The leaves of the Stevia rebaudiana (Bertoni) plant contain sweet-tasting chemicals, which are extracted and purified to produce noncaloric artificial sweeteners. Stevia-derived products approved for use as sugar substitutes and tabletop sweeteners by the U.S. Food and Drug Administration contain the chemical rebaudioside A, or reb A, as the sole or principle ingredient. Rebaudioside A and related chemicals break down in your intestines into an absorbable molecule, which your liver detoxifies and your kidneys excrete.
Intestinal Breakdown
The metabolism of stevia can get confusing because the various chemicals involved in these processes have similar names. The sweet extracts from the stevia plant are collectively known as steviol glycosides. Rebaudioside A and stevioside are the most abundant of the steviol glycosides. The normal bacteria in your intestines gradually break down rebaudioside A and stevioside into the chemical steviol, which passes from your bowels into your bloodstream.
Liver Metabolism
The blood flow from your intestines travels directly to your liver. Your liver cells take up steviol and chemically join it to glucuronic acid in a detoxification process called conjugation. The conjugation of chemicals to glucuronic acid is a common detoxification mechanism used by your liver. Steviol glucuronide, the product of steviol conjugation in your liver, passes into your bloodstream and travels to your kidneys.
Kidney Excretion
Your kidneys filter steviol glucuronide from your blood and excrete it into your urine, which is the last step in ridding your body stevia-derived artificial sweeteners. Steviol glucuronide does not accumulate in your body, according to a review by the European Food Safety Authority.
Calorie Free
Stevia glycosides and their breakdown products do not enter the metabolic pathways that transform nutrients into energy. Because these pathways are bypassed, steviol glycosides contain no calories. However, some brands of stevia-derived artificial sweeteners contain other ingredients that may contain a small number of calories. If you are buying a stevia-derived sweetener, check the ingredients and nutrition facts to determine the product composition and calorie content.
Stevia vs. Stevia-Derived Sweeteners
Stevia and stevia-derived sweeteners are not the same thing. Whereas the sweeteners are highly purified extracts from stevia leaves, you can also purchase stevia as a nutritional supplement. The composition of stevia nutritional supplements may be more variable than the FDA-approved sweeteners.
GRAS
FDA-approved artificial sweeteners derived from the Stevia plant contain a high concentration of steviol glycosides. In approving these sweeteners, the FDA has deemed the products have met scientific standards to be "generally recognized as safe." Products must have a GRAS designation to be used as food additives in the United States.
References
- Calorie Control Council: Stevia/ Rebaudioside A
- U.S. Food and Drug Administration: What Refined Stevia Preparations Have Been Evaluated by FDA to be Used as a Sweetener?; June 2011
- University of California, Los Angeles; Toxicology Report of Rebaudioside A: A Review; Sarah Kobylewski, Ph.D., et al.; August 2008
- "European Food Safety Authority Journal"; Scientific Opinion on the Safety of Steviol Glycosides for the Proposed Uses as a Food Additive; F. Aguilar, et al.; April 2010
- U.S. Food and Drug Administration: Generally Recognized as Safe (GRAS)
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