Stevia (STEE-vee-uh) is one of six non-nutritive sweeteners – the only natural non-nutritive sweetener – approved by the FDA. The name stevia is derived from an herb, the stevia rebaudiana shrub native to Paraguay and Brazil. Out of the six approved non-nutritive sweeteners – the others being saccharin, aspartame, acesulfame potassium, sucralose, and neotame – stevia is the newest, with highly refined extracts gaining generally recognized as safe (GRAS) status in December of 2008.
Stevia extract comes from the stevia genus, which includes about 240 species of herbs and shrubs from the sunflower family (Asteraceae) native to tropical and semi-tropical areas of the Americas.  It originally grew in the mountainous areas (Amambay Mountain region) of Paraguay and Brazil. The Guarani Indians – based in South America, including Paraguay – called one species that sweetened kaa-he-he, translating to “sweet herb”, using it to enhance the taste of bitter mate (a tea-like beverage) and medicinal potions for centuries.  It is now said that the leaf by itself is 30 to 45 times sweeter than sucrose (table sugar). “The Spanish Conquistadors of South America learned about Stevia’s properties from the Guarani and Mato Grosso Indian tribes in the early 1500s.”  Introduced to settlers of the region by the 1800s, daily stevia consumption was normal in not just Paraguay, but also in neighboring Brazil and Argentina.  Dr. Moises Santiago Bertoni, a Swiss botanist, first discovered the plant in 1887 thinking it was a new species and, 12 years later, announced the “discovery”. In 1906, bertoni would name the species in honor of the Paraguayan chemist Dr. Rebaudi (Stevia rebaudiana), who later became the first to extract the plant’s sweet component.  This would be the start of Stevia rebaudiana as a commercially known sweetener that could be grown and cultivated elsewhere.
This history lets us know that stevia has been around for centuries, unlike artificial sweeteners, and is probably the most extensively tested and used sweetener because of it. Like all life, plants are trying to survive, which usually means they adapted and evolved to ward off animals, as well as you and me, from eating it. This is one important reason to question its safety, but there’s a lot of safe usage shown through its history.
“In 1991, the U.S. Food and Drug Administration (FDA) labeled Stevia as an unsafe food additive and restricted its import. In 1995, the FDA allowed Stevia to be used as a dietary supplement, but not as a food additive. In 2008, the FDA approved use of rebaudioside compounds derived from the Stevia plant developed by Coca-Cola and PepsiCo.”  Stevia is still not allowed in U.S. meat or poultry, but in any other food and beverage as of its GRAS status. [8 – PDF] Stevia has been permitted as a food additive in the European Union as of December 2nd, 2011. 
For a visual representation of Stevia’s 20th century history, view here. (PDF)
What Makes It Sweet?
Through the approximate 240 varying species of Stevia we now know the one that sweetens is Stevia rebaudiana. Chemically, this species differs from the others because it contains something called steviol glycosides. Assuming most readers are not botanists or chemists, the important thing to know is that there are different glycosides in the plant, and they do matter. The glycosides consist of stevioside, steviolbioside, rebaudioside (A, B, C, D, E, F), rubusoside and dulcoside A. [5 – PDF] “They are isolated and purified from the leaves of the stevia plant, where it is present at levels up to 13%.” Out of the 13% of the plant that contains the steviol glycosides the two most important ones, and the ones that are most present in the plant, are stevioside (5-10%) and rebaudioside A (2-4%).
As a sweetener, “the most important glycoside is rebaudioside-A, which has the advantage over most other high intensity sweeteners of being heat and acid stable, allowing it to be used in acidic fruit juices and pasteurised dairy products.”  It also is the best tasting glycoside from the Stevia rebaudiana plant. Rebaudioside A is the extract that was first allowed as a food sweetener by the FDA in 2008, needing to be purified upwards of 95%+ of a product to be accepted. Now, regulations are slightly looser and accepted purified versions of Stevia must include a 95%+ mix of stevioside and rebaudioside A, although much of the marketplace contains products mostly of rebaudioside A. 
Stevioside is listed as 250 to 300 times sweeter than sucrose, but slightly bitter, in its pure form while rebaudioside A is listed as 350 to 450 times sweeter than sucrose, and not as bitter, in its pure form. The bitterness is considered to have a licorice taste, and has led producers to keep some sugar in their products to maintain a desired taste.  There are many brands and combinations of Stevia extract that may appeal to consumers differently.
What Does The Research Say?
Although Stevia has been used for centuries and is a natural product, we know that doesn’t mean it’s necessarily safe, even if some people think so. Research for the refined versions of Stevia have been carried out like any other food additive on the marketplace. Gaining GRAS status by the FDA “means [is] that high purity rebaudioside A […] has been studied extensively and the FDA has found the studies to be acceptable and convincing to established scientists in proving no significant harm.” The FDA also issued a letter of no objection to two large food and beverage companies (Coca Cola & PepsiCo), which ” is a letter sent to the applicant that states that all of the extensive clinical data generated on the effects of high purity rebaudioside A shows no potential for harm to humans at the suggested dose.”  The European Food Safety Authority (EFSA), has a scientific opinion on the safety of steviol glycosides, which established an ADI (Acceptable Daily Intake) of 4 mg/kg of bodyweight/day. To put the ADI into perspective, “a 150-pound person would need to consume approximately 30 packets of a tabletop stevia sweetener.”  Also in the EFSA article, “the Panel concludes that steviol glycosides, complying with JECFA specifications, are not carcinogenic, genotoxic or associated with any reproductive/developmental toxicity.”
One issue brought up about Stevia is what could be considered overuse of the product. Since the natives of Paraguay probably didn’t binge on leaves, the worry is that commercial use of the product, especially since it is heat stable and can be used as a full sugar replacement, may lead to over consumption by consumers. However a study by the JECFA may help reassure that the ADI, which is the value considered safe in animals divided by 100, may not easily be achieved regardless. “JECFA assumed that steviol glycosides would replace all dietary sugars, at the lowest reported relative sweetness ratio for steviol glycosides and sucrose which is 200:1 . The intakes ranged from 1.3 mg/kg bw/day with the African diet to 3.5 mg/kg bw/day with the European diet.” [6 – PDF] This means even fully replacing the average persons intake of sugar with stevia would still not reach the listed ADI in most situations.
Here is a chart on the amount of stevia needed to replace certain amounts of sugar, such as when you cook:
What do I think?
Stevia looks to be a safe alternative to sugar, but that doesn’t mean I would outright recommend it or that I will switch to using it. I do believe a diet full of sugar would be better off being a diet full of stevia, but neither seems to be the smartest choice. If you can’t give up sugar no matter what, Stevia will probably be your best bet. If you suffer any side effects that you can trace to your usage of Stevia, then you’re probably in the minority but it’s worth stopping the use of the product immediately. Like any plant or vegetable, not everyone will react the same way to its use, but no studies can prove any permanent harm or health hazards from using Stevia products. That said, if you’re a diabetic currently using artificial sweeteners a switch to Stevia may be a smart choice. However, if you’re diabetic and you don’t use any non-nutritive sweetener in your diet (meaning you’ve gotten over any past sugar cravings) I would stay away from Stevia, as it may lead to more sweetness cravings.
Further more, if you end up buying products made with Stevia you may have a bigger problem on your hands. Anything that has a non-nutritive sweetener in it is probably processed food, and from a health standpoint most processed food can, and are, harmful to your health by looking at other studies. Stevia may be a helpful sign that your diet could contain more real whole foods and less processed foods.
My diet is so low in sugar I will probably never use Stevia, but if you feel you could limit your sugar and want to bake a cake this weekend, knock yourself out and replace the sugar with Stevia and see how it goes and if it ruins the taste for you. After researching all 6 FDA-approved non-nutritive sweeteners Stevia is the only one I feel comfortable recommending to my friends, family, and general consumers.
One cool fact about Stevia is that it can be grown in our own gardens, and is suitable for most climates! Although it may not be a profitable journey it may be a fun addition to your garden. Check here if you’re interested.
What are some common and trade names for stevia sweeteners? [8 – PDF]
Reb A Rebaudioside A
Stevioside Stevia Extract In The Raw™
Sun Crystals® Truvia™
Rebiana is the trade name for a zero-calorie sweetener containing mainly rebaudioside A (also called Reb A).
Enliten is Corn Products International‘s brand of Reb A sweetener.