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Foods may be considered under different classifications. First, as to general appearance and use three classes may be made,—foods, beverages and condiments. As types of the first division of these foods may be mentioned cereals and their preparations, meat and its preparations (except meat extracts), fish, fowl, and game. Beverages are those liquid food products which are more valued for their taste and flavor than actual nutritive value. As types of beverages may be mentioned wines, beers, distilled spirits and liquors of all characters, tea, coffee, cocoa, chocolate, etc. Under wines, in this sense, may be included the fermented beverages made of fruit juices, such as cider, perry, etc. Types of condiments are salt, pepper, spices, vinegar, etc. Milk, although a liquid substance, is hardly to be considered a beverage, and on account of its high nutritive properties may be classed, together with its preparations, under the first head.

Foods may also be classified as nitrogenous, starchy, oily, and condimental. Nitrogenous foods are those in which the proportion of their material containing nitrogen is large. Lean meat may be regarded as a type of nitrogenous food, since it consists almost exclusively of tissues known as protein and contains nitrogen and sulfur as essential ingredients. The white of an egg is also a typical nitrogenous food and, to a less extent, the yolk. Among vegetables, peas and beans are typical foods containing large percentages of nitrogenous matter. The gluten of wheat is also a typical nitrogenous food and the zein of Indian corn, corresponding to gluten, is a nitrogenous material.

Practically all the vegetables used as foods contain more or less protein in their constituents. Among the cereals oats has the largest quantity and rice the smallest of this valuable food material. Of oily foods the fat of animals, including butter, is a typical representative. All meats, fish, fowl, and game contain more or less fat. Of vegetables and fruits there are many which contain large quantities of fat, such as nuts, oily seeds, etc. All vegetables contain more or less fat, although the succulent vegetables usually contain but little thereof. Of starchy foods there are no types in animal food, the quantity of carbohydrate material therein being extremely limited. The lobster and horse-flesh contain perhaps a little more than 1 percent of carbohydrate food, but most meats contain much less than that. Sugar and starch are typical carbohydrate foods.

The cereal grains are composed largely of starchy foods, and so are certain tubers, such as the potato, cassava, etc. Of the common cereals rice contains more starch than any other and oats the least. Sugars are intimately related to starch and are included under the term starchy food or carbohydrate food. The carbohydrate matter in the flesh mentioned above, namely glycogen, is of the nature of a sugar. Among the typical sugar foods are beets, melons, and fruits, some of which contain large percentages of sugar. All fruits contain greater or less quantities of sugar, and that is true, also, of all vegetables.

Of the plants which produce the sugar of commerce there may be mentioned the sugar-cane, the sugar-beet, the maple, and palm trees. The principal sources of the sugar of commerce are the sugar-cane and the sugar-beet.

Of the condimental foods may be mentioned spices, including pepper, mustard, cinnamon, allspice, and other foods of this class. Common salt occupies a unique position in food products. It is the only mineral substance which has any value as a condiment in human food. But it also has a more important function than its condimental character, namely, it furnishes the supply of hydrochloric acid without which digestion in the stomach could not take place. For this reason common salt must be regarded as an essential food product as well as a condiment.