Energy Intake Requirements in Pregnancy

Abstract

Energy intake requirements in pregnancy match the demands of resting metabolism, physical activity, and tissue growth. Energy balance in pregnancy is, therefore, defined as energy intake equal to energy expenditure plus energy storage. A detailed understanding of these components and their changes throughout gestation can inform energy intake recommendations for minimizing the risk of poor pregnancy outcomes. Energy expenditure is the sum of resting and physical activity-related expenditure. Resting metabolic rate increases during pregnancy as a result of increased body mass, pregnancy-associated physiological changes, i.e., cardiac output, and the growing fetus. Physical activity is extremely variable between women and may change over the course of pregnancy. The requirement for energy storage depends on maternal pregravid body size. For optimal pregnancy outcomes, women with low body weight require more fat mass accumulation than women with obesity, who do not require to accumulate fat mass at all. Given the high energy density of fat mass, these differences affect energy intake requirements for a healthy pregnancy greatly. In contrast, the energy stored in fetal and placental tissues is comparable between all women and have small impact on energy requirements. Different prediction equations have been developed to quantify energy intake requirements and we provide a brief review of the strengths and weaknesses and discuss their application for healthy management of weight gain in pregnant women.

Keywords: energy expenditure; energy intake; fetal development; metabolic rate; physical activity; pregnancy.

Figure 1

Appropriate adjustment of energy-expenditure data. (A) The association between body weight and resting metabolic rate is characterized by linear regression (solid line, RMR[kcal/d] = 598 + 11.97 × BW[kg], R² = 0.66) and ratio (pointed line, RMR[kcal/d] = 21.56 × BW[kg], R² = 0.22); of note, logarithmic or polynomial approximations do not improve the prediction of RMR (for both, R² = 0.67). (B) Residual resting metabolic rate (RMR), calculated as measured RMR minus predicted RMR; based on the regression equation in (A); the residuals show no structural over- or underestimate based on body weight. (C) Residual RMR, based on the ratio equation; women with increased body weight have significant lower residual RMR, and would be considered as having a low adjusted metabolic rate.

Figure 2

Total Daily Energy Expenditure during Gestation. Total daily energy expenditure (TDEE) is presented per study and gestational age (GA). The regression line represents the average increase during gestation (TDEE[kcal/d] = 2343 − 1 × GA[weeks] + 0.4 × GA²[weeks], R² = 0.62). Forsum¹ and Forsum² indicate the two different cohorts in the study: both measured before pregnancy, but at different times during gestation; Butte reported the changes in TDEE per BMI class: ‘UW’ indicates underweight: BMI ≤ 19.8 kg/m², ‘NW’ indicates normal weight: BMI 19.8–26 kg/m², and ‘OV/OB’ indicates overweight/obesity: BMI ≥ 26 kg/m².

Figure 3

Resting Metabolic Rate during Gestation. Resting metabolic rate is presented per study and gestational age (GA). The regression line represents the average increase in the resting metabolic rate during gestation (RMR[kcal/d] = 1334 + 10.3 × GA[weeks], R² = 0.55, using non-linear regression (pointed line) did not improve the prediction, R² = 0.57). Forsum¹ and Forsum² indicate the two different cohorts in the study: both measured before pregnancy, but at different times during gestation; Butte reported the changes in RMR per BMI class: ‘UW’ indicates underweight: BMI ≤ 19.8 kg/m², ‘NW’ indicates normal weight: BMI 19.8–26 kg/m², and ‘OV/OB’ indicates overweight/obesity: BMI ≥ 26 kg/m².

Figure 4

Physical activity level during gestation. Physical activity level is presented per study and gestational age (GA). The regression line represents the average decline in the physical activity level during gestation (PAL = 1.68 − 0.0015 × GA[weeks], R² = 0.02). Forsum¹ and Forsum² indicate the two different cohorts in the study: both measured before pregnancy, but at different times during gestation; Butte reported the changes in PAL per BMI class: ‘UW’ indicates underweight: BMI ≤ 19.8 kg/m², ‘NW’ indicates normal weight: BMI 19.8–26 kg/m², and ‘OV/OB’ indicates overweight/obesity: BMI ≥ 26 kg/m².