Purpose of reviewTo evaluate the evidence with regard to high-versus low-fat diets in the context of the prevention and management of obesity, type 2 diabetes and coronary heart disease.Recent findingsDespite the increasing prevalence of obesity, there is no evidence to support the view that this is caused by an increased intake of fat. Fat sensors play an important role in regulating energy balance and lipid metabolism, and hypoenergetic diets containing 30-35% energy from fat promote weight loss. High intakes of carbohydrates with a high glycaemic index can result in insulin resistance, but this effect can be modulated by increased physical activity.SummaryAlthough arguments to decrease the intake of trans and saturated fatty acids are cogent, the scientific basis for a reduction in the proportion of energy from fat below 30% energy is not supported by experimental evidence. A modest reduction in fat intake to 30-35% energy, with the bulk of carbohydrates being derived from complex carbohydrates from unrefined sources, would appear to be the best option for the prevention of obesity and cardiovascular disease. Increased physical activity appears to be particularly important in modulating the adverse effects associated with high-carbohydrate low-fat diets.