Variation in Maternal Strategies During Lactation: The Role of the Biosocial Context

Compared to other mammals, human milk is dilute which lowers the relative daily cost of lactation allowing women greater flexibility in the strategies they use to meet the energy demands of lactation. These strategies include increasing dietary intake, reducing energy expenditure, and drawing on energy stores. Women are affected by the biosocial context in which they live, including norms regarding the sexual division of labor and diet and activity patterns during lactation, as well as household-level factors such as economic strategy and the availability of social support. This paper combines longitudinal data on dietary intake, energy expenditure, and body weight of 23 lactating Amazonian women living in a subsistence-based economy with detailed ethnographic data and considers how adherence to the cultural norms and the availability of social support contributed to intra-population variation in maternal energetic strategies. Dietary intake was found to vary more than energy expenditure. Adherence to dietary restrictions during the postpartum period of resguardo significantly reduced intra-population variation in energy intake. Women with social support came closer to achieving energy balance during resguardo (t = 2.8; P = 0.01) and peak lactation (t = 2.7; P = 0.02) and lost less weight (t = 3.6; P = 0.002) than those without such support. Those with social support had higher energy (t = 2.1; P = 0.05) and carbohydrate (t = 2.1, P = 0.05) intakes during resguardo and spent significantly less time in subsistence work during peak (t = 2.6, P = 0.03) and late lactation (t = 2.4, P = 0.03). Case studies are used to place these finding in context. Am. J. Hum. Biol. 21:817-827, 2009. (C) 2009 Wiley-Liss, Inc.