|Chronic Energy Deficiency : Consequences and Related Issues (International Dietary Energy Consultative Group - IDECG, 1987, 201 pages)|
|A critical view of three decades of research on the effects of chronic energy malnutrition on behavioral development|
For the purposes of this paper, a developmental risk factor was defined (see footnote 1) as a circumstance or event occurring in an early life period that increases the probability of diverting a child's growth and developmental trajectory from a course typically followed by children when physiological and emotional needs are met. Although the main-effect model has failed to give a conclusive answer to the issue of whether or not early undernutrition is a developmental risk factor, the evidence on the synergism between undernutrition and social-environmental factors strongly supports this contention. Through its interactions with illness and adverse family and socioeconomic conditions, undernutrition increases the probability of diverting the trajectory of mental development, a hazard not encountered by other children living under similar environmental and economic conditions who do not experience undernutrition. Moreover, and perhaps more importantly, undernutrition shapes behavioral adaptation into forms that are different from those of well-nourished children.
The evidence also points in the direction of research that integrates nutritional variability and context along a time dimension. Endemic infant and childhood malnutrition is a tragic manmade condition that provides a unique natural experiment to understand the biological basis of human behavior. Behaviorally-oriented research among chronically undernourished children has generally defined this condition as a biological insult, disregarding the behavioral implications of its long-term effects on the energy balance equation. A likely outcome of low energy expenditure, to maintain homeostasis, is reduction in activity, an important component of the behavioral repertoire of infants and young children (GOLDSMITH et al., 1987). As such, low energy expenditure is likely to shape interactions between the organism and the immediate environment (GRAVES, 1976, 1978; RICCUTI, 1981; BEATON, 1983; VALENZUELA and ARAYA, 1987), it would be of particular developmental interest to determine the ways in which the undernourished organism establishes transactions12 with caretakers, that is, the ways in which the energy-deficient child influences behaviors of "others" so that the energy demands are in keeping with its energy balance.
12 For present purposes I use the term
transaction following RUTTER's definition (1983): "Transactional effects differ
from all the interaction effects considered thus far in that it is not a
question of one variable potentiating, reducing, or altering the effect of some
other variable or outcome, but rather of one variable changing the other"
On the other hand, if research interest stems from consideration of applied issues (public health) then the greatest payoff lies in questions aimed at identifying and operationalizing those environmental factors that, in conjunction with undernutrition, increase children's developmental risk. Evidence from research on other biological risk factors suggests that cumulative risk through the additive and interactive effects of social and biological risk factors in time might be the best predictor of final outcome. Accordingly, there could be significant public health payoff in the identification of family or community "risk" variables13.
13 These could be conceptualized as
time-independent or time-dependent. The former refers to structural variables,
such as parental illiteracy, which are not likely to change throughout the
child's infancy and early childhood. Time-dependent variables vary as the child
grows older. These variations could occur in a systematic way. For example,
rainy seasons with higher demands on maternal work could be considered a
time-dependent variable that varies systematically within a 12-month period and
represents a growth risk to infants and young children (ADAIR and POLLITT,
1985). Increases in family size do not follow a specific schedule; they
generally result in caretaking practices within the household which could have
adverse consequences for young children.
A recognition that it is necessary to change from bivariate to multivariate models is not a guarantee that the main effect model and bivariate equations will not be the prescriptions used in research on undernutrition and behavioral development. It does, however, provide a conceptual umbrella to understand better the developmental meaning of the data that are generated from research with different conceptual and methodological approaches.