Variations in resting energy expenditure: impact on gestational weight gain

Abstract

Background: There are significant variations in gestational weight gain, with many women gaining in excess of the Institute of Medicine guidelines. Unfortunately, efforts to improve appropriate gestational weight gain have had only limited success. To date, interventions have focused primarily on decreasing energy intake and/or increasing physical activity. Maternal resting energy expenditure, which comprises ∼60% of total energy expenditure compared with the ∼20% that comes from physical activity, may be an important consideration in understanding variations in gestational weight gain.

Objective: Our objective was to quantify the changes in resting energy expenditure during pregnancy and their relationship to gestational weight gain and body composition changes among healthy women. We hypothesized that greater gestational weight gain, and fat mass accrual in particular, are inversely related to variations in resting energy expenditure.

Study design: We conducted a secondary analysis of a prospective cohort studied before conception and late pregnancy (34-36 weeks). Body composition (estimated using hydrodensitometry) and resting energy expenditure (estimated using indirect calorimetry) were measured. The relationship between the changes in resting energy expenditure and gestational weight gain and the change in fat mass and fat-free mass were quantified. Resting energy expenditure was expressed as kilocalories per kilogram of fat-free mass per day (kilocalories per kilogram of fat-free mass^-1/day^-1) and kilocalories per day. Correlations are reported as r.

Results: Among 51 women, preconception body mass index was 23.0 (4.7) kg/m²; gestational weight gain was 12.8 (4.7) kg. Preconception and late pregnancy resting energy expenditure (kilocalories per day) correlated positively with the change in fat-free mass (r = 0.37, P = .008; r = 0.51, P = .001). Late-pregnancy resting energy expenditure (kilocalories per kilogram of fat-free mass^-1/day^-1) was inversely associated with the change in fat mass (r = -0.34, P = .02) and gestational weight gain (r = -0.29, P = .04). From before pregnancy through late gestation, the increase in resting energy expenditure (kilocalories per day) correlated positively with the change in fat-free mass (r = 0.44, P = .002) and negatively with the change in fat mass (r = -0.27, P = .06).

Conclusion: The change in resting energy expenditure from before conception through late gestation correlated positively with changes in fat-free mass but negatively with fat mass accrual. Women with smaller increases in resting energy expenditure across pregnancy had greater gestational weight gain, specifically more adipose tissue. These data suggest that resting energy expenditure is an important factor in gestational weight gain, particularly excess fat mass accrual. Future lifestyle intervention studies need to consider clinically feasible means of estimating resting energy expenditure and, in response, tailor nutrient intake and composition recommendations. Implementing and testing such interventions would be a novel approach to improve compliance with gestational weight gain guidelines.

Keywords: body composition; fat mass; gestational weight gain; indirect calorimetry; maternal fat mass; pregnancy; resting energy expenditure.

Figure 1

Preconception (Pre) to Late Pregnancy (Late) change in resting energy expenditure (REE). A. REE, kcal.kg FFM⁻¹ d⁻¹, red lines with ● represent women with decreased REE across pregnancy, black lines with ▲ represent women with increased REE across pregnancy, *P=0.002; B. REE, kcal/d, *P<0.001

Figure 2

Change in resting energy expenditure (REE) in kcal/day is negatively associated with ΔFM (r=−0.27, p=0.06) and positively associated with ΔFFM (r=0.44, p=0.002); Data for cohort total n=51 were plotted; Representative data from two participants are highlighted; Participant A had a 14.0 kg gestational weight gain, 0.3 kg ΔFM, 13.7 kg ΔFFM, and 749 kcal/day REE increase, illustrated by vertical green line; Participant B had a 13.7 kg gestational weight gain, 2.1 kg ΔFM, 11.6 kg ΔFFM, and 350 kcal/day REE increase, illustrated by vertical red line