FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS	ESN: FAO/WHO/UNU EPR/81/40 September 1981
	WORLD HEALTH ORGANIZATION
	THE UNITED NATIONS UNIVERSITY

Agenda Item 4.1.1.

Joint FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements

Rome, 5 to 17 October 1981

VARIABILITY OF THE PROTEIN-CALORIE RATIO IN DIETS

by

J. Périssé and P. François
Food Policy and Nutrition Division
FAO

Introduction

The 1971 FAO/WHO meeting considered both energy and protein requirements. As the subject was not exhausted, it seemed interesting, with a view to the next consultation, to study the share of protein in energy intake of the diet and to observe its variability. This was done on the basis of family consumption data by weight over 5 to 7 days, no longer on the basis of food balance sheets (4).

It has been found since before the war that in many diets the calories supplied by protein expressed in percentage of total calories (protein-calorie ratio) varies within quite narrow limits. Sherman (1937) says that “well-planned dietaries for children usually contain between 10 and 15 percent of the total energy in the form of protein” (5). Widdowson (1947) states that “the results of dietary studies in various parts of the world all go to show that the majority of mankind take 10–15 percent of their calories in the form of protein..… this is one of the most constant features of the diets” (3).

Trémolières (1955) observes that the consumption of rural people in France is remarkably constant despite highly diverse food habits. He concludes, “It is perhaps possible to speak of a sort of physiological regulation of calorie intake and of nitrogen intake” (1). On the basis of 22 random surveys in the world, he finds, as did the foregoing authors, that “the protein-calorie ratio, in general, is remarkably constant and ranges from 11 to 14 percent”. He adds, “The 11 percent ratios seem to be the lower limit of what is well accepted. Protein generally is associated with very good acceptability of foods. When lower ratios are found, they are of short duration or accompanied by high consumption of spices, salt, alcohol or fermented products which play a compensatory role” (2).

The Environmental Factor

It should be pointed out that foods have greatly different protein-calorie ratios. Approximate values for the principal foods are as follows:

In theory, there are infinite combinations to distribute such foods so that the resulting food mixture has a protein-calorie ratio close to 12 percent. Free food choice, if it exists, is possible only in a money economy and in wealthy countries whereas it is limited by food habits and tradition and is channelled, not to say constrained, by the food associations needed to prepare dishes.

In a rural population with low money income, food purchases account for a small part of food intake and consumption of what they produce represents the major share. As a result, food patterns and ecological environment are closely related. Since on the other hand staple foods supply 60 to 85 percent of the calorie intake, the protein-calorie ratio of the whole diet depends strongly on the protein-calorie ratio of the staple foods. Animal products which could improve this ratio, sugar and fats which degrade it are in small quantities in the diet. The results of surveys made in Africa since 1950 illustrate this (6).

In areas with two rainy seasons (Table 1) (pre-forest Guinean zone of West Africa, Central Africa) and in southern Madagascar, the diet features very high consumption of roots, tubers and plantains and a limited intake of cereals (maize or rice). The protein-calorie ratio is less than 11 percent in 36 surveys out of 41 and often ranges from 7 to 10 percent.

Tables 2, 3 and 4 give the results of surveys among populations with a cereal diet. In Madagascar (Table 2) where food habits are of Indo-Malaysian origin, rice is the staple food virtually everywhere (7). The protein-calorie ratio of the diet is less than 10 percent, varying between 8.5 and 10.2 percent, depending on the area. In Tunisia (Table 3) where the diet is based on wheat, the protein-calorie ratio is higher - close to 11 percent - (10), (11).

In the arid regions of Africa south of the Sahara (Table 4) (Sudan and Sahel zone), millet and sorghum are the staple foods. The protein-calorie ratio in most cases ranges from 11 to 15 percent (6).

Lastly, some diets in East Africa (Table 5) in high-lying areas bordering on the Rift Valley show such a high consumption of pulses that, despite the presence of roots, tubers and plantains in the diet, the protein-calorie ratio amounts to 17 percent or more.

In the Arctic regions, the Eskimo populations depend for their food supply on fishing (salmon), hunting (seals, bears) and gathering (berries, shellfish, algae) (Table 6). In these diets consisting largely of meat and fish, the protein-calorie ratio is very high (30 to 45 percent) (8), (9).

Table 4 - AVERAGE PROTEIN CALORIE RATIOS IN MILLET AND SORGHUM DIETS (Africa, arid zone)

1 bread, barley, peas, sugar
2 grains products, sugar, fats, dairy products

These examples show indisputably that, contrary to what one might think, the protein-calorie ratio varies over a wide range (from 5 to 45 percent).

It is therefore impossible to conclude that “the protein-calorie ratio is one of the most fixed values of man's food behaviour” (12) or to claim that low or very high ratios are of short duration.

The Effect of Income

As money gains ground in the economy and per caput income rises, the choice of food widens and the diet structure undergoes changes. However, economic development cannot rapidly attenuate differences imposed in the pre-industrial stage by ecological and cultural factors on which the food patterns are based.

In agrarian civilizations, the diet's protein-calorie ratio depends, as we have seen, very strongly on the nature of the staple food (roots, tubers or cereals). However, the trend towards diversification shows no exception. It is quite usual to observe that, even at a very low income level, 25 to 40 percent of money expenditure on food serves to buy animal products so that their consumption grows strongly with income (6). For instance, the protein-calorie ratio in Madagascar, which is 9 percent for more than half of rural households, improves little by little and reaches 11 percent in classes with very high income (7). (Table 7)

In Tunisia, the protein calorie ratio tends to decline slightly in the lowest five classes of income, and to increase slowly in the highest classes, although the intake of animal protein shows a steady progression with income.

In the United Kingdom, the consumption of animal protein has reached levels which are quite independent from income (low income elasticity), while the protein calorie ratio is fairly constant around 11 percent and appears somewhat higher in the two highest income classes only.

Substitution animal products for plant products should markedly improve the protein calorie ratio of the diet, but this beneficial effect is lessened by a correlative increase in the consumption of fats (separated fats and unseparated animal fats) and of sugar, both of which provide calories without protein. It follows that the protein calorie ratio shows very limited responsiveness to changes in the structure of consumption and changes only very slowly.

In Greenland and Alaska (Table 6), in an environment that supplies exclusively animal products, the diet is being diversified by imported products generally with a high carbohydrate content, such as bread, rye, peas, sugar (Greenland) and cereal products, sugar, dairy products and fats (Alaska), whose protein calorie ratio is less than 9 percent. The traditional diet based on meat and fish, which in 1855 showed a high protein calorie ratio (43 percent), underwent diversification towards more carbohydrates with the development of a monetary economy, so that 80 years later, in 1935 – 43, the protein calorie ratio had dropped to 17.8 percent. It would therefore seem that more freedom in the choice of food has tended to lower the protein calorie ratio of the Eskimo diet, bringing it closer to that observed in diets mainly based on vegetal products.

These results still very fragmentary, might suggest that diets evolve toward a protein calorie ratio in the order of 11 – 13 percent, the motivation for change being the stronger as the diet differs from this value. A reason might be found, as Trémolières thought, in mechanisms of physiological regulation, for which there is however no evidence as yet. Another explanation might be a desire to break away from the extreme monotony of the traditional diet, induced by the palatability of new foods available in a market economy, not to mention the prestige often associated with novelty. In such circumstances, there is little chance that this ratio corresponds to a physiological optimum. If the choice is commanded by taste, and if taste is based on physical characteristics such as “crunchy”, “fatty”, “fried” and “sweet”, over which the food industry now exerts uncontrolled command, one can well fear that the housewife's basked upon leaving the self-service shop will in future be full of “junk foods”.

Conclusion

For populations living in subsistance economy, the pattern of consumption is strongly influenced by ecology. As a result, the protein calorie ratio of the diet depends on the nature of the staple food and, as in the staple foods themselves, it varies very widely (between 5 and 45 percent). In this respect the protein calorie ratio is a useful indicator of the purposes of dietary typology.

Economic development and rise in incomes by widening the choice of foods removes the constraints imposed on the diet by the environment and promotes changes in the structure of food consumption, viz. replacement of vegetal by animal proteins and of carbohydrates by fats. There is ample proof of this trend in diets with a strong vegetarian component, which are the majority, while an inverse trend seems to occur in populations such as hunters, fishermen and nomadic stock breeders, which are forced by ecological constraints, to consume mainly animal products.

The increase in consumption of animal products, which should markedly improve the protein calorie ratio, is strongly restricted by a correlative increase of fats and sugar which tends to deteriorate the protein calorie balance. It follows that this ratio shows high rigidity and turns out to be an indicator rather irresponsive to structural changes. Nevertheless, it cannot be denied that, under the impact of increases in income, this ratio is changing slowly and seems to tend toward values probably ranging between 11 and 13 percent. Is this a desirable nutritional optimum, attributable to mechanisms of physiological regulation, yet unexplained, or the result of a better satisfaction of tastes made possible by a wider choice of foods? For diets which have protein calorie ratio below or above these figures, the attainment of such values can be only a very long-term objective: indeed, various factors (ecology, high rate of population growth preventing or slowing down the rise in per caput income and the large numbers in the poor socio economic classes) are acting together in the same direction, so that the structure of the diet as reflected by the protein calorie ratio changes only very slowly.

REFERENCES

1. Trémolières, J. Physiologie de la nutrition appliquée à la médecine in Autret, M. et Ganzin, M. Nutrition alimentation tropicales, Tome II p. 1000, FAO Rome (1957). Leconte édit.

2. Trémolières, J. Les besoins nutritionnels de l'homme, Cah. ing. agr. 170, p. 18 (1962).

3. Widdowson, E.M. A study of individual children's diets, HMSO London (1947).

4. Périssé, J., Sizaret. F. & François, P. The effect of income on the structure of the diet, FAO Nutrition Newsletter 7, 3 (1969).

5. Sherman, H.C. Chemistry of food and nutrition, 5th ed., Macmillan Co. New York (1937).

6. Périssé, J. L'alimentation en Afrique intertropicale. Thesis No. 4436 Fac. Pharm. Univ. Paris (1966).

7. François, P. Budgets et alimentation des ménages ruraux à Madagascar en 1962, Tome 2, rapport-secret-état Aff. Etrangères chargé de la coopération, INSEE.

8. Sinclair, H.M. The diet of Canadian indians and eskimos, Proceed. Nutr. Soc. 12, 69 (1953).

9. Heller, C.A. & Scott, E.M. The Alaska dietary survey 1956–61, Rep. No. 999AH-2, U.S. Dept. Health Educ. Welfare.

10. Kamoun, A. et al. La nutrition des ménages en Tunisie 1965–67, rapport-secret-état Plan Finances, Tunis (1969).

11. Kamoun, A. et al. Enquête nationale sur le budget et la consommation des ménages 1975, rapport Institut National de la Statistique, Tunis (1978).

12. Trémolières, J. & Claudian, J. Apport des études de comportement à la compréhension des facteurs de l'appétit, Cah. nutr. diet., 1, 39–51 P.U.F. édit. Paris (1966).

13. Household Food Consumption and Expenditure - 1966, 1968. Annual Report of the National Food Survey Committee, H.S.M.O., London.