The Interrelationship of Foodstuffs in Metabolism

Like every panel of physiology or medicine, metabolism has been studied and taught by the categorical method. But, for a full understanding of the subject, synthesis and integration are essential. Energy production and caloric needs are only significant when the purposes to which the energy is directed are taken into account. It may be useful to regard the body as a complex industrial plant or machine. Power to run this plant could be derived from a variety of fuels, such as wood, coal, or oil. The counterparts of these in the physiological factory are carbohydrate, fat, and protein. The nmere combustion of these for the production of power may be called the energy metabolism. The efficiency of the power plant will vary-first, with the nature of the fuel; secondly, with the device used for its combustion. This will have to be different and appropriate for each fuel. The mere prodtiction of heat, though essential for its operation, is not, however, the object of this plant. The heat must be directed to useful ends. This requires highly specialized machinery for which particular materials must be provided. Some of these can be manufactured on the premises; others must be supplied ready-made. This machinery must be integrated and must be equipped with regulating devices to permit variations in the relative speeds Of its multifarious processes. It has been suggested that these phases of metabolism be termed operative metabolism, in contradistinction to energy metabolism. Until recently operative metabolism has been an almost unpenetrated mystery. This mystery is now being dispelled with such rapidity that it is hard to keep pace with the advances. It is impossible in a single article to detail these discoveries; an attempt will be made through certain examples to convey some impression of the modern dynamic concept of metabolism which deals with chemical compounds not as mere substances, but as instruments. Since provision of power is the ultimate limiting factor, it may as well receive attention first. Any one of the three foodstuffs-fat, carbohydrate, or protein-may serve as fuel for this plant, but not indifferently. No one of them is altogether indispensible because each has an operative as well as an energy-producing function. A small amount of carbohydrate is essential for purposes that will be outlined later. If adequate and continuous amounts are not supplied in the food, the body is compelled to manufacture it. The only