The primary aim of the expert consultations on nutrient requirements has remained the same: to provide advice on scientific issues related to nutrient requirements and to formulate appropriate recommendations for action. An examination of the historical precedents in this endeavour reveals how the various expert groups have contributed to the principles for determining human energy requirements and their practical applications, which have been adopted worldwide. The recommendations from the resulting reports have not only reflected the state of knowledge at particular points in time, but have also been embraced by the global scientific community, thereby influencing research agendas and methodologies over the years.
Many of the points made by the first committee on calorie requirements, which met in 1949, are still pertinent today. The requirements set by the experts were intended for groups of people rather than individuals, and the committee established the principle, which is often misunderstood, that "an average requirement can never be compared directly with an individual (requirement)" (FAO, 1950). The first committee noted that its recommendations should be adjusted depending on how and for whom they are used, and it cautioned that nutrition and health experts within countries should take into account local conditions in applying the requirements. There is always the need to exercise judgement in interpreting and using requirement values, yet advice in this area is most difficult to impart to users. The first committee on calories offered the very practical rule of thumb that if the person "is in good health and calorie balance, that is, neither over- nor underweight, then he or she is consuming food according to his or her calorie requirements" (FAO, 1950). Subsequent committees also recognized the importance of maintaining an adequate level of energy expenditure, thus acknowledging that non-occupational activities were just as important as occupational ones to the overall health status of many people and that energy requirements did not refer to a minimum level (FAO, 1973).
The 1973 Report of the Joint FAO/WHO Ad Hoc Expert Committee on Energy and Protein Requirements reiterated statements that had been made in past reports that the recommendations for nutrient requirements should be applied to groups and not to individuals. However, the 1973 report also made two additional important points: 1) that estimates of requirements are derived from individuals rather than groups; and 2) that the nutrient requirements of comparable individuals often vary.
The report of the Joint FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements held in 1981 (WHO, 1985) was very clear in its statement that estimates of energy requirements should, as far as possible, be based on estimates of energy expenditure, as the prevailing method of determination - from observed intakes of food energy - was becoming unreliable and served to support a circular argument that access to food determined energy needs. The rationale for this conclusion was that in both developing and developed countries actual energy intakes are not necessarily those that either maintain a desirable body weight or provide for optimal levels of physical activity, and hence health in its broadest sense. The experts at the 1981 consultation were aware of the limited data on energy expenditures, particularly among children. They were also conscious of the fact that no reliable and widely useable method was available to the scientific and academic community for collecting such data from a range of population groups worldwide.
The 1981 expert consultation felt that, except for children, sufficient information was available to approach this issue using data on BMR at the centre of a new conceptual framework to estimate total energy expenditure. Thus the use of BMR became important in determining energy requirements. The experts identified a new methodology for calculating energy requirements, and substantial research that needed to be carried out after the expert consultation. One significant departure of the 1981 expert group from that of the 1971 experts was the rejection of the concept of a single reference man or woman. The 1971 group defined such people as "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" (FAO/WHO, 1973). The 1981 group found this concept too restrictive and not reflective of the wide ranges of both body size and patterns of physical activity.
In keeping with each of its predecessors, the present report has attempted to build on these efforts, while also moving forward in breaking new ground. The 2001 Joint FAO/WHO/UNU Expert Consultation on Human Energy Requirements met after a lapse of nearly 20 years and deliberated only the requirements of energy in the diet, leaving deliberations and debates on protein and amino acid requirements to a separate expert group, which met at WHO in Geneva in 2002. Following up on the recommendations arising from the Energy Consultation, FAO also convened a group of experts to discuss the issue of "food energy", because recommendations for optimal energy requirements become practical only when they are related to foods that provide the energy to meet those requirements. Gains in understanding of the digestion and metabolism of food and the increasing sophistication of analytical techniques meant that the various options available to express the energy value of foods needed to be standardized and harmonized. The recommendations of this group have since been published (FAO, 2002) to complement this report.
When the Expert Consultation on Human Energy Requirements met in 2001, the situation regarding lack of data to arrive at realistic and evidence-based recommendations had changed dramatically. Major technological advances using stable (i.e. non-radioactive) isotopes had by then had a dramatic impact on the measurement of energy expenditures of free-living individuals in real-life situations. Estimates based on these measurements have, to a large extent, replaced estimates using both direct and indirect calorimetry and the associated dependent methodologies such as heart rate monitoring, activity monitoring, pedometers and actometers. It is important to reiterate that these conventional methods continue to be important because the stable isotope technique measures cumulative total energy expenditure over a period but provides no accurate estimate of day-to-day variations, or information relating to the nature and pattern of daily activities. Thus, in this report, almost all of the recommendations made are based on reliable measurements of TEE obtained from infants, children, adolescents, adults and the elderly, as well as from women in special physiological states such as pregnancy and lactation.
A summary of the new concepts and changes in this 2004 expert report include the following:
The calculation of energy requirements for all ages should be based on measurements and estimates of total daily energy expenditure, including the energy needs for growth.
New values for energy requirements of infants, children and adolescents were proposed because existing values had been overestimated for children under ten years of age, and underestimated for children over 11 years of age and for adolescents.
Different requirement levels were proposed for populations with various lifestyles and levels of habitual physical activity, starting at six years of age.
A comparison and testing of the different BMR databases with varying degrees of ethnic and geographical coverage was carried out to determine whether new equations for estimating BMR from mean age and body weight of population groups were needed (Annex 3).
New factorial estimates of the additional energy needs imposed by pregnancy and lactation were applied.
Recommendations for the levels of physical activity required to maintain fitness and health and reduce the risk of developing obesity and diseases associated with sedentary lifestyles were made, and PALs based on the degree of habitual activity recommended for long-term good health were classified.
From the start, most expert groups have sought to address the practical application of the requirements. Time and events have shown that this aspect is as complex as determining the requirements themselves. As in the 1985 report, the section on issues regarding the application of requirements has been omitted from this report. However, in keeping with the recommendation made by the experts, the FAO Secretariat has spent time and effort in developing both a users manual and a software application (on CD-ROM, see Annex 4), which are released alongside this report so that they might complement each other. Both the scientific content and the recommendations that ensue from this evidence base, as well as the usefulness and appropriateness of the accompanying applications manual and software, will await the judgement of the community of users, who are the best arbiters of the importance of this ongoing exercise by international agencies.
FAO. 1950. Calorie requirements: report of the Committee on Calorie Requirements. FAO Nutritional Studies No. 5. Washington, DC.
FAO. 2002. Food energy - methods of analysis and conversion factors. FAO Food and Nutrition Paper No. 77. Rome.
FAO/WHO. 1973. Energy and protein requirements: Report of a joint FAO/WHO ad hoc expert committee. FAO Nutrition Meetings Report Series No. 52. WHO Technical Report Series No. 522. Rome and Geneva.
WHO. 1985. Energy and protein requirements: Report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series No. 724. Geneva.