DIET AND NUTRITION
by ELMER V. MCCOLLUM
WHAT we know about the nutritive needs of the human body and about quality in foods is the result of experimental studies on animals, correlated with such observations as can be made on human subjects. Between 1840 and about 1905, an adequate diet was generally described as consisting of appropriate proportions of proteins, carbohydrates, fats, mineral salts, and water. Oxygen of the air should have been regarded as a nutrient principle, since without it food could not be utilized; but it was not ordinarily included in the list, except as it formed part of the molecules of the foods ingested. Since this date, our knowledge of dietary requirements has advanced materially, and is still advancing, though perhaps nearing completion. The most profitable method of study has been found in efforts to simplify the diet, in order to learn what chemical substances are indispensable, and which of the compounds known to occur in the tissues are capable of being synthesized by the body.
Proteins consist of giant molecules which are resolved during digestion into about twenty relatively simple organic compounds known as amino-acids. We know that two of these can be synthesized by the body, and, pending further investigations, we may assume that the remaining eighteen must be supplied by the food. We must have the sugar glucose, which may be taken as such or derived from cane or milk sugar or from the various starches. These are