|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
(Discussion leader K.G. DEWEY, rapporteur B. SCHÜRCH)
When attempting to identify behavioral indicators providing useful information in connection with energy utilization and energy requirements, we are faced with difficult theoretical and methodological problems. Foremost among these is that we should be able to formulate a specific hypothesis explaining how chronic energy deficiency affects behavioral indicators which are valid measures of important elements of a theory of human development. Scientists have worked with apparently attractive constructs which seem to be sensitive to undernutrition, but as long as there is no basis for predicting their significance their inclusion in the study may not be justified. We have, for instance, the construct of mental development and tests developed to measure it which also seem to be sensitive to dietary deficiencies, but the items of these tests were selected for normative reasons, not on the basis of a theory of information processing, learning or development. Thus, we cannot say what functional handicap or risk a score or developmental quotient of a few points below the mean represents.
Ultimately, we should like to know if, to what extent and how energy deficiency affects the social competence of individuals and groups of individuals. Cultural factors play an important role in determining what competences are most important. School performance and achievements have often been used as indicators of social competence in school children and adolescents. It seems much more difficult to define what we mean by social competence in infants and very young children. We do not yet have any test giving a reasonable general representation of cognitive function and information processing during the first two years of life.
One of the main problems in providing evidence of a causal connection between energy deficiency and an outcome variable is the large number of potential confounders. These confounders in combination with ethical restrictions on possible experimental designs, lead to the current situation where, on the one hand, we have a great deal of information on correlations, but on the other practically no evidence showing that modifications in energy availability in a particular population lead to predictable changes in outcome variables that are functionally meaningful.
Given these theoretical and methodological constraints, can we use behavioral indicators to provide general information which complements current theoretical and methodological approaches to establish energy requirements? This may not be completely impossible. At this point in time there seems to be, for instance, a need to look at functional differences between breast- and bottle-fed infants in terms of behaviors, processes and later outcomes. We have the possibility to develop more information on what may be functional deficits of certain population groups, but this information will primarily be of a descriptive nature.
One of the problems we are faced with in doing this kind of assessment is that readily available instruments lack predictive validity. It would, for instance, be useful to have more information on the neurodevelopmental trajectory followed by certain vulnerable groups. But such information, though important, is not likely to tell us anything about future function. The younger the children we wish to examine, the harder it is to find or develop instruments or tests with at least some degree of predictive validity.
What kinds of indicators could provide useful information in connection with activity and energy expenditure variables that are important for the determination of energy requirements? We must look for behaviors likely to be affected when general activity level is reduced. In addition, these should be what Pollitt called "behaviorally meaningful action units". Pollitt's paper suggests that the age at which action units that are indicators of motor development appear, may depend on nutritional status and can be delayed in situations of chronic dietary deficiency. Since motor maturation conditions the ways in which a child interacts with its environment and caretakers, it becomes an element of the whole developmental process and also seems to be related to long-term outcomes.
Growth and development may be delayed by many nutritional and probably also non-nutritional factors. With only one or two exceptions, effects of dietary interventions which have been investigated until now cannot be attributed to changes in dietary energy alone and could be the results of increased intake of one or several nutrients. It has also been shown repeatedly that dietary supplementation and various forms of psychological stimulation can produce very similar improvements in development test scores and growth of underpriviledged young children with deficits in these areas.
The papers and discussions of this workshop have highlighted the fact that infants and children engage in a wide range of activities of widely varying meaning and importance, and that it is important to make a clear distinction between the energy cost and the developmental implications of activity. Physical activities which require a lot of energy often seem to be of relatively little importance from a behavioral and developmental point of view. Yet, it would be desirable to know the extent to which they are affected by energy deficiency and if so, the extent to which their restriction is voluntary.
Other types of activities which are primarily dependent on mental processes could, of course, be affected by energy deficiency as well, and some of these are more likely to have an effect on long-term outcomes that are of functional importance. In this context exploratory behavior, attention span, distractibility and qualitative aspects of play could be useful indicators. Among social transactions in which infants engage, attention-seeking behavior, including crying, may be of particular interest.
If we are interested in effects of energy restriction on physical activity, it is important to determine the extent to which such activity occurs spontaneously and the extent to which it may be encouraged or restricted by caretakers and environmental circumstances. It could, for instance, be imagined that undernourished infants restrict their voluntary activity, but this would be difficult to detect in infants who are carried around all day. In school, children are often not allowed to be as active as they would like to be, and at home too, parents may prefer children who are not disturbing them too much. These are points which also need to be considered in planning and evaluating intervention programs.
A popular hypothesis postulates that energy deficiency reduces a child's overall activity and the extent to which it can explore its environment. Since interactions with persons and objects play an important role in a child's development, this is seen as a possible mechanism explaining the frequently found association of delays in growth and mental development. Some of the information presented at this workshop casts some doubt on the general validity of this hypothesis. We can certainly not equate physical activity and exploration under all circumstances.
Since appropriate measures of activities which appear to be behaviorally meaningful action units have only been developed recently, we do not yet have a sufficient empirical basis to say what activities, when restricted, lead to deficits in exploratory behavior, social interactions, etc., that may have functionally important long-term consequences. We can also not take for granted that the relationships between activity and development are the same in well-nourished and undernourished populations.
Many behavioral aspects of conditions leading to low energy intake seem to merit further study. Dewey mentioned six of these:
1. Child rejection of food. A recent study in Mexico showed that 46 stunted preschool children left behind, on average, 22% of the food made available to them. The percentage of food left behind was the same across the relatively wide range of socioeconomic status among the families studied. It would be of interest to know more about how frequently and why young children reject food.
2. The role of parents and other caretakers in encouraging children to eat. In the United States, parents can often be observed urging their children quite strongly and aggressively to eat more. In busy Third World settings, where parents have so many other things to do, children are often left with a plate of food which, if they do not eat it quickly, gets taken away or is eaten by a domestic animal. In one of Dewey's studies, a positive relationship between encouragement to eat and intake was observed.
3. Interaction of eating frequency and caloric density. In infants and small children, low energy density and bulkiness of the food can limit energy intake, especially when the feeding frequency is low.
4. Children's appetite seems to vary a great deal, and in many instances we are not able to explain why. One of the main problems in investigating this is that we lack a satisfactory operational definition of appetite. We know almost nothing about nutrient deficiencies and metabolic conditions which could lower appetite. There is evidence that a number of deficiencies may have such an effect.
Perceptions of appetite could also vary because of cultural expectations. In certain cultures there could, for instance, be differences between male and female children, males being expected to be more demanding, to request food more often, and when they do not, parental intervention may be more frequent than with girls who may not be subjected to the same expectations.
5. Hyperphagia during catch-up growth after a disease episode has also been found to be very variable. More information is needed on catch-up growth and the factors influencing it. Relatively healthy, breast-fed infants in Davis showed a dramatic increase in dietary intake after infection. More information is needed on catch-up growth and the factors influencing it.
6. Feeding practices during and after illnesses are important because they can modify the impact of morbidity. In breast-fed infants, the intake of breast milk seems more or less protected during illness, whereas the intake of solid foods is decreased. What we do not know is the extent to which this is the result of the infants' voluntary restriction of consumption or due to what the children are offered by their caretakers.