Experimental Design
In the mid-1960s, protein deficiency was seen as the most important nutritional problem facing the poor in developing countries, and there was considerable concern that this deficiency affected children’s ability to learn. The Institute of Nutrition of Central America and Panama (INCAP) was the locus of a series of studies on this subject, leading to the implementation of a nutritional supplementation trial that began in rural eastern Guatemala in 1969. Two sets of village pairs (one pair of “small” villages with about 500 residents each and another pair of “large” villages with about 900 residents each) - similar in terms of a variety of nutritional, social, and economic outcomes – were identified as sites for the study. Two of the villages, one from within each pair matched on population size were (based on a coin flip) randomly assigned to receive as a dietary supplement a protein-energy drink called atole. In the remaining villages, an alternative supplement, fresco, was provided. Several micronutrients (iron, thiamine, riboflavin, niacin, ascorbic acid, and vitamin A) also were added to both atole (which already had some) and fresco, in amounts that yielded equal concentrations across the supplements per unit of volume. The nutritional supplements (i.e., atole or fresco) were distributed in each village in centrally-located feeding centres and were available twice daily, to all members of the village on a voluntary basis, for two to three hours in the mid-morning and two to three hours in the mid-afternoon, times selected to be convenient to mothers and children, but that did not interfere with usual meal times. All residents of all villages also were offered high quality curative and preventative medical care, free of charge throughout the intervention. Preventative services, including immunization and antiparasites campaigns, were conducted simultaneously in all villages. To ensure that the results were not systematically influenced by the characteristics of the health, research, or survey teams, all personnel were rotated periodically throughout the four villages.
From 1969 to 1977, INCAP implemented the nutritional supplementation trial and medical care. While the supplement was freely available to all village residents (as described above), the associated observational data collection focused on pregnant and lactating women and children between zero and seven years of age at any point during the intervention period. For children, exposure to the atole supplement was a function of location and birth year.