Pepsi Zero Sugar has zero calories, zero grams of sugar, and zero grams of carbohydrates, making it technically compatible with a ketogenic diet. It won’t contribute any carbs toward your daily limit, and drinking it shouldn’t knock you out of ketosis. That said, the details matter if you care about what’s in your glass beyond the macros.
What’s Actually in Pepsi Zero Sugar
The ingredient list is straightforward for a diet soda: carbonated water, caramel color, phosphoric acid, aspartame, potassium benzoate (a preservative), caffeine, natural flavor, acesulfame potassium, citric acid, calcium disodium EDTA, and panax ginseng root extract. The two sweeteners doing the heavy lifting are aspartame and acesulfame potassium (often called Ace-K), which combine to mimic the taste of sugar without adding calories or carbs.
One thing that stands out is the caffeine. A 12-ounce can of Pepsi Zero Sugar contains roughly 69 mg of caffeine, nearly double the 37 mg in regular Pepsi and the 35 mg in Diet Pepsi. If you’re drinking multiple cans a day or pairing them with coffee, that adds up quickly.
Do the Sweeteners Affect Ketosis?
The biggest concern people have with diet sodas on keto is whether artificial sweeteners trigger an insulin response that could interfere with fat burning. The available clinical evidence is reassuring on this point. A 12-week study reviewed by Diabetes.co.uk found no significant difference in insulin sensitivity or insulin secretion between periods when participants consumed artificial sweeteners and when they didn’t. In practical terms, aspartame and Ace-K don’t appear to raise insulin in a way that would stall ketosis.
This is different from some other sweeteners. Maltodextrin, for example, spikes blood sugar. Sugar alcohols like maltitol still have a meaningful glycemic impact. Aspartame and Ace-K sit at the safer end of the spectrum for keto purposes because they pass through your body without being metabolized into glucose.
The Gut Microbiome Question
Where things get more nuanced is gut health. Research published in ScienceDirect shows that artificial sweeteners, including Ace-K and aspartame, can influence the composition of gut bacteria. Saccharin appears to have the strongest effect, but Ace-K and aspartame also alter bacterial behavior and growth at concentrations people actually consume. Some of these changes have been linked to shifts in the body’s glycemic response, meaning how well you process sugar when you do eat it.
This doesn’t mean Pepsi Zero will ruin your gut. But if you’re drinking several cans daily over months, the cumulative effect on your microbiome is worth considering, especially since people on keto already experience shifts in gut bacteria from the dramatic reduction in fiber-rich carbohydrates.
Clean Keto vs. Dirty Keto
Whether Pepsi Zero “counts” as keto depends on which version of keto you follow. The keto community generally splits into two camps. Clean keto emphasizes whole, nutrient-dense foods and minimizes processed ingredients. Under those rules, Pepsi Zero is an occasional indulgence at best. It provides no vitamins, no minerals, and nothing your body can use as fuel or building material.
Dirty keto (sometimes called lazy keto) focuses purely on hitting your macronutrient targets: high fat, moderate protein, very low carbs. Under this framework, Pepsi Zero is perfectly fine. Zero carbs means zero impact on your daily carb budget, and that’s the only metric that matters. Most people practicing keto casually fall somewhere between these two approaches, and an occasional Pepsi Zero won’t derail either version.
Aspartame Safety at a Glance
In 2023, the International Agency for Research on Cancer classified aspartame as “possibly carcinogenic to humans,” a category that sounds alarming but is based on limited evidence, specifically a small association with liver cancer that hasn’t been confirmed. At the same time, the WHO’s Joint Expert Committee on Food Additives reviewed the data and reaffirmed the existing safe intake limit of 40 mg per kilogram of body weight per day.
To put that in perspective, a can of diet soda typically contains 200 to 300 mg of aspartame. A 154-pound adult would need to drink more than 9 to 14 cans per day to exceed the safe limit, assuming no aspartame from any other food source. For most people, even heavy diet soda consumption falls well within the safety margin.
Practical Tips for Keto Soda Drinkers
If you’re going to include Pepsi Zero in your keto routine, a few things are worth keeping in mind. First, carbonated drinks can increase feelings of bloating, which some people on keto already experience during the adjustment period. Spacing out your intake rather than drinking multiple cans in a sitting helps.
Second, the caffeine content is meaningful. At 69 mg per can, two Pepsi Zeros give you more caffeine than a standard cup of coffee. If you’re sensitive to caffeine or drinking these in the afternoon, it could affect your sleep, which in turn affects the hunger hormones that make sticking to any diet harder.
Finally, some people find that the sweet taste of diet soda, even without real sugar, keeps sugar cravings alive. This is anecdotal and varies from person to person, but if you notice that drinking Pepsi Zero makes you want to reach for something sweet afterward, it may be working against you psychologically even if the macros check out.