intestine-diagramThe stevia plant is indigenous to South America and originates from the sunflower family (Asteraceae). The sweet components within stevia leaves come from a group of compounds called steviol glycosides, which share a common steviol backbone. Carbohydrate residues (mainly glucose) are attached to the steviol backbone in various configurations to form the wide variety of sweet compounds found naturally in the stevia leaf. Steviol glycosides are poorly absorbed in the body and pass through the upper gastrointestinal tract, including the stomach and small intestines, fully intact. Once steviol glycosides reach the colon, gut bacteria hydrolyze steviol glycosides into steviol by snipping off their glucose units. Steviol is then absorbed via the portal vein and primarily metabolized by the liver forming steviol glucoronide, and then excreted in the urine.1 Research has shown that there is no accumulation of stevia (or any by-product of stevia) in the body during metabolism.2,3 It is a result of this essentially poor absorption in the digestive tract which ultimately contributes to the fact that stevia has zero calories and does not raise blood glucose or insulin levels when digested.

The chemical structure of steviol glycosides.

Stevia-Metabolism-Molecular-Structure-Image-De There are multiple steviol glycosides that have now been approved for use including those listed in the table below. Note the formulas and molecular weights vary, as does the conversion factor – this factor allows for the calculation of “steviol equivalents”. Notably, global regulatory agencies have created maximum use limits in their respective safety assessments which are expressed as steviol equivalents to account for the varying chemical structures of the steviol glycosides approved for use. Through the use of this conversion factor, the limits are adjusted accordingly to reflect the molecular weight of each given steviol glycoside.
Trivial nameFormulaMW (g/mol)Conversion factor X
SteviolC20H30O3318.451.00
SteviosideC38H60O18804.870.40
Rebaudioside AC44H70O23967.010.33
Rebaudioside CC44H70O22951.010.34
Dulcoside AC38H60O 17788.170.40
RubusosideC32H50O 13642.730.50
SteviolbiosideC32H50O13642.730.50
Rebaudioside DC50H80O28804.870.40
Rebaudioside EC44H70O23967.010.33
Rebaudioside FC43H68O22936.990.34
 

REFERENCES

  1. Gardana C, Simonetti, Canzi E et al. Metabolism of Stevioside and Rebaudioside A from Stevia Rebaudiana extracts by Human Microflora, J. Ag. Food Chem, 51(2):6618-6622, 2003.
  2. European Food Safety Authority, Panel on Food Additives and Nutrient Sources added to Food. Scientific opinion on the safety of steviol glycosides for the proposed uses as a food additive. EFSA Journal, 8(4):1537. 2010. [3. Biological and toxicological data (pg 20); 3.1. Absorption, distribution, metabolism and excretion (pg 20); 3.1.1. In vitro studies (pg 20);3.1.2. In vivo studies (pg 20)]. www.efsa.europa.eu/en/efsajournal/pub/1537.htm
  3. European Commission Regulation (EU) No 1131/2011 of 11 November 2011 amending Annex II to Regulation (EC) No 1333/2008 of the European Parliament and of the Council with regard to steviol glycosides. Official Journal of the European Union. December 11, 2011. Retrieved June 13, 2013: http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2011:295:0205:0211:EN:PDF