Are There Downsides to the Sweetener Stevia?

Major health and food safety organizations generally regard stevia, a sweetener made from a plant native to South America, as safe. But some researchers warn that we don’t have enough evidence to fully understand how products like stevia, so-called nonnutritive sweeteners that have no calories, affect the body.

Ounce for ounce, stevia is 200 to 400 times sweeter than table sugar, so a small amount can add a lot of sweetness. Stevia is found in products like soda and iced tea, sweetener packets with names like Truvia and Pure Via, and foods marketed as low sugar, such as ice cream and yogurt.

Stevia sweeteners are purified extracts of one type of constituent, called steviol glycosides, found in the leaves of the stevia plant. The European Food Safety Authority and the World Health Organization both say these compounds are safe in the amounts typically used. This conclusion is based on studies — mostly industry funded — in bacteria and rodents that generally show that stevia doesn’t cause damage to DNA or cancer, as well as several human studies that found no effect on blood pressure or blood glucose.

The Center for Science in the Public Interest, a food advocacy group that has often been critical of sugar substitutes, initially raised concerns about stevia sweeteners when they came onto the market in 2008, saying the Food and Drug Administration should have required more testing. However, the group ranked stevia as one of the safest of the sugar substitutes in a 2014 report, in part because it has a long history of use in Japan.

Stevia sweeteners are broken down by bacteria in the large intestine, but gastrointestinal symptoms like bloating and diarrhea haven’t been reported in studies. However, some products containing stevia also include sugar alcohols like erythritol, which can cause digestive complaints if consumed in large amounts.

Using stevia is a reasonable strategy to reduce the amount of sugar we consume, said Marina Chaparro, a registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics. “It has the flavor without adding the extra sugar and affecting your blood sugar,” which is especially useful for those with diabetes, she said. She also recommends other strategies to reduce sugar intake, like adding fresh fruit to oatmeal instead of sugar and drinking flavored water instead of soda.

It’s uncertain, though, whether using calorie-free sweeteners like stevia can reduce caloric intake. A recent small study found, for example, that when participants had a drink sweetened with stevia instead of sugar in the morning, they compensated by eating more at lunch, along with bigger lunchtime spikes in blood glucose and insulin.

And some researchers worry that long-term use of nonnutritive sweeteners could have unintended metabolic effects that might not be detected using standard toxicological tests or other measures. “Over all, for nonnutritive sweeteners, we lack evidence, but that’s especially true for stevia,” which has not been extensively studied, said Meghan Azad, assistant professor of pediatrics and child health at the University of Manitoba.

Dr. Azad was the lead author of a recent review of long-term use of nonnutritive sweeteners that concluded that they may not be helpful for weight loss and, in some studies, were associated with increased incidence of obesity, diabetes and heart disease. She and her co-authors, however, found no long-term studies of stevia in particular to include in that review.

Additional research is questioning how these sweeteners might affect our gut microbes or if the taste of sweetness without the reward of calories could alter regulation of energy intake and response to sugar consumption.

These concerns are preliminary, says Dr. Azad, and we need more research. But, she said, “Just blindly assuming that these are a healthy alternative to sugar is probably not a wise move without the evidence to back it up.”

By Alice Callahan