Part IV: Summary of the draft fi ndings of the Joint FAO/WHO/UNU Expert Consultation on human energy requirements

Robert Weisell
FAO, ESNA
Rome, Italy

Introduction

One of FAO’s first tasks upon its founding and perhaps partly the impetus behind its founding was addressing the catastrophic food shortage in Europe in the aftermath of the Second World War. However, in assessing whether food supplies are adequate to meet a population’s nutritional needs, one must know the human energy and nutrient requirements. Determining energy requirements for assessing the nutritional situation has been one of FAO and WHO’s longest ongoing activities. In 1948, the newly established FAO Standing Advisory Committee considered that “the problem of assessing the calorie and nutrient requirements of human beings, with the greatest possible degree of accuracy, is of basic importance to FAO”.

First committee on energy requirements, September 1949

As a result, a gathering of experts was convened in September 1949 to address the issue of energy needs. In the foreword of the report of this meeting, the first Director of the Nutrition Division, Dr Wallace R. Aykroyd, observed that “even tentative recommendations would be of immediate practical value to FAO but also to its member countries”. The tentative nature of the recommendations remains true today. Once recommendations are made based on the data available, there should then be no reluctance to revise those recommendations based on new data.

The first committee on energy requirements made a number of points that were reaffirmed by subsequent groups and are still pertinent today. The requirements were intended for groups of persons rather than individuals, and the committee established the principle that “an average requirement can never be compared directly with an in- dividual (requirement)”. 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.” Early committees had the insight of adding the notion of maintaining an adequate level of energy expenditure, thus recognizing that leisure activity and health-promoting activity were important and that the requirements were not equated with a minimum, survival level.

The first committee noted that recommendations should be adjusted to accommodate individual needs and conditions, and cautioned that nutrition and health experts within countries should account for local conditions in applying the requirements. This need to exercise judgement in interpreting and using requirement values applies today, yet it can be a difficult concept for users to understand. Another issue addressed by the first committee was the fact that whereas the recommended requirement values were determined at the physiological level, the country’s food supply is often estimated at the retail level, and therefore some amount of adjustment is required.

Later committees refined, revised and introduced new concepts, but the basic concepts noted above remained. The subsequent committees also emphasized the important relationship between calories and other nutrients, stressing that sufficient energy should not necessarily be equated with adequate nutrition.

The most crucial difference between the determination of energy and the other macro- and micronutrient requirements is that energy requirements must be presented as an average, that is, half the homogeneous population will be below the mean and half above, while the other requirements such as for protein were presented at the top end of the normal distribution of intakes or needs, at a level termed “safe level of intake”.

One significant departure of the 1981 expert group from that of the 1971 expert group was the rejection of the concept of a reference man or woman. The 1971 group defined such persons as an “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”. The 1981 group found this concept too restrictive and not reflective of the wide range of both body size and patterns of physical activity. Previous expert groups had expressed a preference for basing energy requirements on actual expenditure data, since energy intake in many parts of the world is insufficient to maintain desirable body weights or optimal levels of physical activity. However, the data were lacking. By 1981, sufficient information existed to use energy expenditure as the determinant for energy requirements of all age groups except for children under ten years. This allowed the basal metabolic rate (BMR) to become the basis for expressing energy requirements. Because the experts proposed this new methodology for calculating energy requirements, there was a need for substantial research to be carried out after the Expert Consultation. This need for additional research was the major reason for the delay in the consultation’s report. During the four-year interval, a complete database of BMR measurements, mostly gleaned from the scientific literature, was established as well as information on activity patterns in various societies and energy expenditure levels for various tasks.

FAO expert meetings and reports on energy requirements

September 1949 - Calorie requirements: report of the Committee of Calorie Requirements. FAO Nutritional Studies, No. 5, 1950.

September 1956 - Calorie requirements: report of the Second Committee of Calorie Requirements. FAO Nutritional Studies, No. 15, 1957.

March-April 1971 - Energy and protein requirements: Report of a Joint FAO/WHO Ad Hoc Expert Committee. FAO Nutrition meetings Report Series, No. 52, 1973 and WHO Technical Report Series, No. 522, 1973.

October 1981 - Energy and Protein Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation. WHO Technical Report Series 724, Geneva, 1985.

October 2001 - Energy in Human Nutrition: Report of Joint FAO/WHO/UNU Expert Consultation. FAO (in press).

The joint FAO/WHO/UNU expert consultation on energy in human nutrition- FAO, Rome from 17 to 24 October 2001

From the perspective of the experts, the conclusions and recommendations from this consultation were based upon much more robust data and information than previous consultations. Although some of the conclusions have not changed, the experts felt that the conclusions were reconfirmed with stronger data.

The major concepts and changes coming from the 2001 Expert Consultation include:

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 since they had been overestimated for children under ten years of age and underestimated for children 10 years or older and adolescents (see Figure 1).

Beginning with six years of age, different requirement levels were proposed for populations with various lifestyles and levels of habitual physical activity.

Comparison and testing of the different BMR databases with varying degrees of ethnic and geographical coverage were carried out to determine whether new equations for estimating BMR from mean age and body weight of population groups were needed.

Apply new factorial estimates of the additional needs for energy imposed by pregnancy and lactation

Classify physical activity levels based on the degree of habitual activity recommended for long-term good health.

Provide recommendations for physical activity levels for the maintenance of fitness and health and for the reduction of the risk of developing obesity and diseases associated with sedentary lifestyles (see Table 1).

FIGURE 1. COMPARISON FOR GIRLS OF PROPOSED ENERGY REQUIREMENTS (-) WITH FAO/WHO/UNU (1985) REQUIREMENTS (- - -)

However, as mentioned previously, a number of principles articulated in earlier consultations remained true. The definition of energy requirement was modified slightly from that used in 1981 with the changes enhancing the clarity and preciseness of the definition.

“Energy requirement” is the amount of food energy needed to balance energy expenditure in order to maintain body size, body composition and a level of necessary and desirable physical activity consistent with long-term good health. This includes the energy needs for optimal growth and development of children, and the deposition of tissues during pregnancy and secretion of milk during lactation consistent with good health of mother and child.

FIGURE 2. DISTRIBUTION OF ENERGY REQUIREMENTS OF A POPULATION GROUP OR CLASS OF INDIVIDUALS

In addition, the consultation reconfirmed that the “recommended level of dietary energy intake” for a population group is the mean energy requirement of the healthy, well-nourished individuals who constitute that group. The experts noted that energy requirement estimates refer to groups, not individuals. However, groups do not have requirements, individuals do, and the estimates are determined from those individuals (see Figure 2).

The main objective for the assessment of energy requirements is the prescription of dietary energy intakes compatible with long-term good health. Therefore, the levels of energy intake recommended by this Consultation are based on estimates of the requirements of “healthy, well-nourished” individuals. It is recognized that certain populations have particular public health charac- teristics that are part of their usual “normal” life. Foremost among them are population groups in many developing countries that include numerous infants and children with mild-to-moderate degrees of malnutrition and who experience frequent episodes of acute diarrhoeal and respiratory infections. Special considerations are made in this Report for such populations.

From the very first consultation, it was agreed that energy requirements should be based on expenditure and not intake, but until 1981, data were lacking for applying the preferred methodology. Even in 1981, the data were lacking for children less than ten years of age. However, for the most recent expert consultation, sufficient data on energy expenditure were available for all age groups to allow the requirements to be based on energy expenditure.

In the most recent consultation and also in previous ones, the question of “requirement for what?” was raised. It was agreed that the normative approach should be used to avoid making recommendations that promote the undesirable status quo. Whereas the question of whether or not there was adaptation to lower energy requirements was a major issue in 1981, by the time of this consultation, the concept of costless adaptation was rejected. The experts agreed that there is never costless adaptation as there will always be a consequence to low-energy intakes in either physical (weight, height or body composition) terms or activity terms.

It was agreed that the doubly labelled water (DLW) method was the most accurate method for determining total energy expenditure (TEE). However, it was recognized that insufficient data existed for some age groups, and the volume of information from the developing world was sparse. For infants, it was agreed that sufficient data existed to rely on the DLW as the accepted methodology. When DLW is not feasible owing to economic or technical constraints, other methods such as heart rate monitoring and tri-axial accelerometers can be used to estimate the mean TEE of groups provided that they have been validated against DLW. This was determined to be the most feasible method for children.

The continued use of the factorial approach (BMR × physical activity level (PAL) = TEE) was recommended for determining the energy expenditure of adults, given the lack of a representative DLW dataset throughout the world. An example of this methodology is given in Table 2. There was a strong recommendation that more DLW data be collected in the developing world.

In recommending the continued use of the factorial method and its strong reliance on the BMR, the expert consultation recognized the past criticism of the equations used for calculating BMR based on body weights. It was agreed that a review of the expanded database of BMR values and the resulting derived equations should be carried out to see if a more valid equation could be adopted. This review is ongoing.