NOTE.—For the benefit of lay readers, _metabolism_, a word
frequently made use of, may be defined as a term applied to the
collective chemical changes taking place in living matter. When
these metabolic changes are constructive, as in the building
up of tissue protoplasm from the absorbed food material, they
are termed _anabolic_; when they are destructive, as in the
breaking down of living matter or in the decomposition of
the materials stored up in the tissues and organs, they are
termed _katabolic_. Proteid metabolism, or more exactly proteid
katabolism, therefore, means the destructive decomposition
of proteid or albuminous matter in the living body and is
practically synonymous with nitrogenous metabolism, since the
entire nitrogen income is mainly supplied by the proteids or
albuminous matters of the food. The chief carbon income, on
the other hand, is supplied by fats and carbohydrates, such as
starches and sugars.
As the result of many years of observation and experiment certain
general conclusions have been arrived at regarding the requisite amounts
of food necessary for the maintenance of health and strength. Certain
dietary standards have been set up which have found more or less general
acceptance in most parts of the civilized world; standards which have
been reinforced and added to by man’s aptitude for self-indulgence. Carl
Voit, of Munich, whose long and successful life as a student of Nutrition
renders his conclusions of great value, considers that an adult man of
average body-weight (70-75 kilos) doing moderate muscular work requires
daily 118 grams of proteid or albuminous food, of which 105 grams should
be absorbable, 56 grams of fat, and 500 grams of carbohydrate, with
a total fuel value of over 3000 large calories, in order to maintain
the body in equilibrium. The Voit standard or daily diet is accepted
more or less generally as representing the needs of the body under
normal conditions of life, and the conclusions arrived at by other
investigators along these same lines have been more or less in accord
with Voit’s figures. In confirmation of this statement the following data
may be quoted: