WHAT is a food? This is not quite so easy a question to answer as some people might suppose. Any substance which is capable of being digested and converted into the tissues of the body is a food. This is the scientific definition; but there are many substances which have been eaten, and which have actually helped to sustain life under emergencies, which we are not in the habit of looking upon as food in an ordinary way. For instance, in times of siege, leather has been actually eaten by starving people, but we don’t consider leather a food. Therefore in practical life it is only those substances which contain a considerable amount of digestible material that are to be regarded as foods.
Moreover, the question, What is a food? can only be answered by each individual for himself. What is a food to one man is not necessarily a food to another. Such an innocent thing as mutton, for instance, would be said by most people to be good food for everybody, and yet I know those to whom the least bit of mutton is dangerous poison. Many people can eat mackerel and enjoy it without feeling any after-effect; in others the smallest portion of it will set up choleraic symptoms. Some people are so sensitive that fish of any kind will cause violent nettlerash. I have known others who are sure to have a severe fit of asthma if they even smell roast hare. Finally, some people are poisoned if they eat rice, and can detect its presence in beer by their symptoms when merely a few grains of it have been put into the beer at the time of bottling.
In our definition of “food,” therefore, we must make room for exceptions; it is not all substances containing nutriment that are food for everybody.
Foods are divided into two kinds–those in which the nitrogenous or albuminous elements predominate, and those which contain the carbon elements in the greater proportion.
To the nitrogen class belong lean of meat, cheese, French beans, peas, lentils; whereas the carbon class is represented by fat of meat, butter, farinaceous foods, sugar, potatoes, and bread. The only perfect food is milk, containing both elements in good proportions. Eggs also contain both elements, but they are not such a perfect food as milk, as they do not contain the necessary salts in solution as milk does. Of course, there are other things in foods besides these two predominating elements, though this division makes a useful classification. And it must not be supposed that the members of one class have none of the elements characteristic of the other. It is only the proportion which serves to distinguish them; meat contains carbon as well as nitrogen, and bread contains nitrogen as well as carbon. Nor are the members of the same class alike; rice and bread are both in the carbon class, but rice contains less nitrogen than bread.
There is another food element the importance of which has been rightly emphasised by Dr. Lahmann, namely, food-salts. These are contained in milk in the right proportion as regards other food elements, and also in the right relative proportions among themselves. Soda, potash, and lime salts are the principal. These are contained in the various fruits and vegetables in sufficient excess to make up for the deficiency of them in meats, and pulse foods, such as peas, beans, and lentils. It is important that vegetables should be cooked by steaming, as the common practice of boiling them boils most of their salts out of them and common table-salt does not make up for the deficiency.
Cow’s milk contains 0.7 per cent. of food salts, which have the following percentage composition :-
Potash, K2O…. 24.67
Soda, Na2O…. 9.70
Lime, CaO…… 22.05
Magnesia, MgO…. 3.05
Oxide of Iron, Fe2O3.. 0.53
Phosphoric Acid, H3PO4.. 28.45
Sulphuric Acid, SO3.. 0.30
Silicic Acid, SiO2…. 0.04
Chlorine, Cl…. 14.28
Meat, white flour, potato, and peas contain very much less than the proper proportion of soda, lime, and chlorine than the standard of milk. Spinach, cabbage-lettuce, and carrot contain more than the standard. Apple and strawberry contain more than the standard of soda but less of lime. This shows the necessity of plenty of fresh fruits and green vegetables in the dietary of a meat-eating people. The use of common table-salt is no substitute for the lack of the right food-salts. Chloride of sodium is more of a stimulant than a food. It renders too rapid the passage of fluid from the tissues and causes an abnormal thirst. Salted meats are not such valuable foods as fresh meats; and for this reason : Three-fourths of the weight of fresh meat consists of water; but in contact with salt fresh meat loses some of its water, which passes into the brine and carries with it a considerable part of the effective organic and inorganic constituents of the meat (Group-Besanez). A similar process of “pickling” goes on in the bodies of those who eat excessively of salt. Another effect of over-indulgence in salt is the creation of acidity.