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* Working group members: WATERLOW (U.K., Chair), POLLITT (U.S.A., Co-Chair), ADAIR (U.S.A.) DURNIN (U.K.), JAMES (U.K.), PRENTICE (U.K.), VAN RAAIJ (Netherlands).
1. Introduction
2. Pregnancy
3. Lactation
4. Children
5. Conclusion
The working group took as
its main remit examination of the question: does new knowledge
require changes in the estimates of energy requirements of
pregnant and lactating women and children in the 1985 FAO/WHO/UNU
report? These groups have traditionally been considered to be
most at risk of having inadequate energy intakes.
There is new evidence to suggest that, except for lactation, this traditional assumption may well be quite untrue. An extra 250 kcal/d in pregnancy is equivalent, in an adult man, to an increase of only about 0.15 × BMR, an increase that may well be needed at peak agricultural activity; in the child, the energy requirement for growth becomes very small after six months.
A second general point is that many of the processes measured during pregnancy and lactation show a range of variations between individuals which is much greater than that of most biological functions. For example, in one study the maternal weight gain in pregnancy had a coefficient of variation of 100%. Therefore, average results, if applied to individuals, may be very greatly in error.
Thirdly,
although the studies of energy requirements of pregnancy and
lactation presented at this meeting were done in two
industrialized and five Third World countries (The Gambia,
Thailand, Philippines, Mexico and Egypt), none of the populations
studied are from countries characterized by extreme poverty.
2.1. New information
2.2. Policy implications
2.3. Needs for research
The multicenter study
described earlier in this volume has shown that in industrialized
countries the average cost of pregnancy, at about 60,000 kcal, is
not very different from the estimate in the 1985 report. In Third
World countries, the cost was somewhat lower. In theory, the
extra cost of 60,000 kcal should require an extra daily intake,
averaged over the whole of pregnancy, of about 200 kcal. In the
majority of the studies reported here (and, indeed, in as many
others), an increase of this magnitude has not been found, in
spite of extremely careful repeated measurements of food intake.
Energy storage on a constant intake must be balanced by decreased expenditure. There are four possibilities:
1. Decrease in basal metabolic rate (BMR): In all the studies reported at the meeting, individual variations were wide but, except in The Gambia, BMR was found to increase, particularly in the third trimester.
2. Decreases in diet-induced thermogenesis (DIT): The contribution from this source cannot be very important, as DIT accounts for only about 5% of total energy expenditure.
3. Changes in behavior and activity pattern leading to an overall decrease in physical activity. Some evidence for this was found, amounting to about one third of the energy cost of pregnancy.
4. Reduction in the energy cost of physical activities. Evidence was obtained of a decrease of the order of 5% in the cost per kg of activities such as stepping and walking. However, because of the increase in body weight, there was no net saving in energy. It is not clear whether this improvement in what may broadly be called efficiency, results from training, ergonomic factors or biochemical metabolic changes.
1. In the types of populations that have been studied, the incremental energy requirements of pregnancy may be somewhat lower than the 1985 estimates, but we need not be unduly concerned if intakes are somewhat lower than those previously recommended.
2. Changes in behavior and in the pattern of physical activity during pregnancy should not be regarded as socially undesirable.
1. The data from existing studies should be examined to identify, if possible, factors that determine the extremes of individual variations and their associations.
2. More longitudinal information is needed about BMR and fat mass in the prepregnant state and in the first trimester.
3. The preliminary evidence obtained so far on a decrease in physical activity in pregnancy needs to be strengthened by measurements of total energy expenditure with doubly-labelled water. Studies of this kind are already under way in Thailand and in the Philippines.
4. If a decrease in total energy expenditure is found, it is necessary to examine whether this response has any drawbacks for the individual, family or community.
5. Studies should be undertaken in clearly undernourished populations.
3.1. New information
3.2. Policy implications
3.3. Needs for research
In the last few years,
there have been many studies of breast milk output with
doubly-labelled water and test-weighing procedures that take
better account of cultural factors in the family. The main
conclusions are:
1. Contrary to existing belief, if allowance is made for the weight of the baby, the milk output of women in developing countries, or of socioeconomically disadvantaged women, is as great as that of more privileged women, i.e., 750-800 mL/d.
2. Except in very high parity women, there is no evidence that milk output is limited by the secretory capacity of the breast.
3. In the populations that have been studied, there is no evidence that altering the energy intake of the mother affects the total energy output in breast milk.
4. One of the most important variables controlling milk output is the infant's weight.
5. It can no longer be assumed that maternal fat stores laid down during pregnancy are available or drawn upon for the support of lactation.
1. Lactation is a process which concerns the infant as well as the mother. Policies for the promotion of breast-feeding should try to ensure that lactation is adequate not only for normal growth in the normal infant, but for catch-up growth by the low birth-weight baby or the baby exposed to infections.
2. The recommendations in the 1985 report of extra energy intake by the mother to support the cost of lactation should be maintained. If fat stores cannot be drawn upon, the increments in intake may need to be even greater.
3. To the extent that the energy intake from breast milk in developing, countries may be greater than previously supposed, it will be appropriate to postpone the introduction of supplementary feeding.
4. Programs for the supplementary feeding of mothers are unlikely to be an effective mean of increasing breast milk output.
1. Studies on lactation, using modern methods, should be replicated in populations more severely deprived than those studied so far.
2. More work is needed on the physiology and biochemistry of milk production and secretion, in order to get a better understanding of the controlling factors.
3. The reason needs to be investigated, why supplementation of the mother apparently has different effects in pregnancy and in lactation.
4. Research is needed on energy expenditure in lactating women. Does the mother economize, as she apparently does in pregnancy ?
5. If reductions in the amount and changes in the pattern of energy expenditure do occur during lactation, their social implications must be examined.
6. Further research is needed on the effect on breast milk output of supplementary feeding of the infant, in terms of amount and timing.
4.1. Energy supply and physical growth of infants and children
4.2. Energy supply and physical activity of children
4.3. Chronic energy deficiency and development
4.4. Causes of inadequate energy intakes in children
Since children have not
been discussed at this workshop they are considered here only
very briefly.
1. Recent studies of energy intake in exclusively breast-fed children indicate that their energy requirements, as judged by growth, can be met by much lower intakes than those proposed in the 1985 report, which were based on the observed intakes of formula-fed infants.
2. Information about the BMR of infants and young children is consistent and satisfactory, but very little is known about their levels of physical activity. To fill this gap, more work is needed on instruments for investigating activity in young children. This subject is one of high priority.
3. A great deal remains to be learned about the relation between energy supply and amount and pattern of growth. Decreased growth in length compared with international references (stunting) is extremely common in developing countries. Factorial estimates of the nutrient requirements of children are all based on increments in weight. It is a tenable hypothesis, based on some supportive evidence, that growth in length is determined by the supply of protein or of factors associated with protein in foods, and that growth in weight is determined by growth in length, in order to maintain body composition.
4. Therefore, more studies are needed of the relationships between the intakes of energy and nutrients and the amount and pattern of growth. Such studies are particularly illuminating if they compare groups with different dietary patterns and are particularly important for children below three years. A number of valuable studies of this kind were done in the 1970s, but they seem to have fallen from favor. A major difficulty was that many children are still partially breast-fed at 2-3 years of age, so that accurate estimates of intakes were virtually impossible. This problem could now be overcome by using heavy water.
There is some recent
evidence that, when the energy intake of children is inadequate,
before growth falls off, there is a decrease in physical
activity. This is to be regarded as highly undesirable, because
it limits the child's exploration of the environment and the
development of social relationships.
There are numerous anecdotal accounts of apathy, with-drawnness, failure to make friends, etc. - effects that may produce a progressive handicap throughout life.
These
considerations reinforce the need for studies on the physical
activity of children in relation to energy intake and the
development of appropriate methodology.
Analysis of the effects of
chronic energy deficiency on the child's development is
complicated by the fact that it is associated with many other
handicaps of poverty.
Small body size from infancy and childhood and low weight-for-height maintain low but statistically significant correlations (.20-.30) with both comparatively low intelligence test scores and poor school achievement. These correlations are consistent across low-income populations in developing countries and are reasonably explained by the effects of nutritional history. However, these correlations do not explain the nature of the relationships between undernutrition and brain function; they are only a reflection of a possible bi-directional effect of a history of undernutrition.
Small body size and low weight-for-height have also been associated with low activity levels among infants and young children.
There is no single definitive work that has tested adequately the developmental impact of supplementation in early life. The data that exist point out that, among nutritionally-at-risk populations, supplementation has a mild but important beneficial effect on mental and social-emotional development during infancy and the preschool years. Likewise, supplementation increases activity level among nutritionally at risk infants and children.
In comparison to the effects of nutritional supplementation the effects of multifocal interventions (i.e., supplementation, health, education) are substantively greater. These beneficial effects are apparent even if the intervention begins after the first three years of life or passed the so-called critical period of brain growth.
Research needs in this area may be summarized as follows:
1. Determine the social environmental and health factors that increase the probabilities of developmental deviations among nutritionally-at-risk infants and children.
2. Determine the nature of activities that are particularly vulnerable under conditions of chronic energy deficiency.
3. Determine the cost to cognitive and social-emotional development of maintenance of energy balance by reduced activity among infants and children.
4. Establish the educational effects of undernutrition during the school period.
If the consequences
discussed above are to be prevented, it is necessary to know why
energy intakes fall below what is necessary or desirable. There
are various possible causes:
1. Absolute lack of available food, e.g., during the hungry season. It is known that in such cases catch-up growth can occur when food supplies improve (Nepal). The question arises as to whether "stop-and-go" growth carries any handicap compared with more regular growth.
2. Even though food is available, the child may not be able to eat enough of it, because of low energy density, too widely spaced meals, etc.
3. Factors that influence the mother's activity may reduce the time available for cooking and child care.
4. Infections have a profound impact on appetite and energy intake.
The
relative importance of different causes of low energy intakes of
children will differ in different environments. A high priority
should be given to in-depth case studies of families in different
communities. The number of families studied need not be large.
Where this approach has been used, it has proved extremely
cost-effective.
As the questions raised and
the proposals for further work have implications for public
health policy, IDECG should give priority to organizing a
workshop to examine all aspects of the relation between energy
intake and physical activity in children, including methodology,
causes, short- and long-term effects.