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In 1948, three years after the founding of FAO, the newly established Standing Advisory Committee noted that “the problem of assessing the calorie[1] and nutrient requirements of human beings, with the greatest possible degree of accuracy, is of basic importance to FAO” (FAO, 1950). As a result, a gathering of experts was convened in September 1949 to address the issue of calorie needs. The foreword of the report of this meeting stated that “even tentative recommendations would be of immediate practical value to FAO but also to its member countries” and that the recommendations would also be of value to “nutrition workers and others concerned with the problems of food requirements” (FAO, 1950).

This Expert Committee meeting was the first of what was to become a recurrent activity within FAO, to begin with on its own, but later in collaboration with other United Nations organizations, most notably the World Health Organization (WHO). Since the 1949 meeting, energy requirements were reviewed again in 1956 (FAO, 1957a); protein was investigated in 1955 (FAO, 1957b) and 1963 (FAO, 1964), and energy and protein were reviewed together in 1971 (FAO, 1973) and 1981 (WHO, 1985). More recently, energy was reviewed in 2001 (FAO, 2004), and protein in 2002 (WHO, forthcoming).

Over the years, energy requirement recommendations have been used for many purposes by scientists, planners, policy-makers, regulators, etc. Among these uses are: 1) assessment of the energy needs of countries, populations and subgroups of populations living under different circumstances; 2) assessment of food availability within regions and countries; 3) assessment of the potential ability of available food supplies to meet a country’s or a population’s needs, during normal circumstances or acute shortages; 4) assessment of individuals’ diets (although the recommendations are not meant for this purpose, they are commonly used for it as there is no other broadly applicable international standard); and 5) as a basis for food labelling, with implications for consumer information/education about specific foods, regulatory compliance regarding nutrient content and claims, and trade. All these uses relate to one of the issues recognized by the first committee - that whereas the recommended requirement values were determined at the physiological level, a country’s food supply is estimated at the production or retail level, and therefore some adjustment is required when comparing the two levels (FAO, 1950).

Experience over the years has revealed that practical application of the requirement recommendations continues to be both elusive and complex. The 1949 group called on food economists to assist in the assessment of energy needs, but this collaboration has never been fully realized. Initially, the reviewing experts assigned to the Secretariat the mandate of preparing a chapter or section of the report to address the practical applications of the requirements, but this aspect was found to be increasingly problematic and requires more attention.


In 2001, FAO, WHO and the United Nations University (UNU) convened an Expert Consultation on Energy in Human Nutrition, which provided the most recent review of requirements and other energy-related topics (FAO, 2004). As part of the preparatory process for both the Joint FAO/WHO/UNU Expert Consultation on Energy and that on Protein and Amino Acids in Human Nutrition five working groups were created and convened in June 2001 to deal with various topics that required a more thorough review than the others. Working Group 5 was devoted to Analytical Issues in Food Energy and Composition: Energy in Food Labelling, including Regulatory and Trade Issues (see Annex II), and was created partially in anticipation of possible changes in the energy requirements that may have resulted from the new requirements being based totally on energy expenditure data.[2] In addition to discussing the preferred methods of protein, fat, carbohydrate and dietary fibre analysis, Working Group 5 also considered the following in its deliberations: 1) the routes of energy loss from the body such that the lost energy cannot contribute to maintaining energy balance; 2) the size of the energy loss for each of the energy-providing substrates, including fermentable carbohydrate; 3) variations in the energy losses reported in different studies of food components; 4) energy losses from normally consumed foods that have not previously been taken into account; and 5) factors external to food energy availability that modulate energy needs and the ability to maintain energy balance. Taking all of these into consideration, possible approaches to energy evaluation, including ways to account for diet-induced thermogenesis, were discussed. At about this time, the Codex Committee on Nutrition and Foods for Special Dietary Uses (CCNFSDU) requested FAO’s assistance in harmonizing energy conversion factors, and thus enabling uniformity in labelling and in the information provided to consumers (CCNFSDU, 2001a; 2002). This request was reinforced by the introduction of the information paper by the Australian delegation at the 23rd CCNGSDU session in 2001 (CCNFSDU, 2001b).

As alluded to in the previous paragraph, the expected adoption of new energy requirement values based on energy expenditure raised the issue of how best to match requirements with food intakes. This topic was briefly introduced and discussed at the 2001 Expert Consultation on Energy in Human Nutrition, but the experts present at that meeting were primarily physiologists and felt that the subject was outside their area of competence. Thus, a Technical Workshop on Food Energy: Methods of Analysis and Conversion Factors took place in Rome from 3 to 6 December 2002 to review the subject further (see Annex 1 for the list of participants at that workshop). To provide continuity between Working Group 5 and this technical workshop, the chairperson and one other member of Working Group 5 also participated in the technical workshop. The background papers and conclusions from Working Group 5 were considered extensively and were integrated, in some cases with modifications, into the present recommendations on methods of analysis and food energy factors. The goal of the technical workshop participants was to make recommendations on both methods of analysis and food energy conversion factors that would: 1) be analytically accurate; 2) if possible, tie conceptually to the physiological underpinning of the methods used to estimate energy requirements; 3) be acceptable worldwide, in terms of cost, complexity and compatibility with currently used approaches; 4) be acceptable to a broad variety of stakeholders - e.g. nutrition scientists, public health professionals, consumers, policy-makers, regulators and industry; and 5) based on these, foster harmonization.

The following sections of this report deal with several important and related issues. Chapter 2 describes the various methods of food analysis, reviews the current status of the analytical methods for proteins, fats and carbohydrates and makes preferred recommendations for use in food analysis based on the current state of the art and the available technology. Chapter 3 looks at the energy flow in the body and provides a theoretical framework for the use of appropriate energy conversion factors to estimate the energy content of foods. It describes the various energy conversion factors in current use and distinguishes the differences among them. It also highlights the need to standardize the energy conversion factors and reviews the implications of changes in current practices for the wide range of stakeholders in the food and nutrition sector. The final chapter (Chapter 4) summarizes the technical workshop’s views on how it may be possible to integrate methods and factors into a coherent approach to estimation of the energy contents of the macronutrient components of foods and diets.


Energy requirement recommendations remain “theoretical” and of little practical value until they can be related to foods, which provide the energy to meet requirements, and food intakes. Two pieces of information are needed in order to translate individual foods, and ultimately diets, into energy intakes that can be compared with the requirement recommendations. First, the composition of foods for those components that provide energy - i.e. the amounts of protein, fat, carbohydrate, etc. - must be analysed using appropriate methods. Second, these amounts of components must be converted into energy content using an agreed set of physiology-related factors that correspond to the energy-producing potential of the components in the human body. Thus, in order to make accurate estimates of energy intake, it is essential to have energy conversion factors for each component that denote the energy per gram for that component. However, it has long been recognized that the energy contents of protein, fat and carbohydrate differ, both inherently in the compounds themselves and owing to their different digestion, absorption and metabolism. Understanding of foods and nutrition has become increasingly sophisticated over recent decades, particularly regarding enhanced understanding of the relationship between diet and health. Much of the work of the first part of the twentieth century was directed towards understanding the roles of specific nutrients in intermediary metabolism: the goal of an adequate and healthy diet was to prevent energy and nutrient deficiencies. There is now increasing awareness of the key role that diet plays in the induction or prevention of specific diseases, such as heart disease, strokes, cancer and diabetes mellitus (WHO, 2003). Inadequate energy intake still limits the potential of individuals in many developing countries, while excess energy intakes are increasingly leading to very high prevalence of obesity (with its attendant complications) across all socio-economic strata in both developing and developed countries.

As understanding of foods and nutrition grows, the analytical methods used to determine food components become increasingly sophisticated. Newer methods allow more precise separation of the various macro- and micronutrients in foods. In the case of energy, each of the energy-providing constituents can now be broken down into a variety of subfractions or components. Carbohydrates, for example, can now be analysed to provide the amounts of specific mono-, di-, oligo- and polysaccharides, the latter comprising both starch and non-starch polysaccharides. Dietary fibre, which includes non-starch polysaccharides and has both a physiological and an analytical connotation, can be analysed directly. The ability to carry out these more complex and precise analyses has, in turn, facilitated a more sophisticated understanding of the nutritional, physiological and metabolic effects of these components and their relationship to health.

The interplay between analytical and physiological advances has made the field of nutrition increasingly rewarding, but also increasingly complex. In the case of the macronutrients that provide energy, there are now a number of different methods of analysis and different energy conversion factors. Each of the energy-providing components of foods is associated with its own variety of analytical methods, each of which may arrive at a slightly or very different value for the actual content of protein, fat, carbohydrate or dietary fibre. Each of the components also has its own energy value (or in some cases, values) - which in the case of “subfractions” may or may not differ from the value generally assigned to the macronutrient itself. This issue is complicated further by the fact that the energy conversion factor chosen is not necessarily tied to the specific analytical method used. The possibility of using any one of several analytical results with any one of several conversion factors results in myriad possibilities for expressing the energy content of individual foods, with consequent effects on estimation of the overall energy content of diets. Although this situation has become more complex over time, it is not new, and FAO has been recognizing and addressing it since as long ago as 1947.[3]

[1] During the early years of FAO, within the general scientific community energy was referred to in terms of “calories”, the unit then applied to expressing energy. In fact, the correct unit is “kilocalorie” (kcal), and increasingly the convention is to use kilojoules (kJ), with 1 kilocalorie equal to 4.184 kJ.
[2] In fact, the resulting recommendations for younger age groups were significantly different from those made in the 1985 report.
[3] In 1947, an Expert Committee on Calorie Conversion Factors and Food Composition Tables stated: “FAO should ... develop the principles on which average food composition figures ... should be based, ... whereby comparability of data for international use can be attained, ... at the earliest possible time ... including, if necessary, the revision of tables at present used.” (FAO, 1947).

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