shown no effect on blood glucose or insulin. The individual variability makes this a risk for a "clean" fast.
Caffeine: A key component of any energy drink, caffeine is a stimulant that can help with mental alertness and energy. When consumed without calories, like in black coffee, caffeine does not break a fast and may even enhance metabolism. However, consuming it on an empty stomach can sometimes cause jitteriness or an upset stomach, depending on individual tolerance.
Other Additives: Red Bull contains other ingredients like taurine, B vitamins, and flavorings. While these are unlikely to have a caloric impact, their effect on metabolic or gut-rest-related goals can vary and are often scrutinized in strict fasting circles.

The Verdict on 0 Calorie Red Bull and Fasting

For those seeking the strictest version of fasting, especially for autophagy or gut rest, it is best to avoid 0 calorie Red Bull. The potential for artificial sweeteners to stimulate an insulin response or digestive activity makes it a risky choice that could compromise your goals. For metabolic health and weight loss, the answer is more nuanced:

Risk vs. Reward: If a zero-calorie energy drink helps you stick to your fasting window by providing a mental boost and flavor, the minimal potential for a compromised fast might be an acceptable trade-off for you.
Individual Sensitivity: Your body's response to artificial sweeteners is a key factor. Some people can consume them without any issues, while others experience cravings or feel it affects their hunger signals.

Alternative Fasting-Friendly Beverages

If you decide that 0 calorie Red Bull is not worth the risk, plenty of other options can help you stay hydrated and energized during your fasting window. Sticking to truly non-caloric and non-stimulating drinks is the safest bet for all fasting goals.


Beverage	Fasting Compatibility	Reason
Water	Perfect	No calories, no insulin response, essential for hydration.
Black Coffee	High (for most)	Minimal calories, boosts metabolism, and suppresses appetite.
Unsweetened Green/Herbal Tea	High	Minimal calories, antioxidants, and soothing properties.
Sparkling Water (Unflavored)	Perfect	Offers carbonation for those who miss soda, no calories or sweeteners.
0 Calorie Red Bull	Low (for strict fasts), Moderate (for casual fasts)	Artificial sweeteners may trigger insulin or cravings, though calorie-free.
Diet Soda (e.g., Coke Zero)	Low (for strict fasts), Moderate (for casual fasts)	Similar to 0 calorie Red Bull, uses artificial sweeteners that are controversial.

Conclusion: The Final Word

Ultimately, whether you can I drink 0 calorie Red Bull during a fast? depends on your personal fasting goals and metabolic individuality. For the purest fast aimed at achieving maximum cellular repair and gut rest, the answer is a clear no, and it's best to stick to water, black coffee, and unsweetened tea. For those focusing on weight loss through calorie restriction, it is a more personal choice that balances the mental boost and flavor with the potential (and debated) impact of artificial sweeteners on insulin and cravings. If you choose to consume it, be mindful of how your body responds. Listening to your body is the most reliable guide, and when in doubt, a glass of water is always the safest option.

Frequently Asked Questions

There is conflicting scientific data on whether artificial sweeteners like sucralose and acesulfame potassium, found in 0 calorie Red Bull, raise insulin levels. Some studies suggest a potential increase, while others show no effect. The response is highly individual.

Yes, black coffee, which is essentially zero calories, is generally considered acceptable during a fast and can boost metabolism. However, in energy drinks, caffeine is combined with other ingredients that may not be suitable, and some people may react poorly to caffeine on an empty stomach.

A 'clean' fast is a strict fasting approach that only allows for plain water. It avoids all calories, artificial sweeteners, and other additives to ensure the body remains in a complete fasted state, maximizing benefits like cellular repair (autophagy).

Safe and fasting-friendly drink alternatives include plain water, sparkling water (unflavored), black coffee, and unsweetened green or herbal tea.

Yes, some people report that the sweet taste of artificial sweeteners can trigger cravings and a cephalic-phase insulin response, which can lead to increased hunger, making it harder to stick to a fast.

A 'dirty fast' involves consuming a minimal number of calories or ingredients that might technically break a fast. For those focused purely on a calorie deficit for weight loss, the small potential impact might be acceptable, but it still risks disrupting key metabolic processes.

Since it does not contain carbohydrates, 0 calorie Red Bull is unlikely to directly pull you out of ketosis. However, if the artificial sweeteners cause an insulin spike, it could temporarily inhibit some of the fat-burning benefits associated with ketosis.