Carbohydrates, fat, and insulin action.

Insulin resistance is a common disorder and is seen in many conditions that are associated with increased risk for cardiovascular disease (eg, obesity, diabetes, hypertension, and cigarette smoking). The role of the diet, irrespective of degree of obesity, in modulating insulin sensitivity is uncertain. An extremely high carbohydrate-fat ratio improves insulin sensitivity whereas more moderate changes (40-60% carbohydrate) produce less convincing results. However, increased fasting concentrations of triglycerides and lower concentrations of high-density-lipoprotein (HDL) cholesterol have frequently been seen with these diets, together with lower concentrations of low-density-lipoprotein (LDL) cholesterol. High-carbohydrate diets based on foods with a low glycemic index combined with a high dietary fiber content should be evaluated. Such diets may produce the desired effects while they prevent unwanted increases in fasting triglyceride concentrations and lower HDL cholesterol.