But that meals shall fulfil their office of renewing life and gladness, it is necessary that the woman who selects and arranges them shall have some knowledge and shall expend some care. It need not be elaborate knowledge, nor burdensome care, just a usual quantity of each.
It has been discovered that human bodies are composed of chemical elements just as are cabbages and doctors' prescriptions. Some of the elements of which we are composed are oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur, iron, potassium, calcium, and there are others yet. It would seem a simple matter to find out just how much of each of these things we contained and then to keep up the supply by eating or inhaling them in the required quantities, but you can be sure there is nothing as dull and matter-of-fact as that in this interesting creation. We are not doctors' prescriptions, we are even a bit more remarkable than cabbages, and it is not just correctly measured proportions of oxygen, nitrogen and potassium that we need, but energy, and heat, and flesh, and blood. Therefore, it is that when we consult some wise table of statistics in which the nourishing value of food is given, we do not find it given in terms of oxygen and hydrogen and the rest, but in terms which indicate heat, energy and building material.
Tables of the composition of foods are usually made in the following terms: Refuse, Water, Protein, Fat, Carbohydrates, Ash. Added to these there will often be a division headed "Calories." The calorie nevertheless is not a food substance, it is the unit by which energy-giving heat is measured. Just as a ribbon is measured in yards and molasses in cupfuls, so heat is measured in calories.
"Refuse" means that part of food which cannot be eaten or which could not be used by the body if it were eaten, as bones, fibres, seeds, parings, pods and shells.
"Protein" is an inclusive word for the chief substances in food which the body can use in rebuilding itself as use wears it out.
"Carbohydrates" are the fuel of the body. They are converted at once into heat and energy, or if there is a surplus they are often stored in the body in the form of fat to be used when nourishment is less abundant.