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Association of resting energy expenditure with fat gain during pregnancy

      Related article, page 445
      Gestational weight gain (GWG) outside the current Institute of Medicine guidelines
      Institute of Medicine/National Research Council (Committee to Reexamine IOM Pregnancy Weight Guidelines, Food and Nutrition Board and Board on Children, Youth, and Families)
      is a common occurrence: 47% of women gained above the guidelines and 23% below them in a recent systematic review and meta-analysis that included 1.3 million women.
      • Goldstein R.F.
      • Abell S.K.
      • Ranasinha S.
      • et al.
      Association of gestational weight gain with maternal and infant outcomes: a systematic review and meta-analysis.
      Compared with gaining within these guidelines, this analysis showed that gaining either above or below them is associated with a higher risk of adverse outcomes for mothers and their infants.
      • Goldstein R.F.
      • Abell S.K.
      • Ranasinha S.
      • et al.
      Association of gestational weight gain with maternal and infant outcomes: a systematic review and meta-analysis.
      Clinicians and researchers have long focused on limiting GWG, beginning as early as possible during gestation. Although there are effective interventions that reduce the risk of excessive GWG by 20%,
      • Muktabhant B.
      • Lawrie T.
      • Lumbiganon P.
      • Laopaiboon M.
      Diet or exercise, or both, for preventing excessive weight gain during pregnancy (Review).
      the amount of weight change produced by these interventions is lower than the amount needed to assure that the majority of women gain within the guidelines.
      • Thangaratinam S.
      • Rogozińska E.
      • Jolly K.
      • et al.
      Effects of interventions in pregnancy on maternal weight and obstetric outcomes: meta-analysis of randomised evidence.
      To understand why it has been difficult to develop fully effective interventions, it is useful to consider the physiological basis for GWG. It consists of the products of conception as well as gains in maternal water, fat-free mass, and fat mass. The gain in fat mass during pregnancy is highly variable and strongly positively associated with total GWG.
      • Butte N.F.
      The increase is fat mass is of particular concern because it is difficult to lose, and if it is not lost postpartum, it contributes to the development of obesity and its associated health problems later in women’s lives.
      Interventions to help women gain within the guidelines usually focus on moderating dietary intake, increasing physical activity, or both. Current recommendation recognize that dietary intake should increase during the second and third trimesters of pregnancy.
      Adequate physical exercise is also recommended during pregnancy,
      American College of Obstetricians and Gynecologists
      Exercise during pregnancy and the postpartum period. ACOG Committee opinion no. 267.
      but pregnant women usually reduce their activities during pregnancy and, for the same activities, expend less energy doing them.
      • Lof M.
      • Forsum E.
      Activity pattern and energy expenditure due to physical activity before and during pregnancy in healthy Swedish women.
      However, physical activity is not the major component of women’s total energy expenditure during pregnancy,
      • Forsum E.
      • Lof M.
      Energy metabolism during human pregnancy.
      so it makes sense to consider the largest component, at 60%, of energy expenditure during pregnancy, namely resting energy expenditure (REE) (also known as basal metabolic rate).
      In this edition of the Journal, Berggren et al

      Berggren EK, O'Tierney-Ginn P, Lewis S, Presley L, Haugel de-Mouzon S, Catalano PM. Variations in resting energy expenditure: impact on gestational weight gain. Am J Obstet Gynecol 2017;217:445.e1-6.

      report the results of a secondary analysis of their own prospective data on healthy women who were studied before conception and again at 34–36 weeks of gestation. The authors sought to examine how REE changed during pregnancy and how this change was related to GWG and changes in body composition. This study included 51 healthy women with a mean body mass index of 23 kg/m2 and an average age of 32 years, who were studied between 1985 and 1998. Of these women, 96% were white, 80% were parous, and 20% were overweight.
      A high proportion of the parous subjects had been recruited to the original study because they had had gestational diabetes mellitus in a previous pregnancy.
      • Catalano P.M.
      • Tyzbir E.D.
      • Wolfe R.R.
      • et al.
      Carbohydrate metabolism during pregnancy in control subjects and women with gestational diabetes.
      • Catalano P.M.
      • Roman-Drago N.M.
      • Amini S.B.
      • Sims E.A.
      Longitudinal changes in body composition and energy balance in lean women with normal and abnormal glucose tolerance during pregnancy.
      None of the subjects was diabetic before conception, but 37% of them developed gestational diabetes mellitus during the study pregnancy.
      During their pregnancies, fat mass increased 30%, with 30% variation among the subjects. In contrast, fat-free mass (FFM) increased 19%, with only 6% variation. To adjust for the variation in FFM, which contains metabolically active tissue (muscle), the authors expressed REE in 2 ways: as kilocalories per kilogram of FFM per day and as kilocalories per day.
      From before conception to late pregnancy, Berggren et al

      Berggren EK, O'Tierney-Ginn P, Lewis S, Presley L, Haugel de-Mouzon S, Catalano PM. Variations in resting energy expenditure: impact on gestational weight gain. Am J Obstet Gynecol 2017;217:445.e1-6.

      found that REE (expressed as kilocalories per kilogram of FFM per day) increased 11% on average but actually decreased during this period for 25% of the subjects. The women whose REE decreased did not differ from those in whom REE increased in body composition, dietary intake, or leisure-time activity. Expressed this way, REE measured late in pregnancy was significantly and negatively correlated with change in fat mass in late pregnancy and GWG.
      When REE was instead expressed as kilocalories per day, it increased 13% from before conception to late pregnancy. Before conception and late in pregnancy, REE was significantly and positively associated with the change in FFM from before conception to late pregnancy.
      The authors used their data to illustrate that women with similar GWG values could differ remarkably in their pregnancy-related change in REE (expressed as kilocalories per day) and, correspondingly, pregnancy-related fat gain. This observation helps to explain why some women have more difficulty than others in losing the weight that they gained while pregnant.
      The findings reported by Berggren et al

      Berggren EK, O'Tierney-Ginn P, Lewis S, Presley L, Haugel de-Mouzon S, Catalano PM. Variations in resting energy expenditure: impact on gestational weight gain. Am J Obstet Gynecol 2017;217:445.e1-6.

      are useful clinically because they illustrate that the change in REE is significantly related to GWG and change in fat mass during pregnancy. The authors argue that interventions could be developed to tailor recommendations for dietary intake to women’s needs based on REE measured in clinical settings.
      Although obtained some time ago, the data analyzed by Berggren et al

      Berggren EK, O'Tierney-Ginn P, Lewis S, Presley L, Haugel de-Mouzon S, Catalano PM. Variations in resting energy expenditure: impact on gestational weight gain. Am J Obstet Gynecol 2017;217:445.e1-6.

      contribute to the limited number of studies about pregnancy-related changes in REE and fat mass that include preconceptional measurements of these factors.
      The results of the study add to our understanding of these biological relationships. However, these findings are generalizable only to healthy white women, so further work is required to extend these findings to women of other racial/ethnic groups or women with obesity. Although it may be possible to measure REE in some clinical settings, this procedure is not widely available. The findings from this study that suggest that pregnant women with low REE values or low changes in REE values may be at risk of excessive fat gain, but further research is needed to understand how the data on REE could be used to develop effective means of limiting excessive fat gain during pregnancy.

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      Linked Article

      • Variations in resting energy expenditure: impact on gestational weight gain
        American Journal of Obstetrics & GynecologyVol. 217Issue 4
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          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.
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