Understanding calorie burning in early pregnancy—moving toward improving health for mothers and children

New research is shedding light on calorie consumption and calorie burning in early pregnancy in women with obesity, which could inform strategies to promote healthy gestational weight gain and reduce racial disparities in pregnancy outcomes. Because of increasing rates of obesity, larger numbers of women than ever before are entering pregnancy with obesity. Pregnant women with obesity are more likely to have excess gestational weight gain. They are also at higher risk of developing other complications, such as gestational diabetes, disorders related to high blood pressure (e.g. preeclampsia) and having a baby with high birth weight. Racial disparities during pregnancy also exist. For example, pregnant African American women are more likely than White women to have complications such as gestational diabetes, preeclampsia, stillbirth, preterm birth, and weight retention after giving birth. In new research, scientists examined calorie (energy) intake and energy expenditure (calorie burning) in early pregnancy in women with obesity to identify factors that could promote healthy pregnancies and reduce racial health disparities.

Researchers studied healthy, pregnant women with obesity from different racial/ethnic backgrounds at 13-16 weeks of gestation. In their first analysis, which included data from 72 women, the researchers sought to identify factors that may influence excess gestational weight gain. They found that 88 percent of participants were sedentary, 12 percent were moderately active, and none were highly active. Furthermore, they found that energy expended during sedentary activities (e.g., rest and sleep) accounted for nearly 70 percent of the women’s daily total energy expenditure, and that energy expenditure from activity (e.g., exercise) was low. The researchers also discovered variability in the rate at which the participants burned calories regardless of their activity level: over a quarter of them had a low metabolic rate, which means they burned fewer calories than women with average or high metabolic rates and thus may have been more susceptible to excess gestational weight gain. Based on the energy expenditure measurements from their experiments, the researchers determined that the number of calories that the women should be consuming to maintain appropriate gestational weight gain was lower than what is estimated based on currently used models; those models were developed based on data primarily from women without obesity. Together, these findings identify three factors that could be contributing to excess gestational weight gain in women with obesity: current recommendations related to caloric intake during pregnancy may overestimate the needs of women with obesity, pregnant women with obesity have low activity levels, and some women have a low metabolic rate.

In their second analysis, which included data from 66 African American and White women, the researchers sought to identify biological factors that predispose African American women to worse pregnancy outcomes. They found that African American women consumed fewer calories than did White women, but there was no racial difference in physical activity levels, which were low in all women. However, after adjusting for individual differences in body weight and body composition (proportions of fat and lean mass in the body), African American women were found to burn significantly fewer calories than White women. Based on that finding and similar to results described in the first analysis, the researchers calculated that current recommendations for caloric intake during pregnancy, which do not differ by race, may overestimate the needs of African American women with obesity. Although studies have shown that African American women do not have higher rates of excess gestational weight gain than White women, it is possible that the lower energy expenditure in African American women may contribute to their higher risk of excess weight retention after giving birth—making it more likely that they will have higher levels of obesity in subsequent pregnancies. Further research to develop interventions to address the newly identified factors associated with energy expenditure during pregnancy, such as personalizing guidelines related to caloric intake and developing strategies to promote physical activity during pregnancy, could help support healthier pregnancies, reduce racial disparities, and improve health outcomes for mothers with obesity and their children.

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