Optimal macronutrient balance

There is at present a justifiable debate as to the optimum level of total d ietary fat which will reduce the risk of obesity without an elevation of pl asma triacylglycerol or a depression of plasma HDL-cholesterol. Total plasm a cholesterol and LDL-cholesterol levels are lowered and risk of fatal myoc ardial infarction is lowered when either saturated or trans-unsaturated fat ty acids are replaced isoenergetically by either monounsaturated or polyuns aturated fatty acids. The triacylglycerol-raising and HDL-lowering effects of low-fat high-carbohydrate diets can be overcome with low intakes of n-3 polyunsaturated fatty acids and moderate exercise. Whilst a reduction in di etary fat is being attained in many countries, the reduction is uniform acr oss all fatty acids, leaving dietary fat composition unchanged. The ability of low-fat diets to reduce cholesterol and cause a fall in body weight is not influenced by the carbohydrate ratio starch:sugars in the diet. However , weight-gain susceptibility to high intakes of dietary fat and the plasma cholesterol responsiveness to diet are considerably influenced by common ge netic polymorphisms.