Can we out-run the diabetes epidemic?

According to the WHO, the worldwide prevalence of diabetes in 2030 is expected have doubled from the year 2000 estimate of 171 million [1]: by all estimates, the prevalence of type 2 diabetes has already reached epidemic proportions in the developed world. Observational studies have demonstrated that, with few exceptions, overweight and obesity are almost ubiquitous in type 2 diabetes, and the relatively large projected growth in the prevalence of diabetes in the developing world is largely attributable to the spread of overweight and obesity. Intervention programmes to prevent the development of diabetes should therefore focus on reversing overweight and obesity, which underlie this devastating disease. When the findings from the Diabetes Prevention Program (DPP) were first announced in 2002 [2], the scientific community was not surprised to learn that study participants in the intensive lifestyle intervention arm had a lower risk of developing diabetes than their counterparts in the placebo arm. The surprising finding was that intensive lifestyle intervention, based on dietary energy restriction and encouragement to engage in moderate physical activity on most days of the week, with a goal of achieving 7% weight loss [3], performed better than metformin in preventing high-risk participants from developing diabetes. Later evidence that the intensive lifestyle intervention was a cost-effective alternative to pharmacological therapy [4] reemphasised the benefits of diet and exercise in the prevention of diabetes. If lifestyle intervention is such a resounding success, why is it important to determine whether it is diet or physical activity that is driving the success? The answer to that question lies in the difficulty individuals have in adopting lifestyle changes. Compliance with lifestyle intervention certainly varies between individuals, but inter-individual variability in the physiological responses to diet and exercise is even greater. By simplifying interventions to focus on the most effective component, or the component that is easiest to adopt (as the two are not often the same), we might improve compliance with the intervention and thus achieve greater success in preventing disease. In this issue of Diabetologia, Yates et al. [5] report on a systematic review of clinical trials to determine whether the physical activity component of lifestyle interventions prevents the development of diabetes or lowers fasting or 2-h blood glucose levels in participants with impaired fasting glucose or impaired glucose tolerance. The stated goal of the review is to determine whether physical activity demonstrates a protective association with incident diabetes, independently of dietary energy restriction. The authors summarise the findings from eight controlled trials and report that lifestyle interventions reduced the incidence of diabetes by approximately 50%, but that there was little decrease in blood glucose during the intervention period. None of the studies could determine whether the reduction in risk was independent of weight loss. Based on these results, Yates and colleagues conclude that the evidence for exercise interventions in preventing the development of diabetes is equivocal. Further, the authors advance the hypothesis that the reduction in diabetes incidence is probably attributable to factors other than increased physical activity since, when measured, actual changes in physical activity were minimal. Diabetologia (2007) 50:1113–1115 DOI 10.1007/s00125-007-0673-5