Dose-dependent Effect of Grape Seed Extract on Glucose Control in People With Impaired Glucose Tolerance

The proposed study is a single-center, placebo-controlled, randomized, 4-arm, crossover study that identify the lowest effective dose of GSE on glucose control in people with impaired glucose tolerance. A planned sample size of 20 will be recruited into the study. This study will require one initial screening visit, pre-study visit, and 4 Oral Glucose Tolerance Test Days (OGTT) Days. This study will take 4-6weeks per subject to complete. The trial will initiate with one screening visit, which will last for about 3-4 hours where the subjects' height, weight, BMI, waist circumference, fasting blood glucose, blood pressure and heart rate will be measured and a survey related to general eating, health and exercise habits will be completed. OGTT procedure will be performed to confirm IGT. If willing and eligible to participate, a 3-day food record (2 weekdays and 1 weekend) will be given at the screening visit and collected on the following pre-study Visit to assess subject's baseline dietary intake and pattern. Also, subjects will be instructed to follow a relatively low polyphenolic-diet at least 7 days prior to the first OGTT Day and for the duration of the study. A dinner meal will be provided the day before the OGTT Day to control the second meal effect from food and beverage intake of the night before the OGTT Day. Subjects will arrive at the center in a fasting state for at least 10 hours, well hydrated and rested. Each OGTT Day will require blood draws throughout the visit. After evaluation of subject's health status (via anthropometric, vital sign and blood glucose measurements and in-person interview), a registered nurse will place a catheter in subject's arm for the purpose of multiple blood sample collections and take the initial blood draw (baseline: -1h) in the fasting state. 3 test capsules with 0 mg GSE, 300 mg GSE, 600 mg GSE or 900 mg GSE (in forms of: 3 placebo, 2 placebo \& 1 GSE, 1 placebo \& 2 GSE or 3 GSE. Each GSE capsule containing 300 mg GSE) will be served. Thereafter, timers will be started and a glucose test drink (75g glucose mixed with 250ml water) will be given right after the 0h blood sampling (1 h after the consumption of capsules). Subject will be instructed to finish the drink in 5 minutes (min). From this point forward, blood sample will be collected at 30 min, 1h, 2hand 3h for assessment of changes in metabolic markers. The sequence of receiving the capsules treatment at each visit will be randomly assigned based on computer generated sequences. OGTT Day visits will be placed at least 3 days apart as well.