The effect of exercise and diet on glucose intolerance and substrate utilization?

Intervention studies provide robust evidence of the efficacy of lifestyle intervention, based on diet and exercise, in improving insulin sensitivity and reducing the risk of developing type-2 diabetes in individuals with impaired glucose tolerance (IGT) [1–3]. However, it is difficult to determine the relative importance of weight loss compared with physical activity in improving clinical outcomes. A prospective study in 5,159 men without diabetes at baseline demonstrated a strong inverse relationship between physical activity and the risk of developing type-2 diabetes (table 1), suggesting a beneficial effect of physical fitness on glucose tolerance and insulin sensitivity [4]. Indeed, the prognostic benefits associated with physical activity remained after adjustment for potential confounders, including factors related to lifestyle, body mass index (BMI) and preexisting disease. A further study, which enrolled 8,633 non-diabetic subjects, examined the association of cardiorespiratory fitness, an objective marker of physical activity, with the development of impaired fasting glucose (IFG) which, like IGT, represents a pre-diabetic state, or type-2 diabetes [5]. During an average follow-up of 6 years 593 subjects developed IFG and 149 subjects developed type-2 diabetes. After adjustment for age, smoking, alcohol consumption and family history of diabetes, it was determined that low cardiorespiratory fitness was independently associated with an increased risk of developing IFG and type-2 diabetes. Allison SP, Go VLW (eds): Metabolic Issues of Clinical Nutrition. Nestlé Nutrition Workshop Series Clinical & Performance Program, vol 9, pp 93–109, Nestec Ltd., Vevey/S. Karger AG, Basel, © 2004.