Hunt for ‘natural’ no-calorie sweetness puts a spotlight on stevia
Stevia followers are a diverse bunch, including health nuts and food-industry magnates. The draw? The sweetener is all-natural and naturally calorie-free. But “natural” doesn’t necessarily mean safe, and scientists have long struggled to make sense of early evidence hinting that stevia could be toxic. A series of studies published last month in the journal Food and Chemical Toxicology put that question to the test for one type of stevia-based sweeteners.
Stevia, a South American shrub, has leaves up to 300 times sweeter than table sugar. Extracts have been available as a dietary supplement since 1995. It’s a popular food additive in Japan, Brazil and its native Paraguay, but in the U.S., where the Food and Drug Administration has determined there isn’t sufficient proof it’s nontoxic, stevia is banned from such uses. (Exceptions are made for food and drink items billing themselves as dietary supplements, such as the stevia-sweetened diet drink Zevia.)
The sponsors of the recently published studies -- food manufacturer Cargill and the Coca-Cola Co. -- hope that in light of recent findings, the agency will reconsider its position on the calorie-free sweetener.
Scientists began studying stevia in the lab roughly 40 years ago, and the first findings gave food safety officials in several countries pause. A 1968 study in female rats showed that drinking a concoction of stevia leaves and stems significantly reduced fertility. A 1985 study, published in the Proceedings of the National Academy of Sciences, showed that steviol, a breakdown product of stevia, might cause genetic mutations. (In Paraguayan traditional medicine, stevia is used to lower blood sugar and as a contraceptive.)
Evidence of genetic and reproductive toxicity was sufficient to inspire a ban on the sweetener in the U.S. since the 1970s. (The 1994 Dietary Supplement Health and Education Act made it legal to sell stevia as a dietary supplement only, as long as it’s not an ingredient in food.) But the research on which the FDA based its long-ago decision may now be out of date. In the last decade, countless studies have revisited stevia, often using purer extracts.
The more-recent research has largely focused on purified forms of the two main chemicals responsible for the stevia plant’s sweetness: stevioside and rebaudioside A. Findings from some studies -- still few in number -- have resulted in a perhaps overstated claim: that stevia lowers blood pressure.
For example, a 2000 study of 100 adults in Taiwan showed that 250 milligrams of stevioside a day lowered subjects’ blood pressure by 8% to 12% within three months. A 2003 Chinese study in which nearly 170 adults were given 1,500 mg of stevioside daily in three 500 mg doses also reported that subjects’ blood pressure went down. (Both doses are far greater than the amount of stevioside in the few grains of powdered stevia it takes to sweeten a cup of tea.)
Authors of a 2006 report by the World Health Organization acknowledged the promise of the blood pressure studies. The authors also reviewed the dozens of lab and animal studies that had been done on stevioside and rebaudioside A in recent years -- and concluded that the compounds appear unlikely to harm DNA or the reproductive system.
The eight studies published in Food and Chemical Toxicology last month went even further. One report showed no reproductive toxicity in rats exposed to the sweetener for two generations, and two human studies showed that 1,000 mg of rebaudioside A per day was safe for healthy adults as well as those with Type 2 diabetes. Rebaudioside A (dubbed Rebiana by Coca-Cola and Cargill) is “safe for human consumption,” three of the study authors wrote. They did not report on stevioside.
These latest findings -- should the FDA find them compelling -- may be good news for food manufacturers, which have long sought a natural zero-calorie sugar alternative to market to the calorie-conscious public.
But some aren’t convinced it’s good news for consumers just yet. Michael Jacobson, executive director of the Center for Science in the Public Interest Group, a Washington, D.C.-based nutrition advocacy group, said the research still hasn’t quelled concerns about stevia’s genetic toxicity. Although dozens of studies have shown stevia compounds to be harmless, a handful suggest it can damage genetic material. “It’s a warning flag,” he said.
Jacobson added that genetic toxicity may turn out to be attributable to a specific species or component of stevia. Cargill, meanwhile, is certain that at least one stevia component is safe. Rebaudioside A, under the brand name Truvia, is already on store shelves in New York as a test, with the FDA’s blessing. Consumers can expect to see it across the country this fall -- if the FDA agrees.