There are certain fundamental principles which should govern the dietitian, the physician, the nurse, and the mother, in choosing a diet for those under their care. In the first place, if one is choosing a diet for one individual, he should take into consideration, first of all, the age, next the health of the individual, and finally the conditions under which the individual is living, whether active or inactive, indoors or outdoors. Other factors that may be taken into consideration are the tastes of the individual and the cost of food materials. Considering the complexity of a combination of these factors, when the head of a household is required to arrange a dietary for a family in which there are old and young, robust and frail, and to keep this dietary within a certain stipulated sum of money, it is evident that the problem is not an easy one. The most important fundamental thing to determine is the amount of protein which is to be given. If the individuals who are to be provided are robust and active, the high protein diet may be selected with perfect confidence that it will be taken care of by the individual. Having decided on the amount of protein which the diet is to represent, one should next consider the form in which this protein is to be given. Upon this decision will depend largely the general character of the dietary, whether it is to be a mixed diet in which proteins are largely provided by lean beef, an ovo-lacto-vegetarian diet in which the protein is to be largely provided by eggs, milk, and legumes, or a vegetarian diet in which the proteins are to be found in legumes, cereals, and nuts only. The next thing to determine in regard to the diet is the amount and source of carbonaceous foods. Inasmuch as these foods include starches, fats, and sugars, it must be decided whether the diet shall be rich in fats or poor in fats. Perhaps the individual who is to be provided does not crave fats, which is a very common thing to observe. In that case the quota of carbonaceous foods must be made up largely from the carbohydrates. It may also be found that the individual cannot take large quantities of sugar because of a tendency to fermentation in the stomach, or in the case of the choice of fats, the individual may not be able to eat fat meat at all, but may relish cream and butter. After taking all of these things into consideration, the dietitian determines first the total energy which should be represented in the ration of one day. Next, the proportion between the three groups of organic foods - namely, proteins, fats, and carbohydrates. Let us suppose that the individual is a medium-sized man at moderate work out of doors, and that the man is in robust health and craves meat. We will choose a mixed diet and assign a ration of 125 grams of protein. Having chosen the high protein diet, we will take the low carbohydrate diet. If we had chosen the low protein we would have to take the high carbohydrates, in order to introduce into the diet the same caloric value.