Of what plants and animals make human foods and how they do this is considered later. The result of their food-manufacture is that human food is both vegetable and animal. Both serve in some respects the same purpose in the body, while in others their use is different. Either vegetable or animal food would sustain life, but both together do so much better than either could. Vegetable food would do better alone than animal. Not a few persons do live upon it entirely. There are, however, reasons that make food-scientists doubt the advisability of an exclusively vegetable diet. But Science (now advises that somewhat more than one half (at least .56) of the food of humankind be vegetable.

Plant food supplies most of the energy and endurance of the body in starch, sugar, and vegetable-oil foods; also much of the body-heat, the food-bulk required for digestive activity, the salts needed for body-regulation, and the water used in living processes and food-utilization) Some vegetable food can also build up body-tissue as it needs repair or material for growth.

Vegetables, fruits, and seeds are of plant production. What these are like and where they come from, how they come, are prepared and used, are the food-facts that show what the food-supply brings to humankind as its vegetable food.

Looking back of the food as served is seen the life of the plant itself, also the work of those that bring it to humankind as a human food that will nourish when eaten. Seeking such facts and seeing them as factors controlling the sustenance of human-ity is the purpose of studying Food - What it is and does.

What vegetable food is used in human living is learned from markets that show what foods are available and from science that finds what foods can be produced and supplied, also what kinds of food are needed.