Purpose of reviewThis review assesses the relative effect of fat versus carbohydrate and the differences between fatty acids and types of carbohydrate on insulin resistance and associated risk factors for diabetes and cardiovascular disease.Recent findingsThe debate continues over whether high-carbohydrate or high-fat diets have the more deleterious metabolic effects. Large randomized controlled trials have shown that a reduction of fat intake as part of a healthy lifestyle combined with weight reduction and exercise reduce the risk of type 2 diabetes. Carbohydrate as fruit and vegetable together with low-fat dairy products reduce blood pressure. The results of trials of fatty acid type continue to favor the use of monounsaturated fats. However, the advantages over carbohydrate have not always been clear. In terms of carbohydrate, the glycemic index appears to be a better predictor of the metabolic effects of a diet than the sugar content. The fiber content of the carbohydrate food appears to confer benefits in terms of diabetic control. Lower cholesterol and postprandial blood glucose results are associated with viscous fibers.SummaryDiets that are higher in monounsaturated fatty acids, fiber and low glycemic index foods appear to have advantages in insulin resistance, glycemic control and blood lipids in a number of studies. The division of nutrients into total fat (regardless of fatty acids) versus carbohydrate (type and quantity not specified) appears to be less helpful in predicting outcomes.