Carbohydrates are the main energy source of the human diet. The metabolic disposal of dietary carbohydrates is direct oxidation in various tissues, glycogen synthesis (in liver and muscles), and hepatic de novo lipogenesis. This latter pathway is quantitatively not important in man because under most conditions the rate of de novo lipogenesis does not exceed the concomitant rate of lipid oxidation in the whole body. Thus, dietary carbohydrates do not appear to increase an individual's fat content by de novo lipogenesis. The intake of dietary carbohydrates mainly has the effect of inhibiting fat oxidation while glucose oxidation is increased. Dietary carbohydrates are involved in the control of energy balance because the regulation of food intake depends, in part, on the carbohydrate need of the individual. Because there is an obligatory requirement for glucose in several organs such as the brain, a spontaneous increase in food intake is seen when the diet has a low-carbohydrate, high-fat content. Therefore, the present nutritional advice of increasing the proportion of carbohydrate energy while decreasing that of fat in the everyday diet has strong scientific support in terms of the regulation of the energy balance.