Determining the relationship between dietary carbohydrate intake and insulin resistance

Insulin resistance underlies type 2 diabetes, CVD and the metabolic syndrome, driven by changes in diet, lifestyle, energy over-consumption and obesity. Nutritional recommendations for insulin resistance remain an area of controversy, particularly the quantity and types of dietary carbohydrate. The present review gives an overview of insulin resistance, its relationship to impaired insulin secretion and the metabolic syndrome, research methodologies used to measure insulin action and the epidemiological and intervention studies on the relationship between dietary carbohydrate and insulin resistance. Epidemiological studies provide little evidence to suggest that total dietary carbohydrate predicts risk of type 2 diabetes, and high-carbohydrate, high-fibre diets with low-glycaemic index (GI) may even contribute to diabetes prevention. Despite inherent limitations associated with techniques used to measure insulin resistance and dietary assessment, most intervention studies reveal an increase in glucose tolerance or insulin sensitivity with high-carbohydrate, low-fat diets in non-diabetic and diabetic individuals. When energy is restricted the source or reduced content of carbohydrate does not appear to be as important as fat for body weight. Thus, low energy intake is key to weight loss and augmentation of insulin sensitivity. Given this, widespread adoption of popular low-carbohydrate high-fat diets highlights the necessity to evaluate dietary interventions regarding safety and metabolic effects. While current evidence supports FAO/WHO recommendations to maintain a high-carbohydrate diet with low-GI foods, the relationships between carbohydrate and insulin sensitivity remains an important research area. Emerging technologies should further enhance understanding of gene-diet interactions in insulin resistance, providing useful information for future nutrition policy decisions.