Since one or two classes of individuals, even though abnormal, show a lowered basal metabolism mainly as the result of a considerable degree of emaciation, it is a legitimate question as to whether or not a dietetic regime which leads to a moderate loss of flesh in normal subjects may not result in a lowered basal metabolism. Undernutrition is caused by a deficiency in food intake; this deficiency may be due either to a deficiency in protein or in calories in the diet.1

Protein Intake

The problem of a reduced food intake has received attention from physiologists for several generations, but interest has been centered for the most part upon the possibility of lowering the intake of protein. As the result of the heroic experiments of Professor Chittenden and his school at New Haven, the idea has gained credence (certainly with the American public and practically all physiologists) that a large protein intake is neither necessary nor desirable; on the other hand, that there should be an extensive reduction in protein is by no means accepted by all. One may sum up the situation by stating that the experiments of Professor Chittenden have unquestionably had a strong influence upon physiological thought in favor of a material reduction in the protein intake. It is safe to say that to most minds the reduction in protein is desirable mainly from an economic standpoint rather than from absolute physiological danger due to the ingestion of so-called "enormous" amounts; but it is undoubtedly true that a reduction in protein may certainly be made without danger. The most important point, however, at the present time is not the question of protein intake, but that of the total energy intake.

Energy Intake

It is a common household observation that people eat too much, the popular quantitative expression being that " people eat twice as much as they ought." Almost every household has its dietetic peculiarities, one individual eating very heartily, while another is said to eat "hardly enough to keep a canary alive." Yet careful studies of groups of individuals living under the same conditions show that ordinarily the total food consumption for like groups of individuals does not vary widely, and it would thus appear that the intake of food is adjusted in general to the demand of the body for fuel. This is best shown by the fact that, after maturity, the body-weight for the majority of individuals does not change widely for periods of years. Since the law of the conservation of energy obtains in the human body, the food intake thus corresponds on the average to the demands for energy. When food is absorbed, it can be disposed of in but two ways, either burned or stored as fat. If stored as fat, the weight would increase; if burned, the metabolism has been increased. Since the basal metabolism of an individual remains reasonably constant, any great increase in metabolism must be due to an increase in activity, i. e., muscular work. Consequently experimental evidence points to the fact that the ordinary dietetic habits of a community are usually adjusted to its needs for metabolic level and muscular activity.

1 Although without bearing on this research (see page 260), the detrimental effects of a deficiency in the so-called food accessory substances must not be overlooked in any basic consideration of undernutrition.

Recently the food stringency in Germany has thrown new light upon the possibilities of establishing lower nutritional levels by reducing the intake of food and lowering the body-weight.