Can I drink Pepsi in fast? A definitive look at soda, sweeteners, and your fasting goals

October 14, 2025 •

4 min read

According to the National Center for Biotechnology Information, nearly half of American adults consume low or zero-calorie sweeteners, making the question, "Can I drink Pepsi in fast?" a common one for those following a fasting diet. The answer depends entirely on the type of Pepsi and your specific health goals, with regular soda containing calories that will break a fast, and diet versions presenting a more complex metabolic challenge.

Quick Summary

This article explores the nutritional implications of consuming regular and diet soda during a fasting window, examining how sugar and artificial sweeteners impact metabolic states, insulin response, and overall fasting benefits. It provides clear guidance on which beverages are best for maintaining a fasted state and offers a comparison of different drink options.

Key Points

Regular Pepsi breaks a fast: Due to its high sugar and calorie content, regular Pepsi immediately ends any fasted state by spiking blood sugar and insulin.
Diet Pepsi's impact is debated: While technically zero-calorie, diet soda's artificial sweeteners can trigger a metabolic response and potentially interfere with fasting's deepest benefits.
Consider your fasting goals: For maximum metabolic benefits like autophagy and optimal insulin sensitivity, avoiding all sweeteners during fasting is recommended.
Pay attention to your body: Some people experience increased cravings or digestive issues from artificial sweeteners, making adherence to a fast more difficult.
Stick to clean alternatives: The safest and most effective beverages for fasting are water, black coffee, unsweetened tea, and plain sparkling water.
Artificial sweeteners can affect insulin: Despite not containing calories, artificial sweeteners can trigger an insulin release in some individuals, which inhibits fat burning.
Diet soda may impact gut health: Research suggests that artificial sweeteners can negatively alter the gut microbiome, potentially affecting overall metabolic health.

The difference between regular and diet Pepsi

Understanding the distinction between regular and diet sodas is the first step to knowing how they affect a fast. Regular Pepsi is loaded with sugar and calories. A standard can contains over 150 calories and dozens of grams of sugar. Consuming this would immediately break any form of fast, as your body would shift from burning stored fat for energy to processing the new influx of glucose. It is a clear and definitive 'no' for anyone aiming to maintain a fasted state for weight loss or other metabolic benefits.

Diet Pepsi, on the other hand, contains artificial sweeteners like aspartame and acesulfame potassium and is marketed as having zero calories. This is where the topic becomes more complex and the consensus is divided, particularly in the intermittent fasting community. While diet soda doesn't contain the caloric energy needed to truly break a fast in the traditional sense, the effect of artificial sweeteners on your body is still a subject of scientific debate.

The metabolic impact of artificial sweeteners

Even without calories, artificial sweeteners can have a significant effect on your body's metabolic processes. The sweet taste alone can trigger a "cephalic phase" response, where your body prepares for incoming food by releasing digestive hormones and, potentially, a small amount of insulin. Insulin is a potent inhibitor of fat metabolism, and even a minor spike could diminish the fat-burning benefits of fasting.

Impact on hunger and cravings

Artificial sweeteners have been shown in some studies to increase sugar cravings and appetite. The sweet taste without a caloric reward can confuse the body's hunger signals. This might lead to increased hunger pangs, making it more challenging to stick to a fasting window. For someone using fasting to manage cravings and caloric intake, this could be a major setback.

Effects on gut health

There is also ongoing research into the effects of artificial sweeteners on the gut microbiome. Some studies suggest that regular consumption of certain sweeteners, including aspartame and sucralose, can negatively alter the balance of gut bacteria, which can impact metabolism and overall health. Since a healthy gut is linked to better metabolic function, disrupting it can undermine the very health benefits fasting aims to achieve.

Fasting goals and individual responses

Your specific reason for fasting plays a crucial role in deciding whether diet Pepsi is an acceptable beverage. For a clean fast, which prioritizes metabolic and cellular health benefits like autophagy (cellular cleanup), avoiding all non-water beverages is the strictest approach. However, for those primarily focused on weight loss through calorie restriction, the potential impact might be negligible, and a diet soda could help with adherence.

It's also important to remember that individual responses to artificial sweeteners vary. What minimally impacts one person's insulin levels might have a more noticeable effect on another. The best approach is to observe your own body. If you notice increased cravings or digestive discomfort after consuming diet soda, it may be best to avoid it during your fasting periods.

Fasting-friendly alternatives to soda

For those seeking a fizzy alternative to Pepsi that won't compromise a fast, there are several options available. These beverages provide hydration and can satisfy a craving for carbonation without the associated metabolic risks of artificial sweeteners.

Plain Water: The absolute gold standard for hydration during a fast. It has zero calories, zero additives, and won't affect insulin levels.
Sparkling Water: For that carbonated feeling, plain sparkling or seltzer water is a great choice. Opt for brands with no sweeteners or additives. Some brands offer natural essences (like a hint of citrus) which are generally considered safe.
Black Coffee: Unsweetened, black coffee is a popular choice during fasting. The minimal calories are typically not enough to break a fast, and its caffeine content can help with energy levels and appetite suppression.
Unsweetened Tea: Green, black, and herbal teas (without added sweeteners or milk) are excellent alternatives. They offer flavor variety with minimal to no caloric content and may provide additional health benefits.

Regular vs. Diet Pepsi vs. Water: A comparison for fasters


Feature	Regular Pepsi	Diet Pepsi	Plain Water
Calories	High (over 150 per can)	Effectively Zero	Zero
Sweeteners	Sugar (High Fructose Corn Syrup)	Artificial (Aspartame, Acesulfame K)	None
Impact on Fast	Breaks fast immediately. Spikes blood glucose and insulin.	May disrupt fast. Sweet taste can trigger an insulin response and affect gut health, depending on individual response and goals.	Ideal for fasting. No metabolic impact, supports hydration.
Cravings	Leads to sugar crashes and subsequent cravings.	May increase sugar cravings in some individuals.	Does not increase cravings.
Nutritional Value	None beyond sugar.	None. Contains artificial additives.	Essential for hydration and bodily functions.

Conclusion

The question of "can I drink Pepsi in fast?" has a simple answer for the regular, sugar-filled version: no, it will immediately break your fast due to its high caloric and sugar content. The answer for Diet Pepsi is more complicated and depends on your individual fasting goals and metabolic sensitivity to artificial sweeteners. For those seeking the deepest metabolic benefits of fasting, such as improved insulin sensitivity and autophagy, avoiding diet sodas is the safest bet. Opting for healthier, non-sweetened alternatives like water, sparkling water, black coffee, or tea ensures a clean fast without potential metabolic interference. Ultimately, listening to your body's response to different beverages is the most effective strategy for a successful fasting journey.

For a deeper dive into the science behind artificial sweeteners, you can explore research from the National Center for Biotechnology Information on the subject.

Frequently Asked Questions

No, you cannot drink regular Pepsi while intermittent fasting. It contains a significant amount of sugar and calories that will immediately break your fast, ending the metabolic benefits you are seeking to achieve.

The answer is debated and depends on your specific goals. While Diet Pepsi is calorie-free, its artificial sweeteners may trigger a metabolic response, such as a mild insulin release, which could interfere with fat burning and other fasting benefits.

Some people believe that the artificial sweeteners in diet soda, like aspartame, can trick the body into an insulin response. This would interrupt key metabolic processes like autophagy and sustained fat burning, which are central to many fasting protocols.

Yes, there are many healthy alternatives. Opt for plain water, unsweetened black coffee, unsweetened tea, or plain sparkling water. These beverages contain no calories or sweeteners and won't interfere with your fasting state.

If your primary goal is weight loss through calorie restriction, an occasional diet Pepsi might not significantly impact your overall progress. However, be aware it could increase cravings for other sweet foods, making it harder to stick to your dietary plan.

Autophagy is a cellular cleanup process that is one of the key benefits of fasting. Some experts believe that even a minor insulin spike from artificial sweeteners could potentially interfere with autophagy, though more research is needed.

Plain sparkling water with natural essences and no sweeteners is generally considered acceptable during a fast. Always read the label to ensure no artificial sweeteners or caloric additives have been included.