Expert consultation meetings that are convened to make recommendations on nutrient requirements are sometimes faced with situations in which adequate information is lacking and questions need to be answered before evidence-based recommendations that are applicable to population groups worldwide can be provided. Recognition of the lacunae in the existing knowledge base helps the identification of potential areas for future research and investigation by the wider scientific and academic communities. The deliberations and recommendations of experts in this important sphere carry much weight within the academic community, as well as with research funding bodies, international agencies and bilateral donors.
The following recommendations for future research are based on the topics and issues that were identified during the more focused discussions at the preliminary working group sessions, and that were fed into the expert consultation, as well as on those identified by the experts themselves during the consultation. However, as the present expert consultation acknowledged, it is not enough to come up with a wish list of research topics without prioritizing what needs to be done. With resources becoming increasingly limited, the experts recognized that it would be futile either to outline research needs too broadly or to attempt to include every conceivable topic that may be relevant to the issues raised during their deliberations. The expert consultation recognized the need to make judgements on priorities when they stated: "We need to prioritize our recommendations so as not to dilute the strength of our requests."
The questions and topics that the 2001 expert consultation identified as being in need of further investigation are categorized into two broad groups. The first group consists of those biological questions whose answers will provide better numerical estimates of human requirements. These include conceptual, methodological and data-gathering components. The second group includes epidemiological and community studies aimed at testing the validity of the estimates in populations living in different environmental and social conditions, for which more general, and indeed more realistic, criteria of health and function are required than those that are used in metabolic or clinical investigations. This second group also includes questions that relate to the use of the recommended nutrient requirement estimates and their implications for planners and policy-makers at the national, regional and global levels.
8.1.1 Basal metabolic rate (BMR) and total energy expenditure (TEE)
1. BMR predictive equations are to be revisited, reviewed and reformulated, if necessary, based on access to a larger, more comprehensive global database that should be expanded and collated with strict and transparent quality and inclusion criteria.
2. There are insufficient data to judge whether either ethnicity or habitation in a tropical environment influences BMR. It is possible that aspects that are attributed to ethnicity may well be responses to early life exposure to suboptimal nutritional environments. It is therefore recommended that when ethnicity is researched and reported, additional information on history of nutritional status and/or environmental exposure in early life also be measured and reported. This phenomenon needs to be better understood, the physiological basis needs to be established and the plausible mechanisms involved need to be clarified.
3. Prospective studies to measure daily TEE by DLW and/or other methods (such as the flex-heart rate method) need to be undertaken in order to provide comparisons for the same subjects with estimates based on the factorial method. Measured BMR and the energy cost of sitting, standing, etc. may be used with the PAL values presented here for calculating daily energy expenditure in an effort to enhance the application of these PAL values. There is accumulating evidence from various laboratories of discrepancies between estimates of TEE by the factorial method using published PAL values compared with estimates using other methods, such as the flex-heart rate method. This discrepancy becomes more apparent when the intensity of an activity is increased. Studies comparing the two methods using different sources of PAL values suggest that it may be possible to use these data more appropriately and to reconcile the data generated. Given the shortage and inordinate expense of stable isotopes, it is necessary to invest more in accepted methodologies in order to broaden the database. There is also a need for more data on PAL values.
4. There is an urgent need for more TEE and measured BMR studies, coupled with time-motion studies from developing countries that cover prevailing and changing life styles. The use of DLW studies will be essential for the purpose of validating existing methodologies and developing new ones. Support from the International Atomic Energy Agency (IAEA) in making available more isotopes at less cost, in improving the ability to analyse these and in general capacity building to cater to developing country needs is crucial in this area.
5. There is shortage of information on BMR and TEE from elderly groups because this subpopulation is increasing owing to changes in longevity and demographics in developing and developed societies.
6. Further development and validation of techniques for measuring TEE and BMR, as well as energy cost of activity expenditures and patterns, need to be supported. New techniques should be accurate, precise, portable, cheap and appropriate for field-based studies worldwide. Ideally, all new techniques need to be validated against both indirect calorimetry and DLW methods.
7. There is a need to update and expand the data bank on the energy cost of a range of activities undertaken in real-life conditions by children and adults, distinguishing weight-bearing from non-weight-bearing activities, and specifying whether energy cost refers to "net" activity or is integrated over tasks.
8. The number of available DLW studies on infants (and young children) from developing countries is limited and needs to be expanded in normal birth weight infants.
9. Studies with DLW (or other methods) need to be carried out in order to determine TEE of school-going children and adolescents in urban and rural areas of developing countries.
10. The DLW method provides a means of determining the amount of energy expended in physical activity. PALs consistent with normal health and the development of infants and children should be described qualitatively and ethnographically across cultures.
11. Further studies are needed to confirm whether the increased TEE observed in some settings is caused solely by differences in size and body composition or whether other mitigating factors are involved.
12. More information is needed about the influence of habitual physical activity on the growth and development of all children and adolescents, and on the duration, intensity and frequency of the physical activity that is necessary to achieve optimal effects.
8.1.2 Nutritional anthropometry and body composition
1. The use of United States-based reference data for assessing adolescent growth worldwide is a matter of concern, and it is recommended that research be conducted in order to evaluate their universal applicability, specifically the upper percentile elevations and skewness of the NCHS value, especially as they apply to developing countries.
2. More data are needed on variations in body composition of individuals in different population groups. There is a further need to develop methodologies for body size normalization when estimating the energy cost of different activities.
8.1.3 Studies in undernourished subpopulations
1. The effect of the quality of dietary protein, carbohydrate and fat on rates of weight gain, particularly during the recovery period from malnutrition, needs to be understood better. Biological (and behavioural) studies are needed to help establish appropriate levels of energy intake during convalescence from such episodes.
2. Nutrient needs for the rehabilitation of stunted children are also poorly understood. Information is needed on the energy intake and expenditure requirements for catch-up growth in body mass and stature of stunted and undernourished children. Special nutrient requirements for catch-up growth of bones require further research. Physiological adjustments in physical activity and growth in response to undernutrition should be investigated with newer methodologies such as DLW.
3. There is a need for estimates of BMR and TEE using DLW methodology in undernourished children and adults. This should include an investigation of intra-uterine growth retarded (IUGR) infants, and stunted and undernourished groups of children, compared with children with adequate growth.
8.1.4 Food energy
1. Factors affecting the dietary intake that is necessary to satisfy energy requirements should be explored, including diet digestibility, viscosity, and energy and nutrient density.
2. The validity of metabolizable energy (ME) food energy conversion factors as quantitative equivalents of biologically useful, energy and their relationship to net metabolizable energy (NME) need to be reviewed. It may be necessary to investigate how best NME and energy requirement estimations can be integrated and reconciled.
3. The AOAC (Prosky) method of dietary fibre analysis is now widely used in food analysis. Further research is needed to develop reliable analytical methods for resistant starches.
1. Large numbers of children in developing countries have experienced repeated episodes of infections, which are often accompanied by a negative energy balance owing to decreased appetite and/or increased metabolic activity. Studies on the effects of infection on energy requirements of infants are limited, and should be expanded to cover a broad range of infectious agents of varying severity and duration.
2. More qualitative and quantitative information is needed on the habitual physical activity of children and adolescents in developing societies. This includes physiological, anthropological and behavioural studies. Anthropologists and other social scientists must be invited to participate in this endeavour, as information already exists in reports and monographs in the social sciences literature, and this should be analysed.
3. Currently, there are major gaps in the knowledge regarding estimating the survival level of energy expenditure, and consequently the lower limits of emergency rations and food aid baskets, particularly in refugee settings. This is in need of urgent evaluation. The support of FAO/WHO is essential if the academic community is to obtain funds for such investigations from research organizations.
4. There is a general consensus that the most crucial aspects in understanding the energy requirements in pregnancy and lactation are now known. However, more research with respect to public health-related issues (e.g. low birth weight) should be carried out. There is a need for longitudinal studies on pregnant woman, in order to relate the associated physiological parameters with birth outcomes and risks. More research is needed on the range of issues that affect obese and underweight women during pregnancy and lactation.
5. There is a need to establish the nature, duration, frequency and intensity of physical exercise required to maintain generally good health and to prevent specific pathologies, such as obesity and its related co-morbidities.
6. There is a need to understand better the health risks of people with BMI less than 18.5.
7. Overweight and obesity are closely linked to a positive (i.e. surplus) energy balance. Biological and behavioural investigations are needed to develop and test methods that will guide children and adolescents towards an energy balance that reduces the risk of becoming overweight.
8. Techniques must be developed to stimulate childrens and adolescents interest in performing an appropriate level of physical activity in the context of different geographic, cultural and socio-economic environments.
9. Reliable documentation on life-styles and time use needs to be collected in order to improve the existing energy expenditure estimates using adults, children and the elderly in diverse contexts, with special efforts to include information from developing country and transitional society contexts.