Fats are composed of carbon, hydrogen, and oxygen, but have much more carbon than the other kinds of foodstuffs. Notice in Fig. 46 that olive oil and lard are pure fats the other fat foods containing water, protein, and ash. Fat is available in various forms, with differing flavors and a wide range of prices. To many people it is unpalatable in some of its cheapest forms; yet its use is important, and some kind should be included in the diet. Fluid and emulsified fats are the most easily digested, hence olive oil, cream, and egg yolk are highly desirable. Bacon and butter belong nearly in the same class. A vigorous man at hard labor can digest fat of any kind without difficulty, and needs it because it gives so much fuel in proportion to its bulk.

Fat tends to retard gastric digestion, and delicate persons must be careful about taking with it other foods which are hard to digest, or taking it in the form of fried foods, pastries, rich cakes, and sauces. Persons with delicate appetite, who lose weight because they do not get enough fuel, may be benefited by taking a little more fat in the diet, especially if they do not digest starch and sugar readily, but a very large amount (over 6 or 7 ounces a day) will not be perfectly digested.