The GLARE (Glucose Lowering Antioxidant-Rich Food Extracts) Study: Can Antioxidant-Rich food extracts reduce your risk of diabetes?

The acute effect of four antioxidant-rich food extracts on postprandial blood glucose and insulin response in people with prediabetes will be investigated. The following four antioxidant-rich products will be tested in this study: Amla berry extract (Sharman Ltd, Nelson, New Zealand); Grape seed extract (NutraLife, New Zealand Ltd),; Rooibos tea extract (Rooibos Ltd, Clanwilliam, South Africa) and Olive Leaf Extract (COMVITA, NZ) Dose: For this study we will have 2.0 times the total antioxidant capacity (i.e approx 640 mg) as was performed in Chepulis et al. (2016) study. Antioxidant activity (as determined by ORAC assay) of each product used in this study, will be measured by Callaghan Innovation (Wellington, New Zealand. For the purposes of comparison a vitamin E sample (with a known effective concentration half-life (EC50) of 0.44 mg/mL) is included. EC50 values of the tests samples will be calculated as mg/mL. Each test sample will have equivalent total antioxidant activity and on a weight per weight basis the number of capsules (for 2x antioxidant capacity) consumed by the participant orally before the OGTT will be determined once antioxidant activity for the product has been assessed. The test session will include: An OGTT with placebo control capsule or antioxidant-rich food extract capsule administered 10 minutes before the glucose drink (75 g glucose in 200 mL water). Participants will be cannulated and observed over a 2 hour period with blood samples taken at T=0, 15, 45, 60, 90, and 120 minutes. The participant will be fasted (approx 10 hrs) before starting test session. A researcher and assistant will be present throughout the OGTT. All participants (recruitment of 20) will undergo 5 test sessions (placebo control and 4 antioxidant-rich food extracts. There will be a minimum of 48 hrs washout period between each test session. The full testing should take between 8-10 weeks. Between Test Sessions: All participants will be asked to keep their diet and lifestyles as constant as possible throughout the study and to refrain from engaging in any strenuous physical activity (walking is fine) or consumption of alcohol in the 24-hour period prior to each test session. Participants will also be asked to avoid the active test foods/extracts for at least seven days prior to the first test session and throughout the duration of the test period (including avoiding other teas and formulations where the extracts may be present. A list of such foods/teas and formulations will be provided to participants). Chepulis, L., Al-Aubaidy, H., Page, R. (2016) Effect of selected antioxidant food extracts on postprandial glucose responses in healthy individuals. Functional Foods in Health and Disease, 6(8): 493-505