activity or thermogenesis along with high variability in BMR during pregnancy, that offering prescriptive energy intake recommendations would be impractical because it is impossible to know how an individual woman’s metabolism will respond.
Durnin (1991) reported on longitudinal changes in energy expenditure during pregnancy among Scottish and Dutch women. Among this cohort, an increase in BMR was not seen until 16 weeks’ gestation and was followed by a mean increase of 400 kcal/day over pregravid BMI. The total energy cost of pregnancy was estimated at 69,000 kcal. Adjusting for dietary energy intake (~22,000 kcal) the authors estimated that decreased physical activity or increased efficiency of work accounted for an additional savings of ~47,000 kcal. Similarly Forsum et al. (1985) found an increase in BMR throughout gestation in a study of Swedish women.
Lawrence et al. (1985) studied how women in a developing country responded to increasing food intake during pregnancy. Pregnant women in the Gambia who followed their normal dietary pattern experienced energy sparing of 11,000 kcal with no increase in BMR above pregravid BMI until 30 weeks’ gestation. Further, the women showed a mean GWG of 6 kg with no increase in adipose tissue mass. When their baseline diet was supplemented with 723 kcal/day in additional food, BMR increased by approximately 1,000 kcal over pregravid BMI. Women whose diets were supplemented with additional food had a mean 8 kg increase in GWG and a 2 kg increase in fat mass. Food supplementation had no effect, however, on the energy cost of activity and did not result in increased birth weight when physical work was decreased.
Goldberg et al. (1993) used the doubly labeled water method (International Dietary Energy Consulting Group, 1990) to assess BMR, energy intake, and body composition in 12 affluent women at pre-conception and at 6-week intervals from 6 through 36 weeks’ gestation. Estimated changes in BMR, TEE, and fat deposition were 112 ± 104 MJ, 243 ± 279 MJ, and 132 ± 127 MJ, respectively. The mean total energy cost of pregnancy calculated from BMR, TEE, and energy deposited as fat was 418 ± 348 MJ. The women’s self-reported energy intake however was only 208 ± 272 MJ, a significant underestimate of the calculated additional energy cost of pregnancy. Again, the variability in the individual biological response shown in this study supports the impracticality of prescriptive recommendations for energy intake during pregnancy.
A similar prospective study by Butte et al. (2004) of measured energy expenditure in women by prepregnant BMI showed that women in the highest BMI group accumulated greater fat mass (8.4 kg) compared to those in the low BMI group (5.3 kg). The increase in fat mass accounted for most of the variance in total weight gain among BMI groups. In both the low and high BMI groups mean TEE decreased in the second trimester but in-