The proper amount of fat which is required in the diet during growth has not been and cannot be established since the exact rôle of fat has not yet been determined. Until recently it has been generally supposed that fat did not play any specific part in nutrition, but like carbohydrate, served as a source of energy and as a sparer of protein. In fact, many observers have believed that fat and carbohydrate are practically interchangeable in the diet. Because of this belief little attention has been given to the amount of fat which is desirable in the diet, except in the case of infants. Recent investigations, however, have shown that fat is of greater importance than was formerly believed and that it has specific functions quite apart from those which it shares with the carbohydrates. It has been shown that especially during growth fat is essential. There are now