An Evaluation of the Balance of Nutrients in Milk

acids established variabil i ty in composition of proteins from different sources and introduced the concept of quality of protein. As the ash of milk was found to contain essential nutrients, fur ther experiments designed to study inorganic elements in nutrit ion revealed that milk contained essential food constituents not found in the known carbohydrates, proteins, fats, and salts (51). Prior to 1906, it had been suggested that scurvy and beriberi in humans were caused by specific dietary deficiencies, but this view was not universally accepted. The production of experimental scurvy in the guinea pig (42) and a disease resembling beriberi in pigeons (21) provided the important laboratory approach to the solution of the nutri t ional problems of humans. Experiments whose objective was to define the nutri t ionally important components of milk by using laboratory animals coupled with investigations of the human deficiency diseases firmly established the need for trace quantities of organic chemicals. Funk introduced the concept of "vitamine" in 1911 (25) to describe the missing organic factors necessary to cure beriberi and scurvy and to complete the diets of laboratory animals fed purified carbohydrate, protein, fat, and salts. During the past 44 years numerous new essential nutrients have been discovered, including certain essential amino acids and fa t ty acids, other vitamins, and trace minerals. Throughout the period when our modern concepts of nutri t ion were developing, milk has been looked upon with favor by nutrit ion workers because most of the food elements needed by man are found in good balance in milk. Preceding and parallel ing these advancements in our knowledge of nutri t ion have come important developments in chemistry and chemical technology. The organic chemist has been able to synthesize most of the essential organic food constituents, in some cases on a commercial scale. Synthetic products have been employed for improvement of the balance of nutrients in our food supply (59). There is reason to expect improvements in chemical technology to the point that most, if not all, of the critical essentials may be supplied in synthetic form to supplement any deficiencies that may exist in the natural food supply. Advances in food technology have also brought about the development of p lant products which compete with dai ry products. This competition has forced the dairy industry to reexamine all of its products and to think seriously in terms of supplying its nutri t ionally sound foods at competitive prices. Fortunately, the cow is highly efficient in her conversion of roughages unsuitable for human consumption into products which are useful foods for man (9). This efficiency coupled with the balance of nutrients in the product is the best argument for her future in meeting the demands for a balanced diet for expanding populations. Many of the people of the world are unable to obtain sufficient food for good health and resistance to disease. The first consideration for them is to get enough calories. In areas of the world where the food supply is adequate there is the problem of selecting the proper foods to provide a balanced intake of the required nutrients. Tables of recommended dietary allowances prepared by the Food and Nutri t ion Board of the National Research Council (60) and the minimum daily requirements of nutrients formulated by the U. S. Food and Drug Administrat ion are most useful guides to help with this problem. The recommended allowances are based upon clinical observations and upon an evaluation of the facts obtained by nutri t ion experiments with laboratory animals. The usual practice is to take the values obtained experimentally and increase them to obtain a recommended value. The purpose of this increase is to provide a margin of safety to insure adequate nutrient intake to meet various situations. These allowances serve as a useful guide for most of the population, but there is some evidence that sick, wounded, or convalescent