Thanks to the careful and lengthened studies and the recorded observations of physicians and sanitarians, more especially of prison and army doctors, there is no subject in physiology on which we possess such accurate information as the amount and kind of food to be taken in proportion to the amount of work to be done. If the body be closely watched it will be found that it responds in its capacity for work to its food supply, as accurately and delicately as does the steam engine to its fuel supply. Without fuel, and the proper supply of fuel, force cannot be got from the engine, and without food and its proper supply in amount and quality, work cannot be got from the human creature. A person may indeed subsist on very low diet, or even exist in a quiescent state for some time without food at all, if supplied with water; but a life of health and vigour can only be maintained on the condition that the body is properly fed and nourished. To ascertain what is the proper amount of nourishment is my object.

Subsistence Diet

We learn from studying prison dietaries, the feeding of famine-stricken populations, and the diet of our own poor in London, what is the smallest amount of food on which the body can live, but not do hard work. This is three pounds of meat, with a pound of fat on it, or the same quantity of butter or lard, two quartern loaves, and about an ounce of salt per week. For meat, if unattainable, can be substituted two extra quartern loaves, or about a stone and a half of potatoes, or between 5 lbs. and 6 lbs. of oatmeal. Thus, we see that a person can actually exist on four quartern loaves and a pound of butter or lard a week without being gradually starved. This is, however, the diet of bare existence; on it a person can do no work bodily or mental, or he will certainly break down. Children, it must be remembered, in whom tissue change is rapid and growth is taking place, require more than a subsistence diet.

A Working Diet

Work may be divided into three degrees: I. Moderate, which may be represented by a daily walk of from five to seven miles. Such is the amount of work done by soldiers on home service, by clerks, or ordinary persons in easy circumstances. For this, judging from army dietaries, 5 lbs. of meat and 7 lbs. of bread weekly, with the addition of vegetables and milk, are sufficient. 2. Active work, such as is accomplished by soldiers on campaign, letter-carriers, and artisans, and which may be represented by a walk of twenty miles. This requires a fifth more nitrogenous food and added starchy and fatty foods. 3. Hard work means the work got through by navvies, miners, etc. As a rule these men eat increased quantities of meat if they can afford to do so. Science teaches, however, that in this they err; and that the force for hard work can be got at much less expense to the purse, and more easily by the body, from certain vegetables and from starchy and fatty foods than from large quantities of meat. An exclusively meat diet is wasteful as well as costly.