Amid growing concerns about artificial sweeteners, many of my readers asked whether stevia can also change gut bacteria. Stevia is a sugar substitute extracted from the leaves of a plant, Stevia rebaudiana, and is almost 200 times sweeter than regular table sugar. In 2008, the FDA declared that stevia was safe in foods and beverages. Since it is taken in such small quantities and is not absorbed in the upper intestinal tract, it does not raise blood sugar levels. However, very little research has been done on its effect on gut bacteria. Stevia passes to the colon where it is fermented by bacteria into glucose (an absorbable sugar), and then into steviol, a sugar alcohol which passes out in the stool. One study showed that stevia reduces the number of beneficial bacteria such as Lactobacillus reuteri, which may increase risk for diabetes and weight gain (Letters in Applied Microbiology, 2014;58.3: 278-284). Lactobacillus reuteri helps to prevent heart attacks by lowering cholesterol (European Journal of Clinical Nutrition, 66.11 (2012): 1234-1241), and is used to treat diarrhea in children (Journal of Pediatric Gastroenterology and Nutrition, 24.4 (1997): 399-404). However, another study found stevia did not change human fecal cultures incubated with either stevioside or rebaudioside A (Journal of Agricultural and Food Chemistry, 2003;51(22): 6618-6622).
Stevia Products are Often Adulterated
If you want to use stevia, make sure you read the list of ingredients on the label. Truvia, a popular brand of sweetener that claims to contain stevia, also contains erythritol, a sugar alcohol, and “natural flavors”. Pyure, another stevia product, also contains dextrose, a starch-derived glucose which is often extracted from corn, wheat or rice. Other brands may contain sugar alcohols that can change your intestinal bacteria to favor those that increase risk for weight gain (check the list of ingredients!). When stevia is used to sweeten foods and drinks, manufacturers often add other sweetening ingredients as well.
All No-Calorie Sweeteners Lie to Your Brain
I suggest trying to break the habit of sweetening drinks and learn to quench your thirst with water or a non-sweetened beverage such as tea or coffee. Stevia is unlikely to be any more beneficial than any of the “artificial” sweeteners for weight loss, weight control or prevention of diabetes. Many research papers show that no-calorie sweetened drinks are associated with increased risk for weight gain, diabetes and heart attacks. Of 66,188 women followed for 14 years, those who used diet drinks rather than sugar-sweetened drinks had a higher risk of diabetes (American Journal of Clinical Nutrition, February 7, 2013). Interestingly, the women who drank artificially-sweetened drinks took in more (average of 2.8 glasses/day) than those who took sugared drinks (1.6 glasses/day). The San Antonio Heart Study showed that drinkers of artificially-sweetened beverages consistently weighed more than those who do not drink diet drinks (Obesity, 2008;16:1894–1900). An American Cancer Society study showed that no-calorie sweetened drink users gain far more weight than non-users (Prev Med, 1986;15:195–202). These studies do not show that no-calorie sweeteners cause weight gain, heart attacks or diabetes; people who are overweight are likely to be using these products in an effort to lose weight and decrease their risk for diabetes or heart attacks. However, other studies show that the artificial sweeteners may be harmful rather than helpful for people who are trying to lose weight.
I will watch for further research on stevia, but meanwhile, I suggest that if you want to use it, grow your own (one small plant will give you plenty) or buy it in dried-leaf form where you can see what you are consuming. Once stevia is reduced to a powder and packaged for sale in packets, pellets or as part of another food product, you have no idea what you are actually getting.