Stevia is a widely used, very potent sweetener, but few herbals have sparked as much controversy.
Also known as sweet leaf, Stevia rebaudiana is a perennial shrub with more than 150 species that is native to Paraguay. The leaves are so intensely flavored that Paraguayans have been using the herb as a sweetening agent for centuries.1,2

But regardless of this lengthy history in South America, stevia has met with intense resistance in the United States. The FDA banned the herb in 1991, citing what it called a lack of demonstrated safety. After years of public outcry, the FDA allowed stevia to be used as a dietary supplement but not as a food additive.

The prohibition still stands, despite stevia’s popularity in most European and Asian countries. For example, Japan has been cultivating stevia and producing stevia sweeteners since 1977.2

Background

Stevia’s flavor is very concentrated, with 250-300 times the sweetness of a 0.4% solution of traditional table sugar.3 The taste is slightly different from traditional cane sugars. Much like maple syrup and honey, it has a characteristic flavor that, though sweet, is unique.4

Cooking with stevia often requires some recipe alterations. Adding it to fresh fruit or dairy foods is usually fine, but baking can present a problem. Unlike traditional cane sugar, stevia can’t enhance texture, caramelize, feed yeast fermentation, or tenderize batter. Texturizing ingredients — such as canned pumpkin or mashed banana — and extra leavening agents are often needed to produce an acceptable baked product.2

The Coca-Cola Company and Cargill Foods have a patent pending for Rebiana, a zero-calorie nonsugar sweetener derived from stevia. They are awaiting regulatory approval to use it in various food products.2

Mechanism of action

Stevia has been shown to have benefits beyond sweet flavor, particularly for people who have diabetes or hypertension. Some data suggest that the glycosides stevioside and rebaudioside A may increase insulin production.2 Stevia delays glucose absorption from the intestine and possibly improves cellular-level insulin sensitivity. There is also evidence that the herb actually lowers blood-sugar levels in diabetics by improving carbohydrate metabolism and increasing insulin production.3

Stevia seems to have a mild vasodilatory effect, probably by altering calcium and/or potassium in the arteries.3 This is usually considered beneficial because it can increase renal flow.1

The herb can also help with hypertension. For example, in a two-year placebo-controlled trial involving 106 participants, those who used stevia three times a day saw an average BP reduction from 166/102 mm Hg to 153/90, while no significant change was observed among those on placebo.5

Safety

The FDA’s concerns include reproductive toxicity and carcinogenic potential.6 However, numerous studies in both animals and humans have failed to substantiate these fears, and there are no known harmful effects on people.2

In 2006, the World Health Organization (WHO) evaluated all recent experimental data on stevia. It concluded that “stevioside and rebaudioside A are not genotoxic in vitro or  in vivo” and that “stevioside has shown some evidence of pharmacologic effects in patients with hypertension or with type 2 diabetes.”1

Study summaries published in the journal Phytochemistry confirmed that there were absolutely no indications of fertility impairment or teratogenicity from stevia. Metabolic effects were, if anything, positive, and people with such dietary impairments as phenylketonuria were able to use the herb.3

The best carcinogenic studies are longitudinal and take years, but early data do not indicate a problem. In fact, the opposite is true. A study by Japanese researchers actually showed a tumor inhibitory effect on cancers in mice.7

Stevia is also the object of scrutiny among dentists. Early studies indicate that because it is a non-glucose-based sweetener, tooth decay and dental caries formation may be reduced with the continued use of stevia products.2 Since tooth decay and gum disease have been strongly linked to such conditions as heart disease, this finding could have major implications for general wellness and health promotion across the population.
Another safety concern seems to stem from the fact that stevia is a glycoside, a family of chemicals that can have direct effects on the heart. However, tests to date have not shown any cardiac impact.3

All current data indicate that stevia is safe as an alternative sweetener, but people on medication regimens, particularly diabetics and hypertensives, should consult their health-care providers about possible changes to their prescriptions.

Supply and cost

Stevia is sold as a concentrated liquid or powder, in shaker bottles, individual packets, or multi-use bottles. Most sources price it at about $6 for a 50-use package, whether as a powder or extract.
Plants can sometimes be grown domestically from seeds or seedlings.

Summary

There appears to be no significant solid evidence to support the FDA’s reluctance to approve stevia products in foods. No current sweetener is without health-related controversy, and all sugar substitutes should be examined before they receive FDA approval and become widely used. How-ever, given what we already know to be the pitfalls of our massive use of traditional table sugar and high-fructose corn syrup, it would seem that we have only our pounds and diabetes to lose by expanding our choice of alternative sweeteners with this herb.

References
1. Geuns JMC. Stevioside. Phytochemistry. 2003;64:913-921.
2. University of Nebraska-Lincoln Extension. Institute of Agriculture and Natural Resources. Stevia. Available at
www.ianrpubs.unl.edu/epublic/pages/publicationD.jsp?publicationId=609. Accessed September 21, 2008.
3. Drug Digest. Stevia. Available at www.drugdigest.org/DD/DVH/HerbsWho/0,3923,552027%7CStevia,00.html. Accessed September 21, 2008.
4. Smith J. Stevia: a new player in the artificial sweetener game. Diabetes Health. 2006.
5. Agriculture Information. Medicinal properties of stevia. Available at www.agricultureinformation.com/forums/stevia/8089-medical-properties-stevia.html. Accessed September 21, 2008.
6. Schardt D. Stevia: a bittersweet tale. Nutrition Action Health Letter. April 2000. Available at cspinet.org/nah/4_00/stevia.html. Accessed September 21, 2008.
7. Yasukawa K, Kitanaka S, Seo S. Inhibitory effect of stevioside on tumor promotion by 12-O-tetradecanoylphorbol-13-acetate in two-stage carcinogenesis in mouse skin. Biol Pharma Bull. 2002;25:1488.