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At 9 wk postpartum the difference in energy intake of 40 lactating (2440 +/- 430 kcal/d) and 16 nonlactating women (1680 +/- 400 kcal/d) was 760 kcal/d but decreased to 550 kcal/d when adjusted for habitual intakes and body weight. Energy cost of lactation amounted to 650 kcal/d (breast-milk production, 745 +/- 130 g/d). When compared with nonlactating counterparts, the lactating women mainly achieved energy balance by eating more. Sixteen of the 40 lactating women were also studied at 56 wk. Their cost of lactation at 5-13 wk was 630 kcal/d (breast-milk production, 720 +/- 124 g/d); these women met their energy cost of lactation by eating more (415 kcal/d); by tissue mobilization (35 kcal/d), and by reducing energy expenditure (180 kcal/d). The present study helps in the understanding of how well-nourished women with an adequate lactational performance may cope in everyday life with the energy stress of lactation, and suggests that current recommendations of energy needs during lactation are too high.

Body weight, fat mass, and basal metabolic rate were measured longitudinally from early pregnancy until 2 mo postpartum in 57 healthy Dutch women; 23 of whom were also studied before pregnancy. Weight gain over pregnancy was 11.8 +/- 3.7 kg and weight gain from 12 wk gestation to delivery was 10.3 +/- 3.8 kg. Birth weights and placental weights were 3458 +/- 527 and 657 +/- 114 g, respectively. Gain in maternal fat stores over pregnancy was 2.0 +/- 2.6 kg and difference in fat mass from 12 wk gestation to 5 wk postpartum was 1.2 +/- 2.2 kg. The energy equivalent of the gain in fat stores, including costs of synthesizing, can be estimated as 22,000 kcal. The cumulative increment in basal metabolism over pregnancy was 34,350 +/- 30,000 kcal. When the energy equivalent of the gain in tissue other than fat stores is assumed to be approximately 11,750 kcal, total energy cost of pregnancy is at 68,100 +/- 38,560 kcal.

Basal metabolic rate (BMR), activity pattern, and energy costs of some daily activities were measured in 25 Dutch women throughout pregnancy and the first year postpartum. Physical activity index (PAI), which refers to daily energy expenditure expressed as a multiple of BMR, was calculated from activity-pattern data and activity costs. Mean PAIs (+/- SD) throughout pregnancy, during the first 6 mo postpartum, and at 1 y postpartum were 1.48 +/- 0.08, 1.49 +/- 0.07, and 1.53 +/- 0.10 X BMR, respectively. Because measured BMR at 1 y postpartum was 1440 +/- 168 kcal/d, costs for physical activity in pregnancy and the first 6 mo postpartum were, respectively, approximately 70 and approximately 50 kcal/d lower than at 1 y postpartum. For women with sedentary lifestyles the energy saved during pregnancy and lactation because of decreased physical activity and decreased costs of activities will be limited.

Body weight, basal metabolic rate (BMR), and treadmill metabolic rate (TMR) (3.9 km/h, no elevation) were measured in 39 women at 12, 24, and 36 wk gestation and at 9 wk postpartum. Prepregnancy measurements were also made on 15 of the women. TMR at 36 wk (3.65 +/- 0.50 kcal/min) was significantly higher than at 24 wk (3.38 +/- 0.43 kcal/min) or at 9 wk postpartum (3.38 +/- 0.43 kcal/min). Net energy cost (TMR minus BMR) at 36 wk gestation (2.42 +/- 0.40 kcal/min) was not different from prepregnancy or postpartum values but was significantly higher than at 12 wk (2.28 +/- 0.39 kcal/min) and 24 wk (2.28 +/- 0.37 kcal/min) gestation. In eight women the energy cost of self-paced walking on a treadmill was measured. The absolute and net energy cost decreased sharply from 6 to 12 wk gestation (by 8% and 11%, respectively) but remained unchanged afterwards. The data suggest that in the energy requirements for pregnant women no additional allowance need be made for physical activity, even if a woman's activity pattern includes a substantial amount of externally paced work.