Kombucha, a popular fizzy fermented tea, is often perceived as a healthy beverage, but its impact on blood sugar levels warrants a closer look, especially given that it always contains added sugars essential for the fermentation process. While sugar-sweetened drinks like soda are known to cause rapid blood sugar spikes, experts and research suggest that kombucha may behave differently due to its unique composition and the fermentation process itself.

Typically, kombucha contains between 3 and 15 grams of sugar per serving, which can be comparable to some sports drinks at the higher end. Sugary beverages usually lead to quick increases in blood sugar because their concentrated sugars are rapidly absorbed into the bloodstream, lacking the protein, fiber, or fat that slow digestion in solid foods. However, a crucial distinction for kombucha is that a significant portion of the sugar initially added is broken down by yeast and bacteria during fermentation. This means the final product generally contains less sugar than the original mixture, as explained by Erin Palinski-Wade, RD, CDCES, author of 2 Day Diabetes Diet.

This reduction in actual sugar content may contribute to why some studies indicate kombucha has a less pronounced effect on blood sugar compared to other drinks with similar initial sugar levels. For instance, a small 2023 study observed that individuals who consumed kombucha (containing 1.7 grams of sugar) alongside a high-carbohydrate meal experienced significantly lower blood sugar levels than those who drank sugar-free beverages. The beneficial effects are thought to stem from fermentation byproducts such as organic acids, ethanol, and various other metabolites. According to registered dietitian and food scientist Jennifer Pallian, BSc, RD, these compounds can slow the rate at which glucose enters the bloodstream by delaying stomach emptying and reducing carbohydrate digestion. Additionally, kombucha's antioxidants might further aid in slower sugar absorption and enhance insulin sensitivity, thereby helping to stabilize blood sugar rather than causing spikes, Palinski-Wade noted.

Despite these promising findings, the overall research on kombucha and blood sugar has been described as "inconsistent" by a 2025 review. Furthermore, some studies showing positive results, including the aforementioned one, have faced limitations such as small sample sizes and potential conflicts of interest due to industry funding.

The key takeaway is that while kombucha might have a less detrimental effect on blood sugar compared to other sugary drinks, its sugar content still needs to be considered. Consuming it excessively throughout the day can lead to an accumulation of sugar, which, regardless of its source, is advised to be kept in check. The Dietary Guidelines for Americans recommend limiting added sugars to no more than 10% of total daily calories, or about 50 grams for a 2,000-calorie diet. While some kombucha brands have higher sugar content, it generally contains less than soda, making it a potentially healthier alternative for regular soda drinkers. Its beneficial bacteria and antioxidants could also offer unique blood sugar benefits over other sweetened beverages. Experts like Palinski-Wade suggest limiting kombucha intake to approximately 8 ounces per day. Individuals with health conditions such as insulin resistance, prediabetes, or type 2 diabetes should consult their doctor about incorporating kombucha into their diet. Moreover, pregnant individuals, those who are immunocompromised, or those needing to avoid unpasteurized foods should refrain from consuming kombucha entirely. Palinski-Wade also points out that kombucha can contain small amounts of alcohol and caffeine, advising caution for anyone sensitive to these substances or taking medications that may interact with them.