This thesis begins with a background chapter which explores the current diabetes epidemic and examines the role of obesity and oxidative stress as causative factors. Current dietary recommendations for prevention of type 2 diabetes are critically evaluated. A systematic review and meta-analysis was conducted to determine the independent role of fruit and vegetables in preventing diabetes. Convincing benefit for greater consumption of green leafy vegetables was demonstrated. An insignificant trend towards benefit was observed for fruit and vegetables. The Fruit and Vegetable Intake and Glucose Control Study (FIVE) is a sub study of the Let’s Prevent Diabetes Study. FIVE includes cross sectional analysis of baseline plasma vitamin C, (a biomarker for fruit and vegetable intake) from 2101 participants. FIVE further includes 12 months analysis of individuals with impaired glucose regulation, randomised to receive group education or usual care. Results demonstrate 29% of the population consumed at least 5 portions of fruit and vegetables a day. Fewer South Asian individuals met the recommendation compared to White Europeans (21% vs. 30% p = 0.003). Each additional piece of fruit or vegetable consumed (21.8μmol/l plasma vitamin C) was associated with a reduction of 0.04% in HbA1c, 0.05mmol/l in fasting and 0.22mol/l in 2 hour blood glucose. Participants who consumed 5 portions a day compared to those who did not, had a 24% associated reduced risk of being diagnosed with impaired glucose regulation (OR = 0.76, 95% CI: 0.59 to 0.98). At 12 months follow up those receiving lifestyle education had greater levels of plasma vitamin C compared to those in the usual care arm (36.1μmol/l (SD 20.7) vs.29.9μmol/l (SD 20.3)). No statistical difference in mean change between intervention arms was seen. The thesis provides novel, robust nutritional biomarker data from a large at risk, multi ethnic population. Results support recommendations to promote fruit and vegetables in the diet to prevent diabetes. The potential for tailored advice on increasing green leafy vegetables among those at risk of diabetes should be investigated further.