The immediate postpartum period is recognized as a special time in many societies and is commonly associated with food and work restrictions. The logic of food restrictions during a period of increased energy and protein needs has been challenged, but few data are available to test the impact of these practices on the diets of lactating women. In the eastern Amazon the immediate postpartum period is referred to as resguardo, lasts for 40-41 days and includes food taboos and work restrictions. Taking a biocultural perspective, this paper combines data on the beliefs and attitudes surrounding the practice of resguardo with quantitative data on the actual dietary intakes and activity patterns of a cohort of 23 lactating women followed from birth through 15 months postpartum. This paper addresses three topics: (1) shared ideals regarding resguardo; (2) adherence to food and work restrictions; and (3) the impact of these practices on women's dietary intakes and energy expenditure. The results show that the majority of women adhered to food taboos and work restrictions. During resguardo energy expenditure in physical activity was lower, reducing women's energy needs and allowing them to devote more time to infant care. However, energy intakes were also lower. The reduction in dietary intake was impacted more by work restrictions and the loss of women in subsistence tasks during resguardo than by adherence to food taboos. In addition to altering maternal energetic strategies, resguardo served an important social function by reinforcing bonds and, for young women, marking the transition to womanhood.