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Nutrition and chronic energy deficiency
Investigating the biological and social consequences of chronic nutritional energy deficiency
Investigating the biological and social
consequences of chronic nutritional energy
deficiency
J.V.G.A. Durnin
BACKGROUND
This report is based on a workshop convened by the United Nations University on behalf of the ACC Subcommittee on Nutrition in Washington, D.C., 30 October-1 November 1985. The workshop noted the lack of available information on the biological and social consequences of chronic nutritional energy deficiency, and considered ways in which more reliable information might be obtained. It discussed in detail and recommended three experimental protocols with the potential to generate more specific data on the effects of this serious condition.
Prevalence
While actual starvation is a relatively rare occurrence with the exception of certain parts of Africa, chronic energy deficiency is now the most important nutritional deficiency in the world. It often is only moderate in degree, but it represents a state of real deprivation. It exists in most developing countries and may well affect, in varying degrees, a considerable proportion of their populations.
Complicating Factors
Energy deficiency is almost inevitably accompanied by other kinds of disadvantages, such as poverty, poor hygiene, and poor health care. Thus, it is a complex situation, and it is difficult to disentangle the numerous factors on the basis of their relevant importance.
Although poor economic circumstances and chronic energy deficiency usually coexist in some fashion, the economists' idea of poverty does not always take into account the adequacy of energy intake. In many areas of the world, subsistence farmers, living perhaps in rudimentary huts with little or no monetary income, may have a diet that provides adequate energy for their physiological needs. The diet may have little variety and be very simple, but it may have sufficient energy.
Chronic energy deficiency may affect a community in ways that are well concealed superficially. Adaptations to conserve energy may have been made over extended periods of time that influence work output, active leisure activities, or body composition or growth. The adaptations may be extremely effective, but the cost in social and cultural terms, and perhaps in reduced resistance to disease, may not be acceptable.
Circumstances in which chronic energy deficiency may be present are, therefore, ones in which the condition may not be apparent, and its presence and its degree can be assessed only by appropriate measurements. Because such assessment requires very careful design, fairly large population groups, reasonably strict control of several variables, a range of nutritional and social measurements, a duration of months to years, and a number of trained investigators, it is not unexpected that these difficulties, coupled with expense, have resulted in almost complete absence of appropriate studies on the effects of chronic energy deficiency.
Adaptation to Low Energy Intake
Chronic energy deficiency, as its name implies, is intake of energy over a prolonged period that is less than desirable. This is not necessarily the same as low energy intake. To distinguish clearly between these conditions is not a minor linguistic quibble but is the source of one of the major problems in investigating this nutritional state.
A deficiency of energy can occur in persons who have to work moderately strenuously and who therefore have a relatively high energy output, but who may not have enough energy in their diet to cover leisure activities that are other than sedentary. Equally, energy deficiency may be present in those whose energy intake is so low as to prevent any strenuous physical activity, either at work or in leisure. In this case, it is likely that the condition would be widely disseminated throughout the population, and could be obviously detected by simple measurements of food intake.
In situations that would be unusual in the developing countries but can now be found in industrialized countries, it is quite possible for individuals, or even relatively large sections of certain populations, to have low energy intake and yet not suffer from chronic energy deficiency. Such individuals simply have a very sedentary existence, with no active leisure pursuits, and therefore have low energy requirements to maintain their chosen state. One distinguishing feature of such groups is that moderate obesity may be seen in some of the individuals.
Low energy intake can result in physiological adaptations. One of these is a fall in basal metabolic rate (BMR). This can be a protective reaction of major importance in reducing energy requirements.
In chronic energy deficiency with low intake, there also is a decrease in body mass and a reduction in the fat mass of the body, frequently to minimal or near minimal levels. Characteristics of populations that have endured this condition for generators are small adult stature and low body weight, the presence of very little subcutaneous fat, and retarded growth of children.
A behavioural form of adaptation is to reduce voluntary or discretionary physical activity; for example, less playing and exploring by children and less voluntary movement in adults. This may be very difficult to monitor, as it may coincide with the necessity of undertaking moderately strenuous physical activity at work. This reduced level of physical activity, however, which may be present at all ages, is probably the major factor in diminishing energy requirements, and is something that requires very careful consideration and measurement in any experimental study of this condition.
Questions Requiring Answers
There are two aspects to acquiring more definitive information on this problem. One is the question of what exactly the biological and social consequences of chronic deficiency of nutritional energy in a population are. That is, when energy intakes are less than the estimated desirable requirements, taking into account the need for sufficient energy to allow participation in many activities of social benefit to the community and to the family, as well as for the individual's own welfare, what are the disadvantages and what are the undesirable consequences of the adaptations that have taken place?
The second question is what the effects on work output and on the general way of life are if extra food energy is supplied to such populations.
The widespread existence of chronic energy deficiency throughout the developing countries of the world makes it very important to attempt to answer these questions. They are, however, extremely difficult questions to tackle in a way that will produce valid scientific data. It must be stressed that collecting anything less than well-substantiated data is likely to mislead us in interpreting the information, and may well result in conclusions being drawn that confer little benefit on these disadvantaged populations.
Methodological Difficulties
The examination of these problems involves considerable methodological difficulties at many different levels. First, determining whether or not significant chronic energy deficiency exists may pose a formidable task if we are considering a situation that is not especially severe. When energy deficiency exists but not in a flagrant form, which is almost certainly the most common, the types of measurements needed to define the precise degree of energy deprivation are laborious and complex. They are open to large variability, are difficult to interpret, may require large population groups from which to select a representative sample, and may necessitate sufficiently intensive investigation of the sample potentially to jeopardize the validity of the data. They properly require assessment of food intake, muscular development, fatness, and levels of physical activity (perhaps of energy expenditure), as well as various psychological and social variables.
COMPONENTS OF ENERGY USE
The quantity of energy required by the body varies depending
on the relative importance of several factors, principally: -the
size of the individual;
-body composition, particularly the proportion of lean tissue in
the body mass, which affects energy requirements both in basal or
resting conditions and in physical activity;
-the amount and intensity of physical activity, most obviously in
the occupation of the individual and also in leisure pursuits.
Age may exert an influence but is significant mainly indirectly through its effect on body size and on the amount of physical activity. Children, for example, have a relatively higher requirement of energy partly because they are growing, but growth by itself does not take very much extra energy, and the higher metabolism of children results mostly from their being more physically active. Similarly, older persons have lower energy metabolism, but again this depends not so much on any direct influence of age as on indirect ones of change in body composition - usually decreased muscle mass and increased fat mass-and a diminution of physical activity.
The sex of the individual, independent of the above influences, has little effect on energy requirements.
Energy Intake
The actual amount of energy available from the diet almost always has to be measured. This can be done in many different ways, depending on the desired level of accuracy, the size of the population sample, and the available technical assistance. The methods need not be described here, but they vary from detailed weighing and recording of all of the separate foods and drinks consumed by an individual during several consecutive days to an interview designed to determine the usual diet.
Anthropometry
Because of the considerable influence of both body size and leanness on energy metabolism, it is essential to have basic anthropometric information. Measurements include height, weight, skinfold thickness to estimate fatness, and some limb circumferences to indicate relative muscularity. These simple variables signify whether or not the growth of children, the height and weight of adults, and fatness and muscularity are normal for the type of community.
Basal Metabolic Rate
The BMR has considerable importance in relation to energy needs and energy deficiency. In most circumstances, for individuals with occupations involving a great deal of physical activity, the BMR accounts for about 60 to 70 per cent of the total daily energy expenditure. It also indicates chronic energy deficiency, as one of the adaptations to inadequate intake of energy is a fall in the BMR. In a community where low energy intakes are found, values of BMR that are lower than expected (relative to body size and composition) arouse suspicions of energy deficiency.
Energy deficiency that is not also accompanied by in take that is low in absolute values is unlikely to result in a low BMR.
Although the literature is imprecise on this issue, it appears that BMR does not become lowered unless there is an energy imbalance of probably several hundred kilocalories per day, and obviously this state would be unlikely to exist in an environment in which some sort of stable adaptability had been attained.
Of course, the stress of energy deficiency may have existed for a sufficiently long time, or may have recurred with enough frequency, for the BMR of the group to be significantly lower than average for a normal population.
A low BMR, therefore, usually indicates energy deficiency, but not all types of energy deficiency are necessarily accompanied by low BMRs.
Physical Activity
A quantitative assessment of the duration and type of physical activity and of its social and cultural implications may be of considerable consequence in determining the existence of chronic energy deficiency.
Physical activity is not only a major component of total daily energy expenditure; it is the major avenue for adaptation to inadequate energy availability.
There are various techniques for measuring physical activity, the details of which are not given here, but none of them is entirely satisfactory. They include observation of an individual's physical activity, both at work and in leisure; self-recording of activities (either of these sometimes is combined with measurements of energy expenditure); and the use of independent means to measure movement, such as heart-rate recorders and pedometers. There are also new (and very expensive) techniques for measuring total energy expenditure over 14 to 21 days, but these are not relevant to the present purpose.
Apart from the difficulty of actually measuring physical activity, there is the considerable problem of deciding whether the measured levels reflect curtailment due to inadequate energy availability. This can be determined only by either carefully collecting socio-cultural information or by discovering an increase in physical activity resulting from the provision of extra food energy.
Physical Capability
Because chronic energy deficiency often coexists with poor muscular development and low capacity for physical work, it may be useful to test the general ability to undertake physical effort. A low level of exercise capacity is indicated by failure to attain appropriate levels of physical exertion and by undue stress to the body during moderately strenuous activity. These can be assessed, even in difficult field circumstances, by simple exercise testing on a stationary bicycle or treadmill, or by the Harvard step-test.
Social and Cultural Adaptations
It is essential to obtain social and cultural information that may be relevant. Energy deficiency may be compensated for in ways that are reflected in work patterns, community actions, social activities, and other behavioural changes.
Morbidity
States of chronic energy deficiency are frequently accompanied by high rates of morbidity in a population. Assessment of this may indicate the possible existence of inadequate energy and also provide a baseline for comparison if remedial measures are introduced. To be reliable, morbidity information requires careful standardization, good rapport with and the co-operation of the population under study, and experienced medical supervision and interpretations.
EXPERIMENTAL DESIGNS
At least two potential approaches might be taken in the experimental investigation of chronic energy deficiency in the field. One involves intervention, whereby extra food is provided for some finite period and several variables are measured to determine whether or not significant improvements have taken place. Such interventionts) might be of relatively short duration or be made over more prolonged periods of time.
An intervention in which food supplementation is provided involves many serious difficulties and requires careful controls. For example, supplements are often given to specific members of a family group, such as pregnant or lactating mothers, and children, but it can frequently be an exacting task to monitor how much, if any, of the supplement has gone to the intended individuals and whether or not it has been a true supplement or only a substitute. Many possible confusing psychological influences that are not direct effects of the extra food itself may affect the measurements that are being made. These would show up mostly in relation to some social variables but could also affect work output.
A second approach is to make use of naturally fluctuating food availability or energy demands due to seasonal influences. These arise in certain areas of the world either intermittently because of poor harvests, or regularly when food may be relatively plentiful after harvest but be in short supply before harvest, or where labour-intensive activities increase markedly with no extra food coming into the household. If this state occurs consistently every year, an investigation could be mounted to study the seasonal alternations in certain values such as food intake, body weight and fatness, and levels of physical activity. The whole circumstance would obviously not be exactly comparable to one of long-standing constant energy deficiency, however, and it is difficult to distinguish whether activity alters as a result of changing work demand or whether the latter is responsible for changes in appetite and food intake.
Short-Term Intervention
The most practical and least costly intervention would be limited to two to three months plus four to six weeks of baseline studies before the caloric supplementation is initiated and for at least one month after it has been implemented. As in the case of longer intervention studies, it would be essential that the population selected should have a caloric intake sufficiently low to restrict physical activity. It would require evaluation of 24-hour physical activity and anthropometric measurements to assess body size and composition. Such a study would indicate changes in activity, but lasting social and economic effects could only be inferred.
Longer-Term Intervention
To determine long-term social and economic consequences of improving the dietary energy intake of chronically undernourished populations, the workshop recommended an intervention study of at least one year's duration preceded by extensive baseline studies. The observations would be the same in principle as for the short-term intervention study, but more sophisticated measurements of body composition would be useful as well as observations on all family members. Changes in social behaviour, economic status, and community activities should be looked for.
Seasonal Influences
A different type of energy deficiency can be studied in a community that has large fluctuations in either food availability or work levels, or both, due to seasonal influences. These populations would be agricultural, frequently living in areas of the world with two harvest seasons. The two harvests, even when not affected by drought or rains, often vary, and the availability of food could differ markedly at different seasons of the year unless the storage and use of food are organized very efficiently.
In this type of environment, the energy expended at work can also be variable; planting and harvesting require longer and heavier levels of work than other seasonal activities. Sometimes there is a combination of a higher requirement for work and lower availability of food.
Although these nutritional stresses do not necessarily affect all groups in the community equally-sometimes men, sometimes women are more at risk - they provide an opportunity for a non-intervention study.
Seasonal variations reflect only one form of energy deficiency, however, and could pose serious problems for an investigation because, among other difficulties, they could be considerably different from one year to the next. Moreover, it might be impossible to determine the existence of large seasonal fluctuations until a study was well under way, and it would seriously impair the study if no fluctuation did in fact occur. It is quite possible that an investigation might have to be curtailed or its venue changed because of an unusually good harvest. It would also be difficult to compare altered levels of energy deficiency to long-standing energy deprivation that might have existed for generations. Greater care might also be needed in taking measurements because of the relatively rapid nature of the fluctuations.
In spite of these drawbacks, seasonal influences on work output and food availability are important examples of types of energy deficiency. Examining them would be useful and might contribute significantly to the understanding of some forms of adaptation by the individual, the family, and the community.
PRACTICAL CONSIDERATIONS AND PRIORITIES IN RELATION TO THE TYPE OF STUDY
Intervention versus Non-intervention Studies
Intervention studies require both a control and an experimental population to discriminate between changes related and unrelated to the intervention. Ideally, there ought to be a similar type of intervention in the control group, with the exception of the nutritional supplement, because the presence of the investigators and all of the measurements being made might, by themselves, cause some changes in the variables. To carry this to extremes would be laborious, costly, and probably self-defeating, but it ought to be possible to make some appropriate, minor, non-nutritional intervention. In any case, intervention without a food supplement would be unlikely to affect biological values such as body weight and composition, although there is no guarantee that these would necessarily always increase as a result of supplements; a true increase in energy intake in an energy-deficient population could result in greater physical activity with no change in bodily dimensions.
A control group is certainly necessary. Matching the control and experimental groups exactly, without the one being aware of the existence of the other, might be difficult but not impossible. The two groups would have to have approximately the same apparent degree of energy deprivation, although this would be definitely determined only after collecting baseline data. One of the groups would then be subjected to the intervention of a food supplement, and both groups would be followed over a period of time to estimate the extent of biological, social, and cultural alterations.
In the case of the non-intervention or seasonal study, a control group would not be necessary, as the individuals being assessed would act as their own controls.
Shorter versus Longer Studies
The biological and social changes that might come about from the supply of extra food to a community could occur over very different time spans. It might be expected that some biological responses would appear relatively quickly-for example, weight and fatness (but not necessarily height or muscularity). This rapidity of response would be particularly likely to occur in certain types of individuals, such as children and lactating or pregnant women, or persons with moderately severe dietary deficiencies prior to the intervention. On the other hand, some social changes might take a long time to become measurable, even when levels of physical activity increase relatively rapidly.
Different types of responses would therefore be detected in short-term and in longer-term studies. While short-term investigations have several advantages- they produce some results quickly; they are less costly and thus can be undertaken in several localities simultaneously; and, because they are simpler, they may be less likely to encounter opposition - the information they provide is limited. For example, an increased level of physical activity in the short term may not necessarily continue. If it does, it may have a continuous effect that might exert considerable influence on the work output or the social activities of the community. Short-term studies, therefore, may require drawing inferences from limited data, and this disadvantage has to be considered carefully when making the choice of design.
In the end, the decision on the type of study to be done depends on the exact information required, the population to be examined, and, probably most important for the immediate future, the financial and technical resources available. Many arguments could be made in favour of relatively small, short-term studies that could be regarded as pilot projects and that, if successful in confirming behavioural changes, would encourage the mounting of larger, more ambitious, longer-term investigations.
Understanding the problems of chronic energy deficiency is of wide-spread and critical importance to very large populations throughout the world. Short term studies will not solve the problems or help us understand them fully. Because of the relatively untried nature of such an investigation, however, almost certainly the first priority is to mount perhaps two such projects, in carefully chosen environments, in the expection that reasonably rapid and successful collection of data will provide the evidence to generate support for several longer-term projects. The data should also be of direct assistance in planning longer term studies.