Can I drink zero sugar soda while intermittent fasting?

November 28, 2025 •

5 min read

According to a 2019 review, there is no consistent link between low-calorie sweetener intake and increased body weight, yet many still question if zero sugar soda breaks a fast. This article explores the science behind the question: Can I drink zero sugar soda while intermittent fasting?

Quick Summary

Zero sugar soda's effects on fasting vary by individual and goals, as artificial sweeteners may trigger an insulin response or increase cravings, potentially disrupting some metabolic benefits.

Key Points

Not all fasts are equal: For weight loss through calorie control, zero sugar soda is less disruptive than for metabolic health goals like insulin sensitivity or autophagy.
Artificial sweeteners are a gray area: While zero-calorie, sweeteners like aspartame and sucralose might trigger a small insulin response in some individuals, potentially hindering fat burning.
Autophagy is the most sensitive goal: If maximizing cellular cleanup (autophagy) is your priority, avoid all sweeteners, as some, like aspartame, can inhibit this process.
Listen to your body: Individual responses vary greatly; some people experience increased cravings from diet sodas, while others don't. Experiment and see how it affects your hunger and energy levels.
Safe alternatives exist: For a flavored fix, stick to plain sparkling water, black coffee, or unsweetened teas to ensure a 'clean fast' and avoid metabolic interference.
Mind the gut: Some research suggests artificial sweeteners can alter the gut microbiome, which is detrimental to overall health.

The Dilemma: Calories vs. Metabolic Response

When practicing intermittent fasting (IF), the primary goal is often to induce a metabolic state where the body burns stored fat for energy, not just restrict calories. This happens when insulin levels are kept low for a sustained period. Zero sugar soda presents a dilemma because it contains no calories, but the artificial sweeteners within can have other metabolic effects. While a zero-calorie drink technically won't break a fast from a purely caloric perspective, experts debate whether the sweet taste and chemical composition of artificial sweeteners disrupt the fasting state by triggering an insulin response.

The Impact of Artificial Sweeteners

Artificial sweeteners like aspartame, sucralose, and saccharin are key ingredients in most zero sugar sodas. The question is whether these non-caloric substances can 'trick' the body into thinking sugar is coming, causing a cephalic phase insulin response.

Insulin Response: Some studies, though not all, suggest artificial sweeteners might provoke a small insulin release in some individuals. This response varies widely from person to person, influenced by metabolism and gut microbiome. For those fasting specifically to improve insulin sensitivity, even a minor spike could be counterproductive.
Gut Microbiome: Research indicates that artificial sweeteners can negatively alter the balance of gut bacteria. A disrupted microbiome has been linked to metabolic issues and inflammation, which are contrary to the health-promoting goals of fasting.
Cravings and Appetite: The sweet taste without corresponding calories can confuse metabolic signaling. This can increase hunger and cravings for sugary foods later on, potentially making it harder to adhere to your eating window and leading to overeating.
Autophagy and Longevity: For those fasting for longevity and cellular repair (autophagy), avoiding all sweeteners is the safest approach. Aspartame, in particular, is metabolized into amino acids that can stimulate growth pathways (mTOR) and inhibit autophagy.

Alternatives to Zero Sugar Soda

For those who find themselves craving a flavored drink during their fast, several safer alternatives exist that are less likely to disrupt the metabolic benefits of fasting. The key is to choose options that are completely free of calories and sweeteners.

Water: Plain still or sparkling water is the gold standard for hydration during a fast. Sparkling water can also help satisfy the craving for a fizzy drink.
Black Coffee: Contains minimal calories and may even enhance fat oxidation.
Unsweetened Tea: Green, black, or herbal teas without additives are safe. Green tea contains antioxidants that can aid fasting benefits.
Infused Water: Add a slice of lemon, lime, or some mint leaves to plain water for flavor without calories or sweeteners.

Comparison of Common Sweeteners and Fasting Goals

To help you decide, here is a comparison table outlining the effects of different zero-calorie sweeteners based on common fasting goals.


Sweetener Type	Primary Fasting Goal	Caloric Impact	Potential Insulin Effect	Gut Health Impact	Autophagy Effect	Verdict During Fast	Authoritative Source
Stevia	Metabolic health, weight loss, longevity	None	Minimal to none	Neutral to potentially beneficial	Safe	Generally OK, best in moderation
Erythritol	Metabolic health, weight loss	Minimal (0.2 kcal/g)	None	Disrupts gut rest	Safe	OK for weight loss, not for gut rest
Aspartame	Weight loss	Minimal	Minor/Variable	Possible negative change	Inhibits autophagy	Avoid, especially for autophagy
Sucralose (Splenda)	Weight loss	None	Potential small spike	Possible negative change	Potential disruption	Avoid, especially for metabolic health

What Science Says About Artificial Sweeteners

While the caloric content of zero sugar sodas might not technically break a fast, the scientific debate centers on the metabolic response to artificial sweeteners. Research on this topic is still evolving and shows mixed results, with individual differences being a key factor. Some studies suggest potential long-term negative effects on gut health, insulin sensitivity, and appetite regulation. The World Health Organization has also released cautious guidelines regarding the use of non-sugar sweeteners, noting they may not provide significant long-term weight loss benefits. Ultimately, a clean fast, which only includes water, black coffee, or plain tea, eliminates all doubt and potential metabolic interference.

Making an Informed Decision

The decision of whether to include zero sugar soda in your intermittent fasting routine comes down to your personal health goals and how your body reacts. If your main goal is weight loss through simple calorie restriction and you find that diet soda helps you stick to your fasting schedule by curbing cravings, the occasional one may be acceptable. However, if you are pursuing deeper metabolic benefits, such as improving insulin sensitivity or maximizing autophagy, the potential risks of artificial sweeteners suggest avoiding zero sugar soda entirely during your fasting window.

To find what works for you, consider a personal test. Try a week of fasting without any zero sugar soda and track your energy levels, cravings, and overall feeling. Then, compare it to a week where you include it. Pay close attention to any changes in appetite or other symptoms. Listening to your body is crucial for optimizing your fasting strategy.

Conclusion

While a zero sugar soda won't technically break a fast from a calorie-intake perspective, the artificial sweeteners can provoke unwanted metabolic responses that may hinder your fasting goals. The potential for a minor insulin spike, disruption of gut health, and increased cravings means that for those seeking maximum metabolic benefits like autophagy and improved insulin sensitivity, clean fasting is the safer and more effective path. For individuals primarily focused on weight loss and using it as a tool to adhere to their fasting schedule, occasional consumption may be acceptable. The best strategy is to listen to your body and prioritize water, coffee, and unsweetened tea for optimal fasting results.

For more information on the health benefits of intermittent fasting, a great resource can be found at Johns Hopkins Medicine.

What to drink instead

Plain Water: Still, sparkling, or mineral water contains zero calories and is excellent for hydration.
Black Coffee: Unsweetened, black coffee is permissible and can help curb hunger.
Unsweetened Tea: Green, black, and herbal teas can provide flavor without breaking a fast.
Infused Water: Flavor water naturally with slices of lemon, lime, or cucumber.
Diluted Apple Cider Vinegar: A small amount can be added to water for flavor and potential metabolic benefits.

Frequently Asked Questions

Diet Coke contains artificial sweeteners like aspartame that may trigger a small insulin response in some people, potentially hindering the metabolic benefits of fasting like fat burning. For strict fasting, it's best to avoid it.

It is not recommended, as zero-calorie energy drinks contain artificial sweeteners that can potentially trigger an insulin response. The high caffeine content can also cause anxiety and disrupt sleep, which is important for hormone regulation during a fast.

Zero-calorie flavored water is generally acceptable as long as it contains no sweeteners that might cause an insulin response. However, plain water is the safest option. Some flavored waters may use low-calorie sweeteners, so it is best to check the ingredients.

Yes, some artificial sweeteners found in diet sodas, like aspartame and sucralose, have been shown to negatively impact the gut microbiome. For those seeking gut rest benefits from fasting, it's best to avoid them.

Plain water (still or sparkling), black coffee, and unsweetened tea are the best drinks for intermittent fasting. They provide hydration without calories or sweeteners that can disrupt the fasting state.

Stevia is a non-caloric sweetener and generally considered a safer alternative to artificial sweeteners. However, some very strict fasters prefer to avoid all sweet tastes to prevent any potential metabolic or craving-related effects.

The sweet taste of diet soda without any actual sugar can confuse the body's metabolic signaling. This can trigger a release of appetite-stimulating hormones and potentially lead to increased cravings for high-sugar foods later on.

Clean fasting refers to a fasting protocol where only water, black coffee, and plain unsweetened tea are consumed. This eliminates any potential metabolic disruption from sweeteners or additives, maximizing benefits like improved insulin sensitivity and autophagy.

Bone broth is not zero-calorie and contains small amounts of protein and fat. While it is a popular option in some modified fasting protocols, it will break a strict fast aimed at achieving maximum autophagy or metabolic rest.