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B. Report on the informal gathering of investigators to review the collaborative research programme on protein requirements and energy intake

Rome, 16-18 January 1980

Foreword
1. Introduction
2. Methods and results
3. Discussion
4. Future work
References

Foreword

The informal gathering described in this report was convened to enable the participating institutions to discuss the initial results from a collaborative research programme on protein and energy requirements, funded by DANIDA.

Differences and similarities of the research findings were noted and discussed. These findings will influence and shape the research protocol of this programme over the next year. The results described in this report and the results expected from the research during this next year should contribute greatly to knowledge on the interrelationships of protein requirements and energy intake. For this reason FAO and WHO feel this gathering was timely and useful.

Prof. J.C. Waterlow chaired the meeting and wrote the subsequent report. FAO and WHO wish to express their appreciation of his adroit summarizing of the various points of view expressed by the participants and succinct descriptions of the salient points and conclusions incorporated in this report.

1. Introduction

In 1977 a collaborative programme of research on protein and energy requirements was established, funded by DANIDA* and administered by FAO. Representatives of four scientific groups (INCAP, Guatemala; Mahidol University, Thailand; the National Institute of Nutrition, Hyderabad, India; the Tropical Metabolism Research Unit, University of the West Indies, Jamaica) met in Rome in October 1977, with outside consultants and staff members of FAO and WHO, to draw up a research plan. The conclusions reached at that consultation were summarized in the Report of the First Joint FAO/WHO Expert Consultation on Energy Intake and Protein Requirements (1). The present report described a follow-up meeting held in Rome in January 1980 to discuss the results of the research obtained and to consider future extensions of the work. The participants are listed at the end of the report. The Indian group was not represented, having withdrawn from the programme.

At the meeting it was agreed that there were two priority questions that should be tackled first:

1. Is the present "safe level" of protein intake adequate: (a) at habitual levels of energy intake; and (b) at levels of energy intake that correspond with present estimates of energy requirements?

2. Would habitual protein intakes be adequate if energy intakes correspond to present estimates of energy requirements?

The first question was examined by the Thai group, who worked on both children and adults. A study of this question had already been made by INCAP under a separate grant from WHO and the United Nations University (UNU). Results of that investigation, referred to in this report as INCAP study 1, are included because they are important for comparison with the results obtained in Thailand.

2. Methods and results

2.1. Adequacy of the "Safe Level" of Protein at Habitual Energy Intakes

This question was addressed by studies at three levels of energy intake, with fixed intake of protein calculated to be as close as possible to the "safe level."

2.1 .1. Studies on Children

2.1.1.1. Thai study: Some of the conditions of the Thai study are summarized in table 1. The subjects were nine children who had recovered from malnutrition, were normal weight for height but underheight for age. The duration of the study period was a relatively short period (11 days), and none of the children was over three years of age.

The diet corresponded as far as possible with that habitually eaten. It was designed to be fed at constant protein intake, but at three different levels of net energy intake (table 2).

In preparing the experimental diets the energy values of foods were taken from the Food Composition Table for Use in East Asia (2). When the figures for the gross energy content of the diets measured by bomb calorimetry became available, some adjustments were made by adding a little more fat or sugar, to reach the energy levels specified. Faecal energy losses were also measured, so that the net energy intakes were known precisely.

TABLE 1. Some Features of the Design of Studies on Energy Intake and Protein Requirements in Children

TABLE 2. Studies in Children: Protein and Energy Intakes Compared with Safe Levels of Protein and Estimated Energy Requirements

a. In terms of milk protein.
b. From FAD/WHO (3), table 23, mean of 1-4 years
c. Assumed for milk or egg. d. From FAO/WHO (3). table 8.

The amounts of the main dietary components were adjusted so that the "safe level" of protein intake was reached after calculated corrections had been made for digestibility and protein quality. The digestibility was rather low - about 6~70 per cent; the actual amount of absorbed N was very close to that recommended as the "safe level" (table 2).

Finally, some additions were made of vitamins and minerals. The diets therefore closely resembled habitual diets, but did not match them exactly. That would have been impossible, given the experimental design.

The protein and energy intakes of the Thai study are shown in table 2. The observed protein intake is comparable with the "safe level" when corrected for digestibility. It is clear that the objective of the experimental design to match the protein intake from Table 2 also compared the gross and net energy intakes with the requirement. The actual intakes were measured directly by bomb calorimetry. The estimated energy requirement given by FAO/WHO in 1971 (3) of 101 kcal/kg/day for children of one to three years is mid-way between the net energy intakes A and B, and considerably higher than C. However, problems arise in comparing these energy intakes with requirements, because the values are not derived in the same way. This question will be considered in more detail in the discussion (section 3.3.3).

Nitrogen balances and rates of growth at the three levels of energy intake are shown in table 3. At level A (net intake 109 kcal/kg/day), the Thai children showed excellent growth and substantial nitrogen retention. At level B (93 kcal/kg/day) the children gained weight at 1-2 g/kp/day and retained on average over 60 mg N/kg/day. Both weight gain and N retention were somewhat greater than would be expected in normal children of this age, so that some catch-up may have been occurring. At energy level C (80 kcal/kg/day), growth was no longer adequate, but nitrogen balances were still positive.

2.1.1.2. INCAP study 1: In addition to the work of the Thai group described above, sponsored by DANIDA, INCAP conducted a very similar study. which was sponsored by WHO and UNU. This is referred to as INCAP study 1. It is useful to compare the results of the two studies. The conditions of the INCAP study 1 (see table 1 ) were similar to those of the Thai study except that each dietary period was of longer duration (40 as against 11 days); the subjects were slightly older; they had been fully recovered from malnutrition for at least one month; activity was maintained, and the energy intakes were slightly lower, as is appropriate for older children.

TABLE 3. Weight Gains and Nitrogen Retention at Various Levels of Net Energy Intake

a Corrected for assumed skin loss of 5 mg/kg/day

The protein intake in INCAP study 1, corrected for digestibility, closely matched the theoretical safe level (table 2). The longer duration of the study allows a better estimate of the capacity of the diet to promote catch-up growth. and hence more confidence in assessing whether the theoretical safe level is indeed adequate. The energy intakes are also shown in table 2. As in the Thai study, they were measured by bomb calorimetry.

Comparison of the results of the two studies reveals some important differences (table 3). At energy intake C (80 kcal/kg/day), both growth and N retention fell off in the Thai children but not in those at INCAP. The reason for the difference may be that the former were somewhat younger. At the lowest energy intake (71 kcal/kg/day), the growth of the INCAP children became inadequate, but the positive N balance remained unchanged.

In the INCAP study estimates were made of energy expenditure and hence of energy balance. At all three levels of intake the children, on average, were in balance. At level C (80 kcal/kg/day), weight gain was maintained but expenditure was reduced. At level D there was no further fall in expenditure. Evidently energy expenditure was conserved at the expense of decreased weight gain.

2.2.2.3. Conclusion: These results seem to show clearly that, at a net energy intake of about 90 kcal/day, the "safe level" of protein, corrected for digestibility, is on average adequate for growth and nitrogen retention. The criteria of adequacy will be considered in more detail in the discussion (section 3.1.4). Although at a lower energy intake (level C), both N balance and growth were still satisfactory in the INCAP children, this cannot be assumed to be an acceptable state of affairs, since energy expenditure was reduced. The relationship of these findings to estimates of energy requirements is discussed in section 3.1.1.

The two studies provide an answer to the first part of question 1 (a). whether the "safe level" of protein would be adequate at habitual levels of energy intake. In the case of Thai pre-school children, surveys indicate that the habitual energy intake is about 80 per cent of that recommended by FAO/WHO in 1971 (3), i.e. about 80 kcal/kg/day. In Guatemala the habitual intake of pre-school children is said to be about 75 kcal/kg/day. These values have been calculated from dietary surveys by applying the usual Atwater factors. It is possible that they may overestimate the true net energy intake (see section 3.1.1). In any case, it seems clear from table 3 that intakes of this order, which fall between levels C and D, will not maintain adequate growth. It is also probable from the INCAP results that they will be insufficient for desirable levels of physical activity.

2.1.2. Studies on Adults

The Thai workers also made a study on adults who were given the "safe level" of protein at five different levels of energy (gross intake 36-55 or net intake 34-53 kcal/kg/day). The protein intake was fixed at 0.72 g/kg/day, derived from rice and fish in the ratio 80:20, with an amino acid score of 87 and an assumed digestibility of 90 per cent.

On average, the subjects lost weight at the rate of 0.7-1 kg over a period of 10 days at all levels of energy intake. This result is difficult to explain. Energy expenditure was estimated by recording activities throughout the day; it was virtually the same, at 43 45 kcal/kg/day. regardless of the energy intake. The mean energy loss in the stools was 5 per cent of the intake. Thus, on average, the subjects should have been in positive energy balance on net intakes of 53 and 48 kcal/kg/day, and they should have been more or less in equilibrium on 43 kcal/kg/day, which corresponds to the estimate of average energy requirement. At the three higher energy intakes (43, 48, and 53 net kcal/kg/day) the mean N balance, corrected for skin losses, was -2 mg N/kg/day, which is not significantly different from zero. At the two lower energy intakes (34 and 38 net kcal/kg/day), the N balances were negative (-28 and 18 mg N/kg/day). To correspond with the weight loss the N balances should have been even more negative, of the order of -40 to -60 mg N/kg/day. There is, therefore, a discrepancy between weight loss and N balance, and this discrepancy has not been resolved. These findings suggest that nitrogen balance is not a sensitive indicator of the adequacy of energy intake, and are in agreement with the results at the lowest energy level (D) in INCAP study 1 (table 3). Until an explanation has been found for the weight loss. no firm conclusions can be drawn about the adequacy of the protein intake. From the balance data alone, it would appear that the "safe level" of protein was adequate when the net energy intake was equal to or greater than the estimated requirement.

2.2. Adequacy of the Habitual Protein Intake When Energy Intake Corresponds to the Requirement

This question was addressed by the INCAP group in another study in children (INCAP study 11, sponsored by DANIDA). Each child was observed for a minimum of 56 days with measurements of nitrogen balance on every fourth day. A diet based on the habitual dietary pattern of Guatemalan children was fed ad libitum. but the energy intake was adjusted, by varying the amounts of oil and sugar, to approximately 92 kcal/kg/day {gross). This corresponds to 8385 net kcal/kg/day, which is higher than the habitual intake (see previous section), but lower than the estimated energy requirement of children of this age. The children were encouraged to be physically active, and restraint for urine collections was kept to a minimum. Energy expenditure during the day was estimated by the calibrated heart-rate method, and by night from the BMR. On this regime the children had an average positive energy balance of 9 kcal/kg/day. The average protein intake was 1.85 g/kg/day, with a coefficient of variation of only 12 per cent. The apparent digestibility of the protein was 72 per cent and the true digestibility 79 per cent.

The average weight gain was 0.6 g/kp/day, with a large range of variation among individuals. This is about the rate expected in children of this age. Most of the children, initially somewhat stunted (average 86 per cent of standard height for age), showed some degree of catch-up in height. In general, therefore. growth on this regime appears to be satisfactory. On average, the children had a positive N balance of 85 + 22 mg N/kg/day. This is slightly larger than the N retention found in the previous study at similar energy intake, although the rate of weight gain is less. Here again there is a dissociation between N balance and weight gain. The reason for this difference in N retention may be that in the previous study the protein was all from vegetable sources. In study 11 the digestibility was better, so that net protein intake averaged 1.33 g/kg/day compared with 1.03 in study I.

Some children developed an infection in the course of the study. This produced transient decreases in food intake and weight gain, compensated by increases later, so that there was no effect on N balance or growth in the long term.

INCAP study II differed from classical balance studies in its duration and in the provision of a mixed diet fed ad libitum. It is concluded, first, that a net energy intake of 83-85 kcal/kg/day, which is somewhat lower than the estimated requirement, satisfies the energy need of children aged two to four years; second, that at this energy level the habitual protein intake, which is a little larger than the "safe intake," is adequate, as judged both by N balance and by growth. In fact. these intakes allowed for catch-up after minor intercurrent infections.

2.3. Measurements of Protein Turnover

The Jamaica group has been trying to develop the measurement of protein turnover as a dynamic indicator of the adequacy of protein intake. The theory behind this undertaking is that growth involves an increase in the rate of protein turnover above that required for net synthesis (4, 5). Second, and most importantly in the present context, protein turnover is a process that requires substantial amounts of energy. Therefore, if the energy supply is limiting, an immediate effect may be expected on the rate of protein turnover, as has been shown in animal experiments. It is known, moreover, that the turnover rate responds very rapidly, in a matter of hours, to changes in food intake.

If these assumptions are correct, measurements of protein turnover at one point in time should provide a more rapid estimate of the adequacy of protein and energy intakes than that derived from observations of growth, and more accurate (and possibly simpler) than that derived from studies of N balance. Although the techniques are still in their infancy. the Jamaica group has made some progress in tackling the methodological problems, in spite of delays caused by technical difficulties.

3. Discussion

3.1. Problems of Experimental Design and Interpretation

3.1.1. Determination of Energy Intakes

The results of these studies illustrate a difficulty that arises in planning energy intakes and relating them to requirements. For example, in INCAP study I the planned intake at energy level. A was 100 kcal/kg/day, which is equal to the estimated energy requirement of children at one to three years (3). The amount of food needed to provide this intake was calculated from the composition of the diet by applying the Atwater factors. The gross intake, measured by bomb calorimetry, was 99 kcal/kg/day. Similarly, at the other levels of energy intake, the gross intakes and the planned intakes were the same, but the net intakes were some 10 per cent less. Presumably the reason for this is that the digestibility of both protein and carbohydrate in the diet was lower than that assumed in the calculation of the conventional Atwater factors. This is not a new observation (cf. 6). but it is important to realize the extent of the discrepancy that may arise.

Although the report of the FAO/WHO 1971 meeting does not say so directly, it must be presumed that the estimates of requirements represent net intakes based on the Atwater factors, i.e. on the assumption that 95 per cent of ingested protein and 99 per cent of ingested carbohydrate are available as sources of energy (3, annex 2). If that is so, the results of these studies suggest that the recommendation for this age group is too high. The recommended intake (assumed to be net) is 101 kcal/kg/day and the observed net intake, which was considered to be adequate, was 90 kcal/kg/day.

3.1.2. Determination of Level of Protein to be Fed

Since one of the main purposes of these studies is to find out whether the "safe level" is adequate under various conditions, the first problem in the design is to decide how much protein represents the "safe level." Several difficulties become apparent.

1. The children who acted as test subjects were, in general, stunted, though of normal weight for height. Both the INCAP and Thai groups decided that the amount of protein provided should be based on biological age (i.e. height age) rather than on chronological age. This immediately introduced a departure from strictly "normal" conditions, and allowed some margin, albeit small, for catch-up. It has been suggested that stunted children may utilize protein more efficiently than so-called "normal" children, so that tests made on them will underestimate the true "safe level." Such an argument, however, is academic. A very large proportion of children in developing countries are stunted, and it is the requirements of the children in these countries that we are interested in.

2. When the protein is derived from the habitual diet, it is necessary, in determining the amount to be fed, to correct for digestibility and protein quality. In both studies the observed digestibility turned out to be lower than had been expected. It is satisfactory that in spite of this, the "safe level" proved to adequate by the criteria adopted in this report (see below). The observed net protein utilization was lower than that based on the chemical score. This simply means that more N was being absorbed than was strictly necessary for growth and maintenance. It would not be correct to argue from this that the "safe level" of protein supplied was miscalculated. The definition of "safe level" is an operational one, and it is part of this definition, as proposed by FAO/WHO (3), that the correction for protein quality should be based on amino acid score. It was therefore proper to follow this procedure, which in practice seems to work, because it produces an estimate of "safe level" that in fact is safe.

3.1.3. Modifications of the Habitual Diet

In these studies vitamin and mineral supplements were added to ensure that the only limiting factors would be protein or energy. Further consideration will have to be given to the advisability of doing this in future studies, which will be more and more concerned with reproducing natural conditions. For example, it was pointed out that, in diets based on cereals and legumes, zinc deficiency may be a factor limiting growth. The routine addition of supplementary zinc would preclude the possibility of finding out whether or not this element is really limiting.

3. 1.4. Criteria of the Adequacy of Protein Intake

3. 1.4.1 . Weight gain For a test diet to be considered adequate, it is necessary for pre-school children to be gaining weight. However, as is widely recognized, weight gain is an insensitive and non-specific criterion.

3.1.4.2. Nitrogen retention: In these studies larger amounts of N were retained, after correction for skin losses, than would be accounted for by the weight gained. Similarly, the adults in the Thai study were seemingly in N equilibrium at the higher levels of energy intake although they were losing weight. These results are examples of a difficulty that has been encountered by many workers over the past half century: often more N is apparently retained than can be accounted for by any physiological process (7, 8, 9).

The question then arises: How large must the positive N balance be for the intake to be considered adequate? According to FAO/WHO (3), for pre-school children there should be retention of 70 mg N/kg/day, but no justification is given for the choice of this figure, although it is stated that "it may be too high." By this criterion almost all the retentions found in the present studies would be inadequate: for example, the average retention of 60 mg N/kg/day in INCAP study 1 at the higher levels of energy intake.

The expected N balance based on the normal rate of weight gain at two years would be 15-20 mg N/kg/day. In determining the criterion of adequacy, should this be increased by some arbitrary amount to allow for unexplained sources of loss? The question will need to be reconsidered by FAO/WHO. In the meantime, common sense suggests that retention of 40-60 mg N/kg/day must be considered adequate when, as in the present studies, the work has been so very carefully done that errors in collection and analysis may be regarded as minimal.

3.1.4.3. Other biochemical measurements: In the course of these studies measurements were made of haemoglobin, total serum proteins, albumin, and amino transferase as a check on changes in nutritional status. No useful information emerged. For example, there were no changes that could be correlated with decreasing N balance at lower energy intakes. However, it was thought worthwhile in future studies to examine the use of tests that may be more sensitive, e.g., of transferrin, retinol-binding protein, etc.

3.1.5. Variability of Nitrogen Retention

There is inevitably a range of variation in N retention on any one regime. In the Thai study in children, the coefficient of variation was about 10 per cent; in the two INCAP studies it was about 20 per cent. In the second INCAP study, in which the subjects were fed ad libitum, some children had net protein intakes as low as 1 g/kg/day, compared with the average of 1.33, and yet showed satisfactory nitrogen retention and growth. Thus, one cannot attribute all the variation in N balance to differences in intakes.

No formal analysis of variance has been presented, but inspection of the data suggests that the variability of balance was at least as great within as between children. The question then arises: Does the concept of "safe level" require that "practically all" (i.e. 97.5 per cent) of balances should meet the given criteria? It seems reasonable to suggest that, for any individual, when repeated balances are being measured over a period of time, it is necessary that the average N retention should be adequate. Unless the studies are made under very rigidly controlled conditions, which partly defeats their object, there will be some dayto-day fluctuations in intake, just as there are fluctuations in growth, as pointed out by the UNU Working Group (10). However, when dealing with a group, if the protein intake is to meet the safe level, the average N balance should be satisfactory in practically all members of the group. In all the studies reported here, the protein intake does in fact satisfy this criterion. For example, the lowest N retention for any group is that of the Thai children on a net energy intake of 80 kcal/kg/day. In this group the mean retention was 44 + 7 mg N/kg/day, which is still greater than the value proposed above (section 3.1.4) for the desired amount of N to be retained by children of this age.

In general, the present results suggest that the estimate made by FAO/WHO (3) was realistic in assessing the coefficient of variation of N balance between individuals at 15 per cent.

3.2. Energy Requirements

The report of the group that met in 1977 (1) emphasized the difficulty of determining energy requirements. The present studies have exploited to the full the available methods of measurement. Accurate information on net energy intake was obtained by bomb calorimetry of foods and stools. It is interesting that the faecal losses of energy were much lower than those of nitrogen.

There are three possible criteria for energy requirement: weight gain, nitrogen balance, and physical activity. Weight gain has obvious limitations in short-term studies. It was suggested by the Expert Group in 1977 that N balance might be the most sensitive measure of energy requirement. This was not borne out in either of the INCAP studies or in the Thai study on adults. On the other hand, in the Thai study on children, there was a correlation between energy intake and N retention, such that 1 mg N was retained per additional kcal ingested. This value agrees well with others reported in the literature. However, the relationship must be subject to some uncertainty, since the correlation coefficient is low (0.5) and the intercept give zero N balance at the impossibly low intake of 33 kcal/kg/day. A similar regression of weight gain on energy intake gives zero weight gain at a gross intake of 92 kcal/kg/day- a much more acceptable figure (11).

The reason for the discrepancy between the INCAP and Thai studies remains to be determined. One may speculate that the longer duration of the dietary periods in INCAP study I allowed for better adaptation to low energy intakes. It may be legitimate to conclude that the use of N balance as a criterion of the adequacy of energy intake does not seem very promising for practical purposes because it is too indirect and subject to too many uncertainties. Satisfactory N balance is a necessary criterion, but not a sufficient one, of the adequacy of energy supply.

In the INCAP studies, estimates of energy expenditure were made from the resting metabolic rate during the night and by the integrated heart-rate method during the day. In the Thai study on adults, energy expenditure was computed from a diary of activities. These measurements are important because they provide independent evidence of whether or not a given level of energy intake was adequate. For example, in INCAP study I a reduction in net intake from 87 to 80 kcal/kg/day was accompanied by a fail in energy expenditure without change in N balance, weight gain. or observed physical activity. This implies that measurement of energy expenditure may be the most sensitive indicator of the fulfilment of energy needs.

If the three criteria are applied to the present results, it appears that net intake of about 90 kcal/kg/day is adequate for children aged two to four years. The next level, a net intake of 80 kcal/kg/day, could be marginal, since energy expenditure was reduced in one study and N balance in the other. Lower energy intakes are clearly inadequate. No conclusions can be drawn from the Thai study on adults because of weight loss at all levels of intake.

It should be noted that, in order to bring the energy intake of the children up to requirement, it was necessary to supplement the habitual diet with oil or sugar. It seems clear that in both these diets, because of their bulk and low-energy density, the limiting factor for children is the intake of energy and not the concentration of protein.

4. Future work

4.1. Now Proposals

Draft proposals for further work were discussed. They will be modified in the light of the discussions and resubmitted. Briefly, the plans are as follows.

The INCAP group proposes another long-term study (90 days) on children who are considered to be adapted to marginal malnutrition. The study will be continued even if infections intervene. The habitual diet will be fed ad libitum. modified with oil to provide about 90 kcal/kg/day. No vitamin or mineral supplements will be given. Nitrogen balance measurements may be made at intervals if considered necessary. Energy expenditure and physical activity will be quantified. In view of the discrepancies in the literature, some biochemical indicators may be evaluated, such as transferrin and retinol-binding protein.

The aim of the study is to find out whether the habitual diet can promote catch-up growth provided that energy needs are met. The main problem foreseen is the accurate measurement of food intake unless the studies are done in a metabolic ward; this, however, would decrease the load of infection expected in the home environment.

The Thai group will make a further study on children for six months. The habitual diet will be fed ad libitum to give a hoped-for intake of 1.7 9 protein and 100 kcal/kg/day. Nitrogen balances will be measured at monthly intervals.

Although these studies will be done in a metabolic ward, they will approximate the conditions of actual life. The main criterion will be growth in weight and height. In effect, therefore, these are feeding trials under very well-controlled conditions.

In adults the Thai workers are measuring food intake to determine the cause of the weight loss at the higher levels of energy intake. It was felt that more metabolic studies would be premature until the cause of the weight loss was understood, and conditions were found under which it did not occur.

The Jamaica group will study protein turnover at maintenance levels of protein and energy, and also at intakes comparable to those being used by the other groups. The aim is to determine the changes that occur in rates of protein synthesis and breakdown at the time when adaptation is being stimulated. This work will be done on children who have regained normal weight-for-height after malnutrition. At this stage there is still a deficit in muscle mass, counterbalanced by a small excess in adipose tissue.

4.2. General Points Relating to Future Studies

4.2.1 . Duration of Studies

Stress was laid on the importance of long-term studies that will allow a better evaluation of catch-up growth, of mechanisms of adaptation, and of the responses to infection.

4.2.2. Energy Intake and Expenditure

The long-term studies on children will allow observations of individual variations in ad libitum energy intakes and there will be an opportunity for investigating the factors associated with these differences.

The INCAP group has shown that the integrated heart-rate method is capable of giving useful estimates of the energy expenditure of young children. These measurements will be continued in the next phase of the study. The Thai workers propose to carry out time-and-motion studies on their subjects. It was agreed that a high priority should be given to these estimates of energy expenditure. Such measurements will help to answer the third question posed in the 1977 report (1): "What are the factors associated with adjustments to low energy intakes?"

4.2.3. Digestibility of Protein

More attention needs to be given to the digestibility of protein in habitual diets. It is not clear why the digestibility of both Guatemalan and Thai diets is so low, or whether the faecal N is derived directly from the food or is mainly endogenous. The capacity of the Jamaica group for work with 15N might make possible an attack on this problem.

4.2.4. Nitrogen Balance

One outcome of the present studies may be that in the future there will be less emphasis on short-term N-balance measurements. As mentioned earlier, there is a fairly wide range of variation in N retention between and within individual children on the same diet. It seems likely that this variation is caused mainly by differences in urinary rather than faecal N output. It was therefore suggested that it might be useful, in future long-term studies, to make frequent measurements of 24-hour urinary N, to get a better estimate of day-to day variation.

4.2.5. Community Studies

The meeting ended with some discussion of the possibility of studies in the community, addressed particularly to the fourth question put forward at the 1977 consultation: "Are habitual protein and energy intakes adequate at usual infection loads?" A high priority should be given to devising ways and means of tackling this question. The present studies have already laid the groundwork. One cannot ask more of N-balance studies in a metabolic ward than to give a reasonable indication of where the "safe level" lies. This then has to be tested in larger numbers of subjects in the field.

References

1. FAO/WHO, Report of the First Joint FAO/WHO Expert Consultation on Energy Intake and Protein Requirements (FAO, 12-74 October 1977) (FAO, Rome, 1978).

2. FAO/USDHEW, Food Composition Table for Use in East Asia (DHEW Publication no. (NIH) 75-465) (US Government Printing Office, Washington, D.C., 1972).

3. FAD/WHO. Energy and Protein Requirements, Report of a Joint FAO/WHO Ad Hoc Expert Committee (Rome, 22 March-2 A,orit 1971),, (FAO Nutrition Meetings Report Series no. 52, Rome, 1973), (WHO Technical Report Series No. 522, Geneva 1973).

4. M.H.N. Golden, J.C. Waterlow, and D. Picou, Am. J. Clin. Nutr, 30: 1345 (19771.

5. J.D. Waterlow, P.J. Garlick, and D.J. Millward, Protein Turnover in Mammalian Tissues and in the Whole Body (EIsevier, Amsterdam, 1978).

6. R.A. McCance, E.M. Widdowson, T. Moran, W.J.S. Pringle, and T.F.. Macrae, Biochem. J., 39: 213 (1945).

7. H. Fisher, M.K. Brush, P. Griminger. and E.R. Sootman. Am. J. Clin. Nutr, 20 927 (1967).

8. H.H. Mitchell, Arch Biochem. Biophys., 21: 335 (1949). 9. W.M. Wallace, Federation Proceedings. 18: 1125 (1959).

10. UNU/WHP. "Protein Energy Requirements under Conditions Prevailing in Developing Countries: Current Knowledge and Research Needs," Fd. Nutr Bull., Supplement 1 (July 1979) (WHTR-1/UNUP-18)

11. D.W. Spady, P.R. Payne, D. Picou, and J.C. Waterlow, Am. J. Clin. Nutr., 29: 1073 (1976).

Participants

Dr. E.M. Demaeyer, Medical Officer, Nutrition, WHO, Geneva, Switzerland.

Dr. A. Jackson, Acting Director, Tropical Metabolism Research Unit, University of the West Indies, Kingston, Jamaica.

Dr. Kraisid Tontisirin, Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University. Bangkok, Thailand.

Dr. J. Périssé, Senior Officer, Food and Nutrition Assessment Service, Food Policy and Nutrition Division, FAO, Rome, Italy.

Dr. N. Rao Maturu, Nutrition Officer, Food Standards and Food Science Service, Food Policy and Nutrition Division, FAO, Rome, Italy.

Dr. B. Torún, Chief, Programme of Physiology and Clinical Nutrition, Institute of Nutrition for Central America and Panama, Guatemala City, Guatemala.

Dr. J. Waterlow (Consultant and Chairman), Professor of Human Nutrition, London School of Hygiene and Tropical Medicine, Keppel Street (Gower Street), London, WC1E 7HT, United Kingdom.

Dr. R. Weissell, Nutrition Officer, Food and Nutrition Assessment Service, Food Policy and Nutrition Division, FAO, Rome, Italy.

Observers

Dr. H.J.L. Burgess, Secretary, ACC Sub-Committee on Nutrition Secretariat, FAO, Rome, Italy.

Dr. W.L. de Haas, Assistant Secretary, ACC Sub-Committee on Nutrition Secretariat, FAO, Rome, Italy.

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