There is growing concern about the diabetes epidemic and the health of New Zealanders. While many therapies treat diabetes, far more important is prevention. We are participating in a large scale, long-term global programme, PREVIEW: Prevention of Diabetes through Lifestyle Intervention in Europe, New Zealand and Australia; recruiting 2500 overweight adults and children known to be at high risk. The study will test whether a higher protein diet is more successful for weight loss and diabetes prevention than current international best practice of a higher carbohydrate diet, and also the additional effect of moderate/higher exercise. This will be the first large international study to follow participants long term to discover who develops diabetes and who does not; what are the most important risk factors; and how can they best be modified through diet and exercise. This is a landmark study that will inform international diabetes recommendations.