Diet is one of the cornerstones of a weight loss programme. Although there is little evidence that diet composition plays a clinically important role in the absorption or expenditure of energy, it does appear to play a role in food intake. Diets with a deficit of 500-1000 kcal per day will produce weight losses of between 300 and 1000 g per week, depending on the patient's weight. Formulae for estimating energy intake are provided. Starvation diets with an energy intake below 200 kcal per day are no longer used, but very low-energy diets with an energy intake of between 200 and 800 kcal per day have been used, although there is little to support the use of energy levels below 800 kcal per day. Ad libitum low-fat diets have been reported to produce weight losses that average 1.6 g per day for each 1% reduction in the level of fat. In a meta-analysis, overweight subjects lost 5-7 kg before reaching a new plateau. In normal weight subjects, the loss was only 0.5 kg. A low-fat diet may be of value in helping patients to maintain their weight loss. Higher-protein diets were more effective than low-protein diets in one clinical trial. The type of carbohydrate in the low-fat diet does not appear to influence weight loss. Alcohol, on the other hand, is poorly satiating and may replace fat in oxidative processes, thus enhancing the risk of obesity.