The Joint FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements1 took place in Rome from 5 to 17 October 1981. The Consultation was opened by Professor Nurul Islam, Assistant Director-General, Economic and Social Department, FAO. He welcomed the participants on behalf of the three agencies and emphasized the need for a re-examination of the requirements for energy and protein in the light of recent scientific developments.
More than ten years have elapsed since the Joint FAO/WHO Ad Hoc Expert Committee on Energy and Protein Requirements (1) met in 1971. That meeting was the first of its kind at which the requirements for energy and protein were considered together. In its terms of reference the Committee “was asked to examine the interrelationships between requirements for energy and proteins and to recommend means for the integration of requirement scales for energy and proteins, if that were feasible”. This was clearly an important step forward.
In its report (1), published in 1973, the 1971 Committee reviewed the principles on which some other groups of experts had based their recommendations on energy (2, 3) and on protein (4) requirements. It had been stated consistently that estimates of nutrient needs were concerned with groups and not with individuals. The 1971 Committee confirmed that assertion but emphasized two additional points: (a) that estimates of requirements are derived from individuals rather than groups, and (b) the nutrient requirements of comparable individuals often vary. The Committee further pointed out that requirement estimates can be related to individuals, but only on a probability basis; this concept is developed further in the present report.
1 A list of participants is given in Annex 10.
The first two FAO Committees on Calorie Requirements (2,3) established three general concepts:
In general, these concepts have stood the test of time.
Ideas on the assessment of protein requirements have progressed in a rather different way. The FAO Committee on Protein Requirements (4), which met in 1955, placed particular emphasis on the pattern of human amino acid requirements and the definition of requirements in terms of a reference protein with an “ideal” amino acid composition. Quantitative estimates of protein requirements were based on information available at that time on the needs for essential amino acids. In 1963 a Joint FAO/WHO Expert Group on Protein Requirements (5) introduced the new concept that the requirement for protein is determined by the rate of obligatory nitrogen loss from the body (principally in the urine, but also in faeces and through the skin) when the diet contains no protein. Measurement of these losses should provide an estimate of requirement, with correction for protein quality.
The 1971 Committee made advances in two directions. First, it recognized that even with protein of high biological value, the minimum nitrogen intake needed to ensure balance, which has generally been used as the criterion for the maintenance requirement, is larger than the so-called obligatory nitrogen loss. An attempt was made, in the light of the information available at the time, to determine the magnitude of this difference.
The second advance was the clear recognition that in estimating requirements for groups, the principles are not the same for energy as for protein. For energy, an individual's intake must match his output if he is to remain in a steady state, and it is accepted that physiological mechanisms exist by which this balance is normally maintained, albeit not each day. For protein, in contrast, there is no evidence of a regulatory mechanism that matches intake to requirement. However, there is also no reason to suppose that an intake moderately larger than the individual's physiological need will be harmful, at least within fairly wide limits. Together, these considerations led to an approach that described on the one hand an average requirement for energy and, on the other hand, a safe level of intake for protein. The safe level for a population was defined as the average protein requirement of the individuals in the population, plus 2 standard deviations (SD). There was little information about the variability of individual requirements, and the 1971 Committee accepted an estimate of 15% for the coefficient of variation.
In 1975 FAO and WHO convened an informal gathering of experts (6) to consider problems that had arisen in the application of the report of the 1971 Committee. They considered a number of situations in which it was thought that the 1973 report had been misused or was incomplete. They also recognized that the emphasis placed by previous groups of experts (2–4) on specifying nutrient requirements for healthy populations was an ideal. They began to tackle some of the problems that arise in reconciling this ideal with reality. Of particular importance are two questions relating to children: adjustments of requirements for deficits in growth and for the effects of frequent infections.
In 1978 a further informal meeting of experts continued the review process begun in 1975 (7). This group identified five main areas of uncertainty, particularly in relation to protein requirements.
Furthermore, the important question was raised of the practical relevance of the traditional criteria by which requirements are determined, i.e., nitrogen balance for protein and the maintenance of body weight for energy. The group pointed out that the gaps in knowledge that it had identified were all within the framework of traditional approaches to the problem of determining protein requirements. It raised the question whether adaptation to low protein intake involves any disadvantages, provided that the intake is sufficient to achieve balance and normal growth. Similarly, weight maintenance, the usual criterion of energy balance, takes no account of whether body weight is optimal, or whether the “requirement” allows for a socially adequate level of physical activity.
The 1978 group therefore concluded that a further full-scale expert consultation was necessary for two reasons: (a) enough new knowledge had accumulated since 1971 to justify trying to fill some of the gaps in the 1971 Committee's report; and (b) account had to be taken of the capacity of man to adapt to different nutritional and environmental conditions. The concept of adaptation is not easy to define, and it is even more difficult to determine the limits within which an adaptation may be regarded as successful. Moreover, if it is accepted that as a result of adaptation requirements may differ in different situations, it may be inappropriate to aim for uniform international standards. It was therefore necessary to re-examine the concepts on which requirements are estimated and, as far as possible, to relate them to the functional capacity both physical and mental, of the individual in a particular society—in other words, to ensure that the requirements relate to the actual conditions of life.
It follows from this line of thought that throughout the process of determining protein and energy requirements the question “requirements for what?” has to be borne in mind. Acceptance of this view demands a closer liaison between biologists, who are concerned with the physiological basis for estimating requirements, and social scientists, who are concerned with the practical application of those estimates.
Ideally, a group set up to advise on requirements should include representatives of a wide range of disciplines. However, this was not considered to be feasible at the present time. As the 1978 report (7) shows, in spite of all the previous work that had been done, many difficult biological and statistical problems remained, and it was necessary to tackle these first. The work of the present Consultation should perhaps be regarded as preparatory to a more completely integrated approach in the future. The present report does, however, identify some of the principles that should be considered when applying estimated requirements. Unlike the report of the 1971 Committee, this report does not include detailed recommendations on application of the estimates at the national level.
The primary task of these committees or other expert groups (1, 6, 7) has been to provide the United Nations agencies with tools for addressing practical questions, such as assessment of the adequacy of food supplies and targets for food and nutrition policy. Past reports have also influenced the decisions of national committees in developing estimates of requirements appropriate to local conditions and applications.
At the same time, the international meetings of experts have been extremely productive in generating new ideas and stimulating new research. This is particularly apparent in relation to protein requirements; each successive meeting, building on the work of its predecessors, has identified gaps in current knowledge which research workers in many countries have done their best to fill. The identification of problems and the stimulation of further research is an extremely important function.
There is a widespread view that the limiting factor in the solution of the world's nutritional problems is not the lack of knowledge but the inadequacy and maldistribution of resources. The reports of the expert meetings over the years make it very clear that this conclusion is not entirely justified. Resources are indeed limited, but to use them as efficiently as possible requires a sound basis of knowledge. For this reason the present report, like its predecessors, ends with a section on the needs for future research.
One of the clearest indications of the need for continuing research is the fact that the recommendations of each successive meeting, including the present one, differ in some respects from those of its predecessors. Each meeting, moreover, tends to emphasize different aspects of the problem. The report of the 1971 Committee included, in its introduction, an historical account illustrating the evolution of ideas and knowledge. These changing ideas may cause problems for planners and policy-makers, but it has to be accepted that we can only approach our aim by a process of successive approximations.
Because of advances in our knowledge during the past decade, it is inevitable that the recommendations in this report should differ in some important respects from those of the 1971 Committee. That committee built up its estimates of energy requirements on the basis of a reference man and woman who were “arbitrarily selected convenient starting points for extrapolation … and … not intended to suggest ideal standards. They were originally chosen as being representative of groups of men and women whose food consumption and energy expenditure had been carefully studied” (l, p. 23). In the present report there is some change of emphasis. The concept of the reference man or woman seems to be unduly restrictive once it is recognized that in the world as a whole there is a wide range in both body size and patterns of physical activity. The object of the tables in this report is to reflect this wide range, so that the user can choose the values that are most appropriate to his or her conditions.
As a matter of principle we believe that estimates of energy requirements should, as far as possible, be based on estimates of energy expenditure, whether actual or desirable (see section 4). To determine requirements from observed intakes is largely a circular argument, since in both developing and developed countries actual intakes are not necessarily those that maintain a desirable body weight or optimal levels of physical activity, and hence health in its broadest sense. However, it has not been possible to follow this principle in the case of children, because we do not have enough information about their energy expenditure. We have attempted to give some detailed examples of divers patterns of physical activity in different age and sex groups in the hope that they may provide useful guidelines for the application of requirement estimates.
In formulating requirements for protein we have followed the 1971 Committee in trying to establish two reference points where knowledge may be regarded as reasonably reliable. The first is the maintenance protein requirement of the young child; the second is the requirement of the young male adult—a group that has been studied intensively in the last 10 years (see section 6). We still, however, have much less direct information than is desirable about other age groups. It has therefore been necessary, as in previous reports, to make indirect estimates of their protein needs by interpolation. In addition, previous meetings have emphasized the need to correct the estimated protein requirement for differences in protein quality. The present Consultation concludes that few natural diets provide insufficient amounts of essential amino acids, except for infants and preschool children. On the other hand, it is apparent that more attention should be given to the digestibility of the proteins in a mixed diet, especially in the diets of people in developing countries. As pointed out by the 1975 informal gathering of experts (6), this subject was relatively neglected by the 1971 Committee, but it is clear that the availability of dietary protein for all age groups can be significantly affected by digestibility, and that protein requirements should be appropriately adjusted for increased faecal losses of nitrogen.
The Consultation was conscious of the responsibility involved in proposing these changes, which may well have important implications for planners. Since the knowledge available was seldom adequate for strict conclusions, the Consultation had to base its estimates on its judgement of the scientific evidence available together with past experience. The conclusions of the Consultation are as well grounded as is possible given the present state of knowledge. Future experience will show how realistic they are.