The General Problem Of A Dietary Standard

It is sometimes asked whether a normal appetite does not indicate, as well as can any dietary standard, the amount of food which is desirable for an individual in any given circumstances.

In considering such a question we shall hardly expect the phrase "amount of food" to indicate equally the energy value, the protein content, the content of each of the necessary chemical elements, and each of the unidentified dietary essentials A and B (or fat soluble and water soluble "vitamines"). Since different articles of food vary greatly in the relative amounts of the various nutrients which they contain, some one aspect of food value must be chosen as a basis in order to give definite meaning to the phrase "amount of food." Inasmuch as the most prominent of the nutritive requirements is the need for energy, and the yielding of energy is the one function in which practically all articles of food take part, it is logical to expect that "amount of food" will more nearly express number of calories than any other one factor of food value or nutritive requirement. Observation confirms this impression and shows that men or other animals when eating varied food under the unrestricted guidance of hunger and appetite tend to take such quantities as are proportioned to the energy requirement whether or not this amount meets also the requirements as to each of the sixteen chemical elements known to be necessary in nutrition.

If then hunger and appetite be regarded as guides, primarily, to the eating of the right amount of food to meet the energy requirement, we may determine their adequacy in any given case by the fatness of the person concerned, since excess of fuel food of whatever kind can contribute to the storage of body fat.

If from year to year the body keeps in good condition for its work and maintains a fairly constant weight which bears such a proportion to the height as to show that a proper amount of fat is being carried, it is reasonably certain that the amount (fuel value) of food eaten in the course of the year is substantially that which is suited to the degree of activity maintained. If, however, by following the appetite, one becomes unduly stout or unduly thin, or does not get sufficient fuel for the energy required for the day's work, or is annoyed by digestive disturbances indicative of improper feeding, it is certain that the appetite is in this case not a perfect standard. Still more often will the individual appetite prove an inadequate guide to such a quantitative combination of the different types of food as shall lead to a well-balanced intake of each of the many essential food constituents. Here the customs and traditions which govern the food economics of the household and which undoubtedly to some extent reflect the accumulated experience of the race serve an extremely important purpose in checking the caprices of the palate and guiding the individual into food habits which are more likely to conform to actual needs than are the dictates of the individual appetite. But the fullest appreciation of the value of household and social traditions in the formation of good dietary habits does not justify the conclusion that such traditions will always lead to the best results, either physiologically or economically. Even if these traditions represented the experience of past generations to the fullest imaginable extent, they could not be expected to guide us in the use of foods which were not available to our predecessors but have now within a generation become a common part of the dietary. Nor is it reasonable to suppose that dietary habits adapted to people engaged chiefly in outdoor occupations under frontier conditions will be equally suited to the sedentary city worker of to-day. Under modern conditions scientific dietary standards, based on a knowledge of food chemistry and nutritive requirements such as the preceding chapters have attempted to give, constitute the most rational guide to the formation of hygienic and economic habits in the use of food.

The earliest attempts to set dietary standards in terms of nutrients were those of the German physiologists, among whom the most influential was Voit. He suggested as a proper daily allowance of foodstuffs for a man at moderate muscular work:

Protein, 118 grams.

Fat, 56 grams.

Carbohydrates, 500 grams.

This dietary would have a fuel value of approximately 3000 Calories. The allowance of 118 grams of protein, which has since provoked considerable discussion, is said to have been based upon the average protein metabolism of many laboring men who were living apparently upon unrestricted diet, so that it was practically the result of dietary study. In the division of the remaining calories between fat and carbohydrate, Voit made the allowance of fat low and of carbohydrates high in order to cheapen the dietary.

In England, Playfair recommended as a standard for a man at moderate work:

Protein, 119 grams.

Fat, 51 grams.

Carbohydrates, 531 grams.

This would yield 3060 Calories and is evidently based quite directly upon Voit's recommendations.

In France, Gautier has proposed as a standard for men with little muscular work:

Protein, 107 grams.

Fat, 65 grams.

Carbohydrates, 407 grams.

This allowance of nutrients - which is based in part upon carbon and nitrogen balance experiments, in part upon studies of French families selected as typical, and in part upon the statistics of food consumed in Paris for a period of ten years -would supply 2630 Calories.