Insulin resistance: concepts, controversies, and the role of nutrition

Insulin resistance is a prevalent condition, in which insulin loses its normal physiological action. Since people were first classified as insulin resistant over 60 years ago, one of the main discoveries has been that insulin resistance clusters with other risk factors such as obesity, elevated triglycerides, and low high-density lipoprotein cholesterol, increasing cardiovascular disease risk. Although insulin resistance appears to manifest first in the periphery and then in the liver, other sites, such as the brain and the pancreatic &b.beta-cell, may play pathogenic roles. Factors contributing to insulin resistance at these sites include perturbations in free fatty acids, glucose, and hormone-signalling, some of which may be linked to various genetic polymorphisms. Appropriate nutritional treatment for insulin resistance is controversial. Two main approaches are drawn from diabetes recommendations: i) a high-carbohydrate, low-fat, high-fibre diet emphasizing low glycemic-index foods and ii) sharing calories between monounsaturated fat and complex carbohydrate at the expense of saturated fat. Recent interest in insulin resistance has prompted the development of new guidelines. Promising data have also emerged, showing that a high-carbohydrate, high-fibre, low-fat diet plus exercise programs maintained through intensive counselling can decrease diabetes risk by over 40%. Additional research is required to confirm the sustainability of this approach and sort out the determinants of insulin resistance so that more effective nutritional interventions will result.