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ORIGINAL RESEARCH ARTICLE

Metabolism of Stevioside by Healthy Subjects

Jan M. C. Geuns^*,1, Johan Buyse, Annelies Vankeirsbilck and Elisabeth H. M. Temme

^* Laboratory of Functional Biology, KULeuven, Kasteelpark Arenberg 31, B-3001 Leuven, Belgium; Faculty of Applied Bioscience and Engineering, Laboratory of Physiology and Immunology of Domestic Animals, Kasteelpark Arenberg 30, B-3001 Leuven, Belgium; and Faculty of Medicine, Department of Public Health, Division of Nutritional Epidemiology, Kapucijnenvoer 33-35, B-3000 Leuven, Belgium

To whom requests for reprints should be addressed at ¹ Laboratory of Functional Biology, KULeuven, Kasteelpark Arenberg 31, B 3001 Leuven, Belgium. E-mail: Jan. Geuns{at}bio.kuleuven.be

Stevioside (250-mg capsules) was given thrice daily for 3 days to 10 healthy subjects. Blood samples were collected and blood pressure measured after nocturnal fasting, before and at different time points during the third day of the administration of stevioside. No significant differences were found between the control and the stevioside condition for blood pressure and blood biochemical parameters. The 24-hr urinary volume and urinary excretion of electrolytes were not significantly different. Likewise, no significant difference was found for mean blood glucose and insulin between control and stevioside conditions. Thus, oral stevioside is not directly effective as a hypotensive or hypoglycemic agent in healthy subjects at the dose administered in this study.

Stevioside, free steviol, and steviol metabolites were analyzed in blood, feces, and urine after 3 days of stevioside administration. No uptake was found of stevioside by the gastrointestinal tract or the amounts taken up were very low and below the detection limit of the UV detector. Stomach juice did not degrade stevioside. All the stevioside reaching the colon was degraded by micro-organisms into steviol, the only metabolite found in feces. In blood plasma, no stevioside, no free steviol or other free steviol metabolites were found. However, steviol glucuronide (SV glu) was found in maximum concentrations of 33 µg/ml (21.3 µg steviol equivalents/ml). In urine, no stevioside or free steviol were present, but SV glu was found in amounts of up to 318 mg/24-hr urine (205 mg steviol equivalents/24 hrs). No other steviol derivatives were detected. In feces, besides free steviol, no other steviol metabolites or conjugates were detected. Steviol was excreted as SV glu in urine.

Key Words: Stevia rebaudiana (Bertoni) Bertoni (Asteraceae) • stevioside degradation • steviol • steviol glucuronide • mutagenic effects • toxicology