Energy balances of healthy Dutch women before and during pregnancy: limited scope for metabolic adaptations in pregnancy.

To investigate changes in energy metabolism during pregnancy, complete 8-d energy balances were measured before pregnancy and at 12, 23, and 34 wk gestation in 12 healthy Dutch women. While for each individual woman experimental diets were kept constant throughout the study with average intakes of 8.76 +/- 0.92 MJ/d (before pregnancy), 8.72 +/- 1.08 MJ/d (week 12), 8.85 +/- 0.93 MJ/d (week 23), and 8.72 +/- 1.12 MJ/d (week 34), neither the digestibility nor the metabolizability of the supplied diets showed significant changes from before pregnancy (92.8% and 88.6%, respectively) throughout pregnancy (92.7% and 88.2%, respectively). Twenty-four-hour energy expenditure (24-h EE) increased significantly from 8.63 +/- 0.80 MJ/d (before pregnancy) to 8.73 +/- 1.15, 9.08 +/- 1.08, and 9.94 +/- 0.94 MJ/d in weeks 12, 23, and 34 of gestation, to the extent predictable from changes in resting metabolic rate so that in an experimental setting with physical activity and energy intake standardized there seems little scope for other adaptive mechanisms.