|Social Policy Report, Volume X, Number 5, 1996 (Society for Research in Child Development, 1996, 32 pages)|
|Reconceptualizing the relationship of nutrition and development|
Protein and energy. In the 1960s, when researchers and policymakers were becoming increasingly concerned that early PEM could result in permanent impairment of intellectual development, it was widely accepted that protein was the limiting nutrient in the diet of populations at risk. During the next decade, however, dietary energy was held to be the more critical factor (McLaren, 1974). It was understood that to provide undernourished children with protein without also providing sufficient energy was futile, because the dietary protein would be used to supply energy rather than essential amino acids.
Iron, iodine, and zinc. Accompanying the new focus on energy was a recognition that, in most circumstances, energy deficiency may be closely linked to political and socioeconomic problems not easily addressed by simple nutritional intervention. Such political complexity and the fact that dietary energy is inextricably confounded with a mix of nutrients were two of numerous reasons that led subsequent research and policy interest to shift from the study of PEM effects to the effects of specific nutrients, especially Vitamin A, iron, iodine, and zinc. Whereas iron deficiency was known to be a cause of anemia, zinc deficiency a cause of growth retardation, and iodine deficiency a cause of goiter and cretinism, studies established further that deficiencies in these nutrients have broader systemic effects that lead to multiple threats to child health and development (United Nations ACC/SCN, 1993).
Complexities of deficiencies. Mild-to-moderate protein-energy malnutrition is difficult to diagnose, because it does not produce a specific set of symptoms and signs. It also coexists with other nutrient deficiencies. The same foods, particularly those from animal origin (from meat, fish, and poultry), are often sources of energy, protein, and distinct micronutrients (e.g., iron and zinc). Children that do not have access to these foods are at risk of multiple nutritional deficiencies. Further, some constituents of a habitual diet can limit the absorption of some important nutrients. This is the case, for example, with phytates, tea, and coffee which inhibit the absorption of non-heminic iron. Dietary quality2 is critically important, requiring diversity and, to the extent possible for a family, the inclusion of foods of animal origin.
Where food is scarce and dietary quality is poor, diets consist primarily of staples such as cereals and legumes. Such diets typically contain few animal products, fresh fruits, or vegetables, and are therefore associated with low intakes of certain vitamins and minerals, high intakes of phytates and fiber, and poor bioavailability3 (Allen, 1993). Moreover, bioavailability is reduced when the supply of nutrients that enhance absorption is low. Finally, when food availability and quality are inadequate, the incidence of morbidity is usually high, with several nutrients simultaneously depleted through anorexia, malabsorption, and/or diarrhea with its associated inflammatory responses (Chen, 1983; Martorell & Yarbrough, 1983; Sahni & Chandra, 1983).
Thus, with both the nature of nutritional deficiency and the relationship among nutrients unclear, it remains a challenge not only to understand effects but to utilize findings in designing intervention strategies. In populations where general undernutrition is common, supplementation with a single nutrient, with the exception perhaps of iodine, will often be ineffective because as one deficiency is ameliorated, others may become limiting.