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Page 196 NOTE ON METHODS OF ASSESSING THE ADEQUACY OF THE
ODS:
NATIONAL DIET
1. Three main criteria* may be used to assess the adequacy of the national diet its calorie value, its content of certain specific nutrients (notably of protein, mineral elements and vitamins), and its variety and acceptability.
The Calorie Value of the Diet
2. The outstanding importance of the calorie value of the diet has been established from theoretical considerations, by experiments on individuals, by feeding trials on selected groups of human subjects, and by observations of the effects of varying calorie levels on the body weights of large samples of the population.
3. Theoretical considerations, confirmed by individual experiments, have shown that an inadequate calorie level results either in a reduction in energy output (e.g., in muscular work and hence-on a national scale-in industrial productivity) or, if this is maintained, in a loss of bodyweight.
4. This observation has since been strikingly confirmed in field tests carried out in Germany during the war. These tests showed that, by increasing the food supply of a typical group of workmen by 500 calories per day, the rate at which they moved debris was raised from 1.5 tons to 2-2 tons per hour, though the workers still maintained an average gain in bodyweight equivalent to about half a stone a year. Similar studies made with other groups of workers, notably Ruhr miners, showed that, failing such special incentives, work output fell as a result of cuts in the rations which reduced the calorie supply below the level needed to maintain both output and bodyweight-i.e., the workers unconsciously tended to reduce their output rather than incur bodyweight losses. The sponsors of the German studies concluded that "rationing of food (below calorie requirements) also means rationing industrial production."
5. The practical problem is, however, not merely to determine what such calorie requirements are for the workers concerned, but to translate these into terms of a national average designed to cover the needs of a population of widely different ages and containing individuals whose occupations involve widely differing levels of activity.
6. Calculations from recognised tables of nutrient requirements, such as those contained in the 1950 Report of the Committee on Nutrition of the British Medical Association, indicate that-after making allowances for losses between the retail stage and the consumer's plate-the national requirement would work out at between 2,840 and 3,000 calories per head per day.
7. The validity of these limits was supported by experience in the pre-war and early war years. Before the war the calorie level of the national diet was about 3,000. By 1940-41 food shortages had reduced this figure to about 2,800. In the Report on Food Consumption Levels prepared by a Joint Committee of the Combined Food Board and published in 1944 the following comment is made (p. 37):-
"Some clue to the lower limit of supplies comes from United Kingdom experience in the period of greatest stringency since the war began, viz., in early 1941. At that time supplies fell to an average of less than 2,700 calories per head per day and although rationing was well established, there were indications of impaired health and working efficiency. General experi- ence tends to show that while the current United Kingdom supply level is adequate, the slightly lower level in 1941 was less than adequate, though some allowance must be made for the rapidity with which consumption levels fell in 1940-41. In other words the present supply level of about 2,800 calories per head per day is for the United Kingdom about marginal.'
8. At the time this Report was being prepared the Joint Committee did not possess any quantitative measure of the adequacy of the calorie level other than
* Excluding criteria based on health indices, such as bodyweight changes, clinical examinations and morbidity and mortality rates. But the requirement figures included in these notes are, of course, ultimately based on experimental and field observations of the relation of such indices to varying levels of food consumption.
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