title: Respiratory quotient evolution during normal pregnancy: what nutritional or clinical information can we get out of it?
abstract: Food intake increases to a varying extent during pregnancy to provide extra energy for the growing fetus. Measuring the respiratory quotient (RQ) during the course of pregnancy (by quantifying O2 consumption and CO2 production with indirect calorimetry) could be potentially useful since it gives an insight into the evolution of the proportion of carbohydrate vs. fat oxidized during pregnancy and thus allows recommendations on macronutrients for achieving a balanced (or slightly positive) substrate intake. A systematic search of the literature for papers reporting RQ changes during normal pregnancy identified 10 papers reporting original research. The existing evidence supports an increased RQ of varying magnitude in the third trimester of pregnancy, while the discrepant results reported for the first and second trimesters (i.e. no increase in RQ), explained by limited statistical power (small sample size) or fragmentary data, preclude safe conclusions about the evolution of RQ during early pregnancy. From a clinical point of view, measuring RQ during pregnancy requires not only sophisticated and costly indirect calorimeters but appears of limited value outside pure research projects, because of several confounding variables: (1) spontaneous changes in food intake and food composition during the course of pregnancy (which influence RQ); (2) inter-individual differences in weight gain and composition of tissue growth; (3) technical factors, notwithstanding the relatively small contribution of fetal metabolism per se (RQ close to 1.0) to overall metabolism of the pregnant mother.
authors.affiliation: Swiss Federal Institute of Sport Magglingen, Switzerland.
authors.forename: Katarina
authors.initials: K
authors.lastname: Melzer
authors.affiliation: Faculty of Biology and Medicine, Institute of Sports Sciences, University of Lausanne, Lausanne, Switzerland.
authors.forename: Bengt
authors.initials: B
authors.lastname: Kayser
authors.affiliation: Switzerland & Integrative Cardiovascular and Metabolic Physiology, Faculty of Biology and Medicine, Department of Physiology, University of Lausanne, Lausanne, Switzerland. Electronic address: yves.schutz@unifr.ch.
authors.forename: Yves
authors.initials: Y
authors.lastname: Schutz
mesh_terms: D002153:Calorimetry, Indirect; D002245:Carbon Dioxide / Q000378:metabolism*; D002149:Energy Intake; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D005333:Fetus / Q000378:metabolism; D006801:Humans; D010101:Oxygen Consumption / Q000502:physiology*; D011247:Pregnancy / Q000502:physiology*; D011263:Pregnancy Trimester, Third
chemical_list: D002245:Carbon Dioxide
keywords: Energy balance; Energy substrate; Indirect calorimetry; Pregnancy