Flesh contains no starch or sugar, but a small quantity of glycogen.  The fat in an animal is derived from the carbohydrates, the fats and the proteids of the vegetables consumed.  The soil that produced the herbage, grain and roots consumed by cattle, in most cases could have produced food capable of direct utilisation by man.  By passing the product of the soil through animals there is an enormous economic loss, as the greater part of that food is dissipated in maintaining the life and growth; little remains as flesh when the animal is delivered into the hands of the butcher.  Some imagine that flesh food is more easily converted into flesh and blood in our bodies and is consequently more valuable than similar constituents in vegetables, but such is not the case.  Fat, whether from flesh or from vegetables is digested in the same manner.  The proteids of flesh, like those of vegetables, are converted into peptone by the digestive juices—­taking the form of a perfectly diffusible liquid—­otherwise they could not be absorbed and utilised by the body.  Thus the products of digestion of both animal and vegetable proteids and fats are the same.  Formerly, proteid matter was looked upon as the most valuable part of the food, and a large proportion was thought necessary for hard work.  It was thought to be required, not only for the construction of the muscle substance, but to be utilised in proportion to muscular exertion.  These views are now known to be wrong.  A comparatively small quantity of proteid matter, such as is easily obtained from vegetable food, is ample for the general needs of the body.  Increased muscular exertion requires but a slight increase of this food constituent.  It is the carbohydrates, or carbohydrates and fats that should be eaten in larger quantity, as these are the main source of muscular energy.  The fact that animals, capable of the most prolonged and powerful exertion, thrive on vegetables of comparatively low proteid value, and that millions of the strongest races have subsisted on what most Englishmen would consider a meagre vegetarian diet, should have been sufficient evidence against the earlier view.

A comparison of flesh and vegetable food, shows in flesh an excessive quantity of proteid matter, a very small quantity of glycogen (the animal equivalent of starch and sugar) and a variable quantity of fat.  Vegetable food differs much, but as a rule it contains a much smaller quantity of proteid matter, a large proportion of starch and sugar and a small quantity of fat.  Some vegetable foods, particularly nuts, contain much fat.

Investigation of the digestive processes has shown that the carbohydrates and fats entail little strain on the system; their ultimate products are water and carbon dioxide, which are easily disposed of.  The changes which the proteids undergo in the body are very complicated.  There is ample provision in the body for their digestion, metabolism, and final rejection, when taken in moderate quantity, as is the case in a dietary of vegetables.  The proteids in the human body, after fulfilling their purpose, are in part expelled in the same way as the carbohydrates; but the principal part, including all the nitrogen, is expelled by the kidneys in the form of urea (a very soluble substance), and a small quantity of uric acid in the form of quadurates.