Various systems of diet have been devised to meet the requirements of disease, the fancies of the faddist, and the desire of the layman to teach the members of the medical profession things of which they are thoroughly well informed. Some of these systems are based on the elimination of articles of food from the diet list, on aesthetic or humanitarian grounds. Others depend on theories about that bugbear of the lay imagination, "the uric acid diathesis." In many instances the particular modification is due to purely medical reasons, such as the desire for simplicity, the wish to give the digestive functions a complete rest from dealing with some one or other of the various food constituents, or the necessity for limiting the amount of nutriment in the diet without reducing the actual quantity thereof. Often it is merely a question of partial starvation for the time being. Many of the diets, which carry out this object, are those used in the treatment of obesity, and are referred to in that section. The diets dealt with in the present chapter are of use in various conditions of health and disease, in different climates, and for different individuals or the same individual under different conditions of life.