Although the complex details of intermediary metabolism remained to be discovered as the twentieth century began, the basic framework of the modern science of nutrition had been laid down. Free sugars and their polymers furnished glucose for bodily functions, including muscular work: Excess carbohydrate could be stored as glycogen and fats, thus providing a fuel reserve that could furnish energy during periods of fasting. The views of Liebig concerning heat and work were recognized as mistaken by Hutchison in his text of 1903:
We now know that bodily heat is not a thing apart and requiring to be provided for by itself, but that it is an inevitable accompaniment of cell life. Life and heat are inseparable, and in fulfilling its other function in the body a cell cannot help producing heat also (Hutchison 1903: 3).
Hutchison went on to indicate that as far as the cells of the body were concerned, it was a matter of indifference whether carbohydrate, protein, or fat were the original sources of the food energy. In strict energy terms this remains true, although the specific role of the energy sources, especially fat, in relation to chronic disease risk is now central to dietary guidance.
Lusk, author of several monographs and texts on nutrition (Lusk 1914, 1928, and 1933), and yet another who trained with Voit in Germany, dedicated the first edition of his monograph The Elements of the Science of Nutrition to his mentor in 1906. That an essentially modern view of nutrition had developed by this time can be seen from Lusk’s writing (1914:4):
The workshops of life require fuel to maintain them and a necessary function of nutrition is to furnish fuel to the organism so that the motions of life continue. Furthermore the workshops of life are in a constant state of partial breaking down and materials must be furnished to repair worn out parts. In the fuel factor and the repair factor lie the essence of the science of nutrition.
Lusk (1914) also held modern views on the social aspects of nutrition, as is indicated in his lecture to the New York Academy of Medicine, which advocated
Figure IV. C.3.2. An overview of the combustion of fuels for energy. Acetyl coenzyme A is formed from carbohydrates, fats, and amino acids. Whatever the source, a large fraction of it is oxidized to CO2 and H2O, although any excess may be used to form lipids as an energy reserve.
Nutritious school meals, family nutrition education, and national nutritional labeling of foods.
Another major activity in the early years of the twentieth century became the determination of the basal metabolic rate (BMR) in many subjects together with the development of prediction procedures for estimating BMR from body weight or from body surface area (Harris and Benedict 1919).The BMR is the rate of heat production, measured directly or indirectly, when the subject is at rest and has not eaten for several hours. The normal range for large populations was thought to be relatively narrow. Variations in the BMR of supposedly normal individuals were often attributed to carelessness in experimental procedure, rather than to the existence of real differences. The field of calorimetry became devoted mainly to examining abnormalities in BMR associated with various diseases, in particular, thyroid disease, diabetes, and the more common fevers.
Equipment for determining BMR was standard in hospital laboratories until about 1950, at which time new chemical methods for measuring materials in the urine and blood related to thyroid metabolism caused hospitals to abandon the measurement and, consequently, to terminate the last remaining quantitative approach to energy metabolism in patients. In the hospital environment, research on energy expenditure in surgical patients returned under the leadership of Kinney (1988), who utilized a head canopy system that was acceptable to acutely ill patients and still permitted medical care as required.
There has been an enormous resurgence of interest in energy balance studies in recent years as a result of the growing concern over the hazards of obesity and the realization that we still have much to learn about energy metabolism and the control of energy balance.
World History
