Propensity for adverse pregnancy outcomes in African-American women may be explained by low energy expenditure in early pregnancy

Abstract

Background: African-American (AA) women have poorer pregnancy outcomes, and studies in nonpregnant women suggest a different etiology of weight gain in AA compared with white women. We hypothesized that physiologic factors such as low energy expenditure and physical activity would be present in AA compared with white women in pregnancy.

Objective: We aimed to identify physiologic risk factors for disordered energy balance in AA and white women early in pregnancy.

Design: This was a cross-sectional study in 66 pregnant women with obesity, between 14 and 16 wk of gestation. Energy intake was calculated using the intake-balance method. Energy expenditure was measured in free-living conditions [total daily energy expenditure (TDEE)] over 7 d with the use of doubly labelled water and during sleep [sleeping EE (SleepEE)] in a room calorimeter. Body composition was measured by air displacement plethysmography and physical activity by accelerometers. Markers of metabolic health were obtained from fasting blood and urine.

Results: AA (n = 34) and white (n = 32) women were comparable in age (mean ± SEM: 27.7 ± 0.6 y), enrollment body mass index [mean ± SEM (in kg/m2): 36.9 ± 0.7], and body fat (mean ± SEM: 45.0% ± 0.6%). AA women had more fat-free mass (P = 0.01) and tended to be more insulin-resistant (homeostasis model assessment of insulin resistance, P = 0.06). Energy intake was significantly lower in AA than in white women (2499 ± 76 compared with 2769 ± 58 kcal/d, P = 0.001), although absolute TDEE was comparable (AA: 2590 ± 77 kcal/d; white: 2711 ± 56 kcal/d; P = 0.21). After adjusting for body composition, TDEE was significantly lower in AA women (-231 ± 74 kcal/d, P = 0.003), as was SleepEE (-81 ± 37 kcal/d, P = 0.03). Physical activity, substrate oxidation, and metabolic biomarkers (triiodothyronine and thyroxine concentrations, catecholamine excretion) were not significantly different between groups.

Conclusions: Body mass-adjusted energy expenditure is significantly lower in AA than in white pregnant women. Energy intake recommendations for pregnancy do not consider this difference and may therefore overestimate energy requirements in AA women. This may lead to unintentional overeating and contribute to the disparity of excess gestational weight gain and postpartum weight retention that is more prevalent in AA women. This trial was registered at clinicaltrials.gov as NCT01954342.

Figures

FIGURE 1

Comparison of energy intake and EE between AA and white women in early pregnancy. Data are presented as means ± SEMs. (A) Energy intake was calculated by the intake-balance method, combination between doubly labeled water and changes in fat-free and fat mass (AA: n = 26; white: n = 31); and macronutrient composition using food photography (AA: n = 25; white: n = 26). (B) EE was measured over 7 d using doubly labeled water (TDEE) and once overnight (0200–0500) in whole-room calorimetry (SleepEE). *Significant difference in total energy intake between AA and white women (P < 0.05), whereas macronutrient composition was comparable between the groups. AA, African American; EE, energy expenditure; SleepEE, sleeping energy expenditure; TDEE, total daily energy expenditure.

FIGURE 2

Comparison of EE adjusted for body composition between AA and white pregnant women with obesity. Each data point represents 1 participant, and the lines are means ± SEMs. Residual EE reflects the difference between the EE predicted from a regression equation and EE that was measured. Correlations between fat-free mass and energy expenditure (A: TDEE; C: SleepEE) and the associated regression lines are shown for AA (TDEE: n=32; SleepEE: n=33; filled circles, straight lines) and white (TDEE: n=32; SleepEE: n=31; open circles, dotted lines) women separately, because for both TDEE and SleepEE, we observed a main effect for race and no race × FFM interaction. The main effect for race on TDEE (B) and SleepEE (D) is represented as residual EE, which reflects the difference between the EE predicted from a regression equation (EE as dependent of fat-free mass and fat mass) and measured EE. AA, African American; EE, energy expenditure; SleepEE, sleeping energy expenditure; TDEE, total daily energy expenditure.

FIGURE 3

Comparison of physical activity between AA and white pregnant women with obesity. Each data point represents 1 participant, and the lines are means ± SEMs. The regression line (in A) is shown for all AA (n = 31, filled circle) and white (n = 31, open circle) women together, because no main effect for race or race × FFM interaction was observed. (B) AREE reflects the difference between the EE predicted from a regression equation (TDEE as dependent of SleepEE) and measured TDEE. (C) Physical activity level was calculated as the ratio of TDEE to RMR. (D) Steps were measured using SenseWear accelerometers for 24 h (AA: n = 34; white: n = 32). AA, African American; AREE, activity-related energy expenditure; EE, energy expenditure; SleepEE, sleeping energy expenditure; TDEE, total daily energy expenditure.

FIGURE 4

Estimates of TDEE for AA and white women using doubly labeled water and a published maternal energy intake model (19). Data are presented as means ± SEMs, by method of TDEE measurement and race. Estimates for EE are derived from the current maternal energy intake model (Model, grey bars) and from the double isotope dilution method, adjusted for body mass and body composition (Adjusted, black bars). The horizontal lines indicate the overall mean for AA (n = 32) and white (n = 32) women. *Statistically significant difference. Comparisons between AA and white women were analyzed if the interaction term Method × Race was confirmed to be statistically significant (P < 0.05). AA, African American; EE, energy expenditure; TDEE, total daily energy expenditure.