Changing concepts stimulate new needs for research. The stand that was taken by the present Consultation, that the aim should be to define requirements for health, implies that almost every aspect of human health and function is potentially relevant. However, since resources are limited it is unproductive either to outline research needs too broadly or to attempt to include every possible topic that might have a bearing on the problem. To be useful, it is necessary to judge the priorities.
In defining research priorities, subjects have been placed into two groups distinguished by the nature of the questions and the disciplines and facilities needed for answering them.
The first group consists of those biological questions that need to be answered most urgently to provide better numerical estimates of human requirements. The second group includes epidemiological studies aimed at testing the validity of the estimates in populations under different environmental and social conditions, relying on more general, and indeed more realistic, criteria of health and function than those that are used in metabolic investigations. This second group also includes questions that relate to the use of the requirement estimates by planners and policy-makers. Since only the general principles of application have been considered in this report, the research needs described under this heading are necessarily few and incomplete. They will surely be expanded as future users attempt to translate the principles into practice.
A. Biological questions
Problems common to both energy and protein requirements
(1) Attention has been drawn many times in this report to the variations between individuals regarding their requirements for both energy and protein. This variability is of great importance for the practical application of requirement estimates (section 11), and better data are needed. The allowances that should be made for it, in judging the capacity of different diets to fulfil requirements, depend on an improved understanding of the genetic and metabolic causes of individual variability. In particular, the extent, if any, to which individual needs for protein and energy are correlated must be known. A certain amount is known about the magnitude of variability between individuals; much less about the variability of requirements in the same individual at different points in time.
(2) Related to this question, more information is urgently needed on the extent of day-to-day variations in weight gain of young children, the reasons for these variations, and the effect they may have on energy and protein requirements.
(3) There is one section of the population—pregnant and lactating women—whose intakes of both energy and protein very often appear to be far less than the amounts recommended not only by this Consultation but by all previous committees. Do adjustments occur that have not so far been identified? If they do occur, what is the cost to the mother and infant, before and after birth? These questions are of great scientific and public health importance.
(4) An attempt has been made in this report to estimate the extent to which frequent infection increases the energy and protein requirements of children. These estimates are based on rather fragmentary evidence. This subject needs to be explored in depth, both at the metabolic and community level.
(5) A high priority should be given to the development of improved methods for measuring energy expenditure over relatively long periods. Such methods would allow many of the problems mentioned below to be solved.
(6) More information is needed on the extent to which the energy cost of a given task, expressed as a multiple of the BMR, is affected by age, sex, and body weight. Such studies should include both static and dynamic types of activity, and activities that may be affected in different ways by body weight, e.g., comparisons of lifting the body with lifting an external object.
(7) If estimates of energy requirements are to have wide validity, they must take account of the extent to which the body can adapt to different levels of intake by a change in either basal metabolic rate or in the efficiency of physical work. This is a major field for future research.
(8) An allied question is whether observed differences in metabolic rate between different populations and groups result from ethnic factors, climate, or adaptation. More studies are therefore needed on different groups living under different environmental conditions.
(9) In the last few years there has been increasing emphasis on the role of dietary fibre in the maintenance of health, and diets rich in fibre are being widely advocated. As a consequence, there is a need for more research on the availability of energy in such diets.
(10) Low energy density, bulkiness, and glutinous consistency are characteristics of diets given to children in many parts of the world, making it difficult for their energy requirements to be fulfilled. There is a promising field for research on simple methods of improving these diets, which can be applied at the village level.
(11) The protein requirements for growth in young children still present unsolved problems of considerable importance. As mentioned above (question (2)) it is not clear how far day-to-day variability in growth rate affects protein needs. Secondly, the widespread prevalence of stunting in linear growth raises the question whether the protein requirements for growth in height may be greater than those for weight gain, which has hitherto been regarded as an adequate criterion.
(12) Although in recent years there has been increasing interest in measurements of the state of protein nutrition in adults as well as in children, there are still few, if any, objective biochemical indices of marginal protein malnutrition. It is important to continue the search for such methods as a means of checking the validity of requirement estimates, and helping to determine the prevalence of protein deficiency states.
(13) The main criterion of protein requirement that has been used by this Consultation, as by the 1971 Committee (1), is nitrogen balance; the shortcomings of the method have already been discussed (section 5). A series of important problems emerges from this discussion: the extent to which adaptation in urinary nitrogen output can occur in the long-term, whether such an adaptation can be achieved without a significant reduction in lean body mass, and whether such a reduction, if it occurs, carries with it any functional impairment.
(14) The usefulness of other criteria, such as measurements of total body nitrogen and potassium, needs to be further explored in centres that are equipped to do so.
(15) As discussed in this report (section 7), the digestibility of protein may have a much more important effect on protein quality, at least for adults, than the amount or pattern of essential amino acids. More work is therefore needed on the digestibility of proteins, particularly under different environmental conditions, e.g., in populations with a heavy load of infection and infestation of the gastrointestinal tract.
(16) At the same time, there is scope for further research on amino acid requirements, particularly of those groups, e.g., adolescents, about which little is known.
B. Epidemiological and community studies
(17) Energy and protein requirements have been defined in this report as the amounts needed to maintain normal or acceptable health and function. This definition is unavoidably imprecise. Our theoretical estimates need to be tested in the field in programmes designed to examine the relationships between habitual intakes and defined functions such as growth, reproductive performance, work output, resistance to infection, mental development, etc. It is appreciated that such studies are difficult, laborious, and expensive, because of the need for long-term observations and the control of confounding variables.
(18) Epidemiological research of this kind can be made more effective in two ways: by comparisons between different groups with different intakes, and by observing the effects of interventions. Such research, which has already been undertaken or is in progress in a number of centres, should be actively encouraged.
(19) This report has particularly emphasized the need to take account of “discretionary” activity (section 4), and the importance of a minimal level of physical activity for the maintenance of health and wellbeing. It follows that there is a real need for descriptive profiles of activity and energy expenditure. Have cultural practices and patterns of activity evolved to maintain energy balance in the face of chronically limited intake? Does an increase in food intake lead in practice to an increase in physically or socially desirable activity? How long does it take before a food demand is reflected by a change in activity profiles? Such studies will require the cooperation of other disciplines, for example, behavioural scientists.
(20) This report has also shown very clearly the inadequacy of our knowledge of the protein and energy requirements for catch-up growth, and for resistance to and recovery from infections under the conditions that prevail in many communities. This is a priority subject for further research.
(21) Under the general heading of epidemiological research, a particular problem that remains unsolved is the relationship between dietary intakes of protein and energy and the development in the individual and the prevalence in the community of different forms of protein-energy malnutrition. There is no general agreement about the etiology of the kwashiorkor syndrome, and it would be of practical importance to settle the question, whether or not it represents an imbalance between protein and energy intakes.
(22) All community studies aimed at testing the validity of requirement estimates must involve measurements of the food intake of individuals in relation to their functional performance. It is therefore necessary to devise better methods of determining food intake, particularly habitual intake.
(23) Since for planning purposes the family often has to be taken as the unit, more information is needed about the distribution of food within the family and the factors that affect it in different cultures. This is another example of the usefulness of “profiles” or case studies.
(24) It has been proposed (2) that a cut-off point (an energy intake less than 1.2 × BMR) could be used to identify individuals whose energy requirements are clearly not being met. It is a question for operational research whether a cut-off point of this kind is useful for planning purposes. If it is useful, then more work will be needed to identify the appropriate values of the cut-off point for different groups of the population.
Many of the subjects that were considered important in the past are not included in this summary of needs for future research, and it is likely that priorities will change during the next 10 years. Nevertheless, the Consultation emphasized that there will be a continuing need for both metabolic and community studies if health for all by the year 2000 is to include nutritional wellbeing.