The Science Behind Stevia

The sweetener stevia has plenty of dedicated followers. Who can blame them? For years, food and supplement manufacturers have advertised stevia as all natural, calorie free and safe for people with diabetes. To many people, stevia seems like a win-win: It sweetens food without adding calories, and it seems to be a healthy alternative to artificial sweeteners. But can you really believe all the hype?

The History of Stevia: From Supplement to Sweetener
Stevia is derived from the leaves of a South American shrub called Stevia rebaudiana. Its green leaves contain a substance that is 250-300 times sweeter than table sugar. The leaf extracts have been used for years in Brazil, Paraguay, Japan, South Korea, and China to sweeten foods in small to moderate amounts.

About 40 years ago, scientists began to study stevia in a laboratory setting. Some studies showed that stevia may reduce fertility or cause genetic mutations that could lead to cancer. In the 1970s, it was banned as a food ingredient in the United States. Then in 1994, the Dietary Supplement Health and Education Act made it legal to sell stevia in the United States as a dietary supplement only. Unlike foods, supplement manufacturers are not required to prove that their products are safe for consumption. For more than a decade, stevia powders, liquids and extracts were sold, usually in health food stores, as supplements, not foods. During this time, companies could not sell or market stevia as a food or an ingredient in any food product.

In 2004, the Joint Expert Committee on Food Additives of the Food and Agriculture Organization of the United Nations and the World Health Organization, an international regulatory authority, re-evaluated the research on stevia and requested additional information from ongoing toxicological and clinical studies. 

There are two main sweetening chemicals in the stevia leaf: Rebaudioside A (also called Reb A or Rebiana) and stevioside. These two purified forms have received the most recent research. The July 2008 journal Food and Chemical Toxicology published eight studies on stevia. (You can obtain abstracts from these published studies through One report showed no reproductive toxicity in rats exposed to the sweetener for two generations, and two human studies showed that 1,000 milligrams of Rebaudioside A per day was safe for healthy adults, as well as those with Type 2 diabetes. They did not report on stevioside.

Around this time, several food manufacturers petitioned the U.S. Food and Drug Administration, stating that they consider Rebaudioside A (the highly purified extract of stevia) to be "GRAS" (Generally Recognized as Safe). When the FDA adds a food (or ingredient) to the GRAS list, it can be sold in foods and as a food product, even without prior FDA approval and without definitive proof that the food actually is safe.

In December 2008, the FDA concluded that Rebausioside A, the highly purified form of the leaves of the stevia plant, could have GRAS status as a general-purpose sweetener in foods and beverages. That means that stevia is no longer a supplement. You can now find it in the baking aisle, next to other sugars and artificial sweeteners. It is also an ingredient in some foods and beverages, used much like artificial sweeteners are, in diet soda, diet drinks, pudding, yogurt and other food products.

Not all food and nutrition experts are content with this research or with the FDA's ruling to add stevia to the GRAS list. Michael Jacobson, executive director of the Center for Science in the Public Interest, is encouraging more testing. While Jacobson doesn't say that stevia is harmful, he doesn't think it should be marketed until new studies establish that it is safe. (To see CSPI's stance, along with Jacobson's letter to the FDA, click here.)

Despite lingering controversy, food manufacturers didn't waste any time bringing this zero-calorie sweetener to the public. As we are publishing this article (Feb. 2009), three companies sell stevia on your grocery shelf:

  • Truvia (from Coca-Cola and Cargill) is marketed as a tabletop sweetener. The Coca-Cola company will also sweeten Sprite Green and Odwalla juice drinks with Truvia.
  • PureVia (from PepsiCo and Whole Earth Sweetener Co.) is marketed as a tabletop sweetener, and Pepsi will use it as a sweetener in three flavors of SoBe Lifewater.
  • Sweetleaf by Wisdom Natural Brands started selling in the summer of 2008.
This Dietitian’s View
Adults should consume no more than four artificially sweetened products daily, and that includes products sweetened with stevia. This guideline gives you the freedom to enjoy sweet foods without added calories or carbohydrates, but in amounts that won't take the place of other more nutritious foods that should make up the bulk of your diet.

Examples of a single serving include:
  • 8-oz diet soda (or other beverage)
  • 1/2 cup sugar-free pudding or gelatin dessert
  • 8 ounce container of sugar-free yogurt
  • One packet of artificial sweetener (added to any food or beverage)
It is one thing to sweeten your cup of tea in the morning with a little stevia. But in the United States, we live in a world of excess. We don't have one cup of tea; we have two or three, plus sweetened coffee, oatmeal, soda, smoothies and snacks, for example. Now that beverage companies have started using stevia, I can only assume that millions of people of all ages will consume large amounts of this sweetener throughout their lifetime. Just as I do with real sugar, natural sweeteners, sugar alcohols and sugar substitutes, I still preach moderation. It may sound boring, but it is the safest route to take.

Further Reading
The Truth about Stevia, the So-Called "Healthy" Alternative Sweetener by Natalie Digate Muth, M.D., M.P.H., R.D. for the American Council on Exercise (