Improving the quality of life for individuals with diabetes through optimal glycemic control is a major challenge. Polyphenols show great potential as adjuncts to current therapies in ameliorating metabolic disturbances. The C-glucosyl dihydrochalcone aspalathin, a polyphenol unique to rooibos (Aspalathus linearis) is poorly absorbed, with metabolites detectable in urine but not in plasma of mice (unpublished data), yet it displays antidiabetic (1,2), cardioprotective (3) and antimutagenic effects (4). In this study we demonstrated hypoglycaemic properties of an aspalathin-enriched green rooibos extract (GRE) in vivo, as well as propose the mechanism for intestinal transport, bioavailability and metabolism of aspalathin in vitro. Diet-induced pre-diabetic (PD) (n=8) vervet monkeys (Chlorocebus aethiops), together with normal controls (n=4) were treated with GRE (90mg/kg body weight) 3 x daily, with meals for 28 days. Intravenous glucose tolerance tests (IVGTT) were performed at base line (pre-treatment), during treatment (14 and 28 days) and after 28-day washout. The extract treatment significantly increased glucose tolerance as measured by decreased area under the curve in PD monkeys, after 14 (793.1±183.0 vs 524.8±103.1, p<0.01) and 28 (588.5±107.7, p<0.05) days returning nearly to normal (626.9±132.5) after washout. As expected, treatment showed no effect on normal controls. Following this positive effect on glucose tolerance, passage of aspalathin was monitored across CaCo2 cell monolayers in the presence and absence of inhibitors to expose mechanisms of transport and thus provide evidence for dose optimisation. Samples were analysed by HPLC-DAD and LC-MS, where aspalathin concentration was used to calculate Papp values (5) representing rate of transport. Aspalathin was transported at a rate typical of poorly absorbed compounds (1.59±1.08 x 10-6 cm/s2). Major glucose transporters, SGLT-1 and GLUT-2, were shown not to be primary transporters, nor was aspalathin effluxed into the gut lumen (1.9±0.85 x 10-6 cm/s2, efflux ratio: 1.2). The rate of transport was not affected by other polyphenols present in aspalathin-enriched extracts (1.6±0.75 x 10-6 cm/s2), but was affected by glucose concentration (2.9±0.76 x 10-7 cm/s2, p<0.05 at 20.5 mM glucose). Statistical significance was calculated using a student t-test, data is shown as mean ± SD. No metabolites were detectable in basolateral samples. Results confirm bioavailability of aspalathin, yet glucose lowering ability of extract in PD monkeys are significant. Mechanistically we showed that aspalathin was not actively transported by glucose transporters across Caco2 monolayers, but presumably passes paracellularly. To exploit bioactivity potential of aspalathin, further enquiry into delivery systems to increase aspalathin bioavailability are needed.