What one is used to eating often seems satisfying, even when it is not a satisfactory diet and is not doing for the body what only food in the combination needed can do. Food habits are formed as one eats and lives; they largely control the choice of food. This strength of habits should be used to aid the body, by making the diet needed by the person the usual familiar diet. The kind of food-combination that science has learned will give physical endurance and energy, will build and repair the body and assist it in using its food, is the necessity of every one and can be known by all. For children to form such a habit as that of tea- and coffee-drinking is to rob them of the opportunity of having well-nourished bodies.

Physical construction of the body, power of self-repair, living-energy in life-activity, all depend upon the food-regulation of the person; hence the importance of food habits, food tastes, and food practices. If the food eaten is not able to do these things, they are not done or only partly done. The body that is poorly nourished may live and do some work, but it is without resistance to disease, if not itself diseased. It is less strong as it is less well, also less effective in whatever it does.

If the food eaten is not used by the body, because the food chosen does not meet the need there is for food, the food is not only wasted but overburdens the body with food-waste; this hinders its action and if unremoved poisons it. Though building, energy, digestion foods can, as stated above, be found in either the animal foods or in vegetable, were they exclusively taken from either, the body would be overworked. Less work is required to use food from both together, because each food then digests more easily and fully, and the digestive tract in being thus used as a whole works better itself than when only part of it is used.