Additional energy requirements for term pregnancies are traditionally estimated as 1200 kJ/d or 325 MJ. These estimates approximate measured energy costs for well-nourished women, but non-Western populations subsisting on limited diets have much lower expenditures. Based on recent studies of energy expenditure during pregnancy, this paper reviews the 1) association between gestational weight gain and fat gain, 2) the influence of maternal energy status on basal metabolic energy expenditure in late pregnancy, and 3) potential energy metabolism adaptations available to pregnant women and how adaptations vary with energy status. Available data suggest that additional energy requirements during pregnancy vary from 0 to 500 MJ and depend on maternal energy status. If energy supplies are limited, adaptations spare energy for fetal growth; if energy is abundant, energy balance may be achieved in different ways depending on individual behavioral changes in food intake or activity patterns and on adjustments in basal metabolism or fat deposition.