By Mauro Fisberg, MD, PHD, Scientific Advisory Board Member, Global Stevia Institute
Stevia’s sweet compounds, including stevioside and rebaudioside A (common name Reb A), are diterpene glycosides (ent-13-hydroxykaur-16-en-19-oic acid) extracted from the plant Stevia rebaudiana Bertoni native to Paraguay and Brazil.1,2 Due to its intense sweetening capacity (up to 400 times sweeter than sugar) and the fact that it is a non-caloric ingredient with superior solubility in water and a positive taste profile, stevia sweeteners have been used for more than 40 years in Japan and are now becoming more widely used in the food and beverage industry in Asian countries as well as in North and South America.1,3
The metabolism and elimination of stevia has been studied in both animals and humans.4,5,6 These studies conclude that stevia is safe for use as a general sweetener in the food supply. Here is a brief overview of stevia metabolism.
The major steviol glycosides are metabolized through similar pathways. Reb A is first metabolized by microbes in the colon to stevioside and then releases a glucose molecule as it is converted to steviol. The released glucose molecule is used by the bacteria in the colon and is not absorbed. Since the steviol glycosides are metabolized to steviol this means that the metabolic equivalency of the different steviol glycosides permits us to apply the findings from studies with stevioside to the safety evaluation of Reb A, and thus to the safety of stevia, in general.2 These conclusions have been verified by numerous animal and human studies.
While there are some differences between species, it has been demonstrated that the conversion rate of Reb A and stevioside are similar between rats and humans, with the conversion from stevioside to steviol more rapid than that of Reb A to stevioside in both species. Moreover, quantitative and qualitative similarities have been found between the organisms in the gut (microflora) of the rat and the human body.7 In addition, the toxicity of stevia has been investigated extensively in both short- and long-term studies. Importantly, no serious toxic, genotoxic, or carcinogenic effects were detected in mammalian species.8,9
Despite previous reports that steviol is further broken down (i.e. steviol to hydrosteviol or dihydroxysteviol)10,11, 12 a study on the human digestive tract demonstrates that steviol is not altered or changed at either high or low concentrations as observed through human feces, indicating that steviol is in fact the final product of stevia metabolism.2 The study also showed that the majority of these steviol glycosides are absorbed and glucuronidated (a bond intended to help them clear out of the blood) in the liver. The newly bonded glucuronide is released in the blood and filtered by the kidneys into the urine. Small amounts of glucuronidate that remain in the colon are excreted through fecal matter.
- Intake/output studies demonstrate that it is excreted thoroughly without any residual stevia in the body; there is no accumulation in the kidneys or the liver7
- There is no calorie yield by the body
- Stevia has no effect on the body aside from the sweetening taste it offers
- Stevia does not cause any gastrointestinal disturbances or stomach upset as is common with many sugar alcohols
Stevia is stable in food and beverage systems, so it is unlikely that other metabolites – or breakdown to new compounds – would occur. It has been previously reported that no degradation products were indentified in tabletop powder at conditions up to 105ºC for 96 hours.13 Additionally, no significant degradation was seen over a 25-week period of simulated diet soft drink condition (i.e., pH 3.0, ambient temperature around 70ºF, refrigeration around 40ºF, in an aqueous citric acid matrix). 13
Taken together, the research indicates that stevia is safely metabolized by the body without any effect.
1 Geuns JM. Stevioside. Phytochemistry. 2003; 64(5): p. 913-21.
2 Koyama E, et al. In vitro metabolism of the glycosidic sweeteners, stevia mixture and enzymatically modified stevia in human intestinal microflora. Food Chem Toxicol. 2003; 41(3): p. 359-74.
3 Soejarto DD, et al. Potential sweetening agents of plant origin. III. Organoleptic evaluation of Stevia leaf herbarium samples for sweetness. J Nat Prod. 1982; 45(5): p. 590-99.
4 Geuns JM, et al. Metabolism of stevioside in pigs and intestinal absorption characteristics of stevioside, rebaudioside A and steviol. Food Chem Toxicol. 2003; 41(11): p. 1599-607.
5 Geuns JM, et al. Metabolism of stevioside by healthy subjects. Exp Biol Med (Maywood). 2007; 232(1): p. 164-73.
6 Geuns JM, et al. Metabolism of stevioside by chickens. J Agric Food Chem. 2003; 51(4): p. 1095-101.
7 Wingard RE, et al. Intestinal degradation and absorption of the glycosidic sweeteners stevioside and rebaudioside A. Experientia. 1980; 36(5): p. 519-20.
8 Aze Y, et al. Subchronic oral toxicity study of stevioside in F344 rats. Eisei Shikenjo Hokoku. 1991; 109: p. 48-54.
9 Toyoda K, et al. Assessment of the carcinogenicity of stevioside in F344 rats. Food Chem Toxicol. 1997; 35(6): p. 597-603.
10 Compadre CM, et al. Mass spectral analysis of some derivatives and in vitro metabolites of steviol, the aglycone of the natural sweeteners, stevioside, rebaudioside A, and rubusoside. Biomed Environ Mass Spectrom. 1988; 15(4): p. 211-22.
11Hutapea A, et al. Digestion of stevioside, a natural sweetener, by various digestive enzymes. Journal of Clinical Biochemistry and Nutrition. 1997; 23: p. 177-186.
12 Pezzuto JM, et al. Metabolically activated steviol, the aglycone of stevioside, is mutagenic. Proc Natl Acad Sci USA. 1985; 82(8): p. 2478-82.
13 Purkayastha S. Stevia – a natural beverage for the market. Australian Beverages Council: Yearbook 2009; pp. 35-39.