Very low‐calorie diets (400 kcal:1.7 MJ) with different proportions of carbohydrate, protein and fat were given to obese in‐patients for 1 week using a Latin Square study design. This type of diet with a relatively high carbohydrate content produced a smaller weight loss when compared with diets with relatively high protein or fat content. In a second study, two very low‐calorie diets with a high or low carbohydrate content were compared in a randomized cross‐over design in obese patients for 1 week. Those patients receiving the diet with high carbohydrate content had a significantly lower weight loss. In a third study, these diets were continued for 2 weeks. A significant difference in weight loss was observed in the first week but not the second. In a fourth study the same effect of carbohydrate content was also observed using low‐calorie diets (800 kcal:3.4 MJ) for one week in obese patients. The explanation of this effect appears to be a decrease in the diuresis which usually accompanies the introduction of a very low‐c