These four kinds of food substance make up our daily food, and a certain amount of each substance is required to replace the daily expenditure, a proportion which varies, however, under different circumstances. _See_ Food in Health.
As the relative amount of proteid, carbonaceous matter, water, and salts, may vary considerably in different articles, we rightly have combinations of food at our meals. A pudding of corn-flour and water contains no building material, hence we add milk and eggs, which do. A meal of meat and cheese requires bread and potatoes, etc., etc.
Appetite is a good test of the amount and also of the particular kind of food required, provided the appetite is in a healthy condition. If a healthy man refrain from carbonaceous foods for a day or so, he feels a great longing for them, a sign that the body really needs them. It is of immense importance, then, that the appetite should not be accustomed to over-indulgence, for then it is no guide in our selection of foods (_see_ Appetite). If disease indicates such over-indulgence, food should be restricted till the appetite is accustomed to a smaller diet. Bilious people, for example, may have accustomed their appetite to desire more carbonaceous and fatty foods than necessary. On the contrary, badly-fed people often require a coaxing of the appetite to eat strengthening foods, such as oatmeal, cheese, and brown bread.
In order to regulate our diet, it is of importance to have some idea of the composition of common articles of food. We get our food, as everybody knows, from the vegetable and animal kingdoms. The majority of the Anglo-Saxon race live on a diet of animal and vegetable combined, but many exclude flesh from their diet. In Southern Asia, for example, the vast bulk of the people rarely, or never, touch meat. The vegetable kingdom supplies us largely with the carbonaceous or muscle-forming food, whereas the animal kingdom is rich in proteid, or tissue-forming food. Much proteid, however, can be obtained from the vegetable kingdom--peas, beans, lentils, dried fruits, and nuts being particularly rich in it. We should endeavour to cultivate an appetite for these vegetables containing proteid, as it is a great mistake to rely entirely for this element on meat, as so many of our race do. The animal products--such as cheese, milk, and eggs--will also form an efficient substitute for much flesh-food. This simple diet suits both the brain-worker and the athlete, though each will have to make a selection of those foods most required by him. Certainly much animal food is liable to produce kidney disease, gout, and kindred troubles. If we have a tendency to corpulence (and many have this in advancing years), to resort to an exclusive meat diet will produce these troubles. Far better abstain from vegetables, such as potatoes, and from sweet dishes, pastry, etc., and eat largely of the green-leaf vegetables and fruits with the articles of a simple diet which build but do not fatten the body. (_See_ Diet and Corpulence; Diet for Middle Age, and the Aged.)