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food fats.

~Characteristics of Fats.~--The fats are all insoluble in water, and
only partially so in cold alcohol, but they dissolve readily in ether.
As a rule, the fat occurring in the animal body is more or less
characteristic of the species. For example, animals that live on land
have a harder fat than those living in the water; warm blooded
animals, harder fats than cold blooded ones (fish); and carnivorous
animals, harder fats than herbivorous species.

Fats are lighter than water, hence will float in it. An emulsion is a
suspension of fat in a fluid, and the fat in this case must be very
finely divided and mixed with some other material which will prevent a
coalescence of the fat globules. In milk, which is one of the best
natural emulsions, the additional substance is protein.

~Effect of Heat upon Fat.~--When fats are brought to a high
temperature, the glycerine which they contain decomposes with the
production of a substance known as acrolein, which has an irritating
effect upon the mucous membranes. It is possible that the over-heated
fatty acids add their quota to the production of irritating fumes. As
a rule, it is inadvisable to use frying as a method of preparing food
for the sick or for children. Doubtless, if every cook understood the
exact degree of heat to apply in frying, and knew just how moist to
have the food mixture which she intended to cook in this manner,
better results would be obtained; but since the average cook knows
little about the scientific application of heat to fat or the changes
brought about thereby, it is safer to make use of other methods of
food preparation under the circumstances.

~Functions of Fat.~--This foodstuff undoubtedly serves as the most
compact form of fuel available to the body for the production of
energy. Weight for weight, fat furnishes twice as much heat as the
carbohydrates, and in bulk the difference is even more striking; for
example (about) two tablespoonfuls of sugar are required to produce
100 calories, whereas one scant tablespoonful of olive oil will
produce a like number of heat units. As a source of supply for reserve
energy in the body, fat is most valuable. This reserve fuel is stored
in the form of adipose tissues underlying the skin and surrounding the
vital organs, lending contour to the form and protecting the organs
from jars and shocks. Distributed throughout the body, fat may be
found as (a) cholesterol (in the cells of the muscles, or