Carbohydrates, whether of the starch group or the sugar group, are
composed chiefly of three elements: carbon, hydrogen, and oxygen; they
are therefore combustible, and are great energy producers. On the
other hand, they are worthless for cell growth and repair, and if we
limited our diet to carbohydrates, we should be like a man who had
fuel but no engine capable of using it.
62. The Fats. The best-known fats are butter, lard, olive oil, and
the fats of meats, cheese, and chocolate. When we test fats for fuel
values by means of a calorimeter (Fig. 26), we find that they yield
twice as much heat as the carbohydrates, but that they burn out more
quickly. Dwellers in cold climates must constantly eat large
quantities of fatty foods if they are to keep their bodies warm and
survive the extreme cold. Cod liver oil is an excellent food medicine,
and if taken in winter serves to warm the body and to protect it
against the rigors of cold weather. The average person avoids fatty
foods in summer, knowing from experience that rich foods make him warm
and uncomfortable. The harder we work and the colder the weather, the
more food of that kind do we require; it is said that a lumberman
doing heavy out-of-door work in cold climates needs three times as
much food as a city clerk. Most of our fats, like lard and butter, are
of animal origin; some of them, however, like olive oil, peanut
butter, and coconut oil, are of plant origin.
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