Doctoral Dissertation Improvement: Maternal reproductive trade-offs and the duration of exclusive breastfeeding in a natural fertility population

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International health organizations recommend exclusive breastfeeding for the first 6 months of life to promote optimal infant growth and reduce risk of infectious illness. Globally, however, exclusive breastfeeding for 6 months is relatively rare - including in many less developed populations with high rates of infectious disease. For many mothers, the risks associated with complementary feeding before 6 months of age may not be apparent, or may be outweighed by competing time and energy demands. This study will examine differences in infant feeding patterns and associated outcomes in an economically marginalized population, the Tsimane of Bolivia.This research by doctoral student Melanie Martin (University of California, Santa Barbara), under the supervision of Dr. Michael Gurven, tests the hypothesis that maternal work and childcare demands reduce the length of exclusive breastfeeding. Furthermore, because nursing mothers rapidly lose weight and do not menstruate, Tsimane mothers may introduce complementary foods before 6 months of age to minimize the caloric losses of nursing. This offset may enable postpartum weight maintenance and earlier resumption of menstruation. Tsimane women do not have access to contraceptives; early complementary feeding may therefore contribute to Tsimane mothers' high fertility rates (average 9 children). The researchers will survey Tsimane mothers to determine if the length of exclusive breastfeeding varies with infant condition, maternal age and condition, and maternal work and childcare demands. Researchers will also prospectively collect dietary, behavioral and biological data from Tsimane mothers and infants to examine how complementary feeding patterns affect maternal energy, menstrual status, infant growth and incidence of illness. The study will examine how local beliefs and Tsimane mothers' perceptions of infant health, growth, and development further influence feeding decisions. Results will aid in devising strategies to promote culturally acceptable infant feeding practices that optimally benefit maternal and infant health.