Foods, their selection and preparation

The physical form in which the food is taken may affect the ease and completeness of digestion. Hard, compact cheese is more difficult to digest than the same cheese grated or with the particles separated by being mixed with some other foodstuff. Tough meat is more digestible when ground or when the connective tissue has been softened by cooking. The nutrients of certain vegetable foods are more accessible after the cellulose has been softened. Starches are rendered more easily digested by cooking. Most protein foods are easier to digest after cooking at temperatures below boiling than when cooked at higher temperatures. At high temperatures proteins harden and may form masses which digestive juices penetrate with difficulty. In selecting a method of preparation for any food, the foregoing factors must be balanced. One method may improve the flavor of the food, its appearance, and its physical form, but overcook the protein. In general, the tendency in food preparation is to favor methods which increase palatability, if not at too great sacrifice of other factors. Absorption of Food. After the foods have been digested, they must be absorbed. The calculated percentage of absorption of the different food nutrients is arrived at by a comparison of the composition of the food consumed with the food residue. Since the feces contain not only undigested and unabsorbed food but also residues from the diges¬ tive juices, intestinal debris, and bacteria, the results are approximate. General percentages for probable absorp¬ tion of the three basic components of foods have been established as follows: protein, 92 per cent; fat, 95 per cent; and carbohydrates, 98 per cent. These percentages will vary, depending upon the food source of the nutrient and the amount of undigestible ma¬ terial it contains. In the past, too much attention has been paid to the completeness of absorption of a food. Many persons suffer from constipation as a result of the use of too large a proportion of highly refined foods which are too com¬ pletely absorbed. Certain groups of foods are now recommended for the residue they leave, and the influence of this residue on elimi¬ nation. The degree of absorption of the nutrients in any food is largely controlled by two fac¬ tors: the completeness of the digestion of all the components of the food and the rapidity of its passage through the intestinal tract. Those foodstuffs are most completely ab¬ sorbed which contain the smallest amount of indigestible material. Animal foods, on this account, are very completely absorbed. On the other hand, water-retaining residues such as result from cellulose-containing vegetables and fruits are desirable to promote normal elimination. An important value in a mixed diet lies in the possibility of combining foods which leave the amount of residue best adapted to the individual need. Any condi¬ tion which hastens the passage of the food residue through the small intestine decreases absorption. THE ENERGY IN FOOD As food is digested and absorbed, portions needed to form the body’s own tissues and fluids are used; other portions are burned as an immediate source of energy; and any ex¬ cess is stored in the form of fat, sugar, or glycogen for use as needed. The food be- comes a part of the living organism from which later it may be thrown off as waste or inert material. o