For years dietary guidelines for the treatment of overweight and obesity have advised a low-fat, high carbohydrate diet. Recent meta-analyses have shown that weight loss achieved with ad libitum low-fat diets is typically in the range of 3-4 kg. Although clinically significant, this weight loss is modest, usually regained on cessation of the intervention and the low-fat messages have not impacted on the ever increasing rates of overweight and obesity. Alternative approaches include low-glycemic index and high protein diets. Both effectively reduce the glycemic load of the diet and early studies suggest they may be effective in increasing satiety, reducing ad libitum energy intake and may improve fat oxidation by reducing insulin demand. Both approaches can be used within the context of a reduced-fat diet, with evidence emerging to suggest this may improve weight and body composition outcomes.