title: Intra-individual variation in resting metabolic rate during the menstrual cycle.
abstract: Little information exists on the extent of day-to-day intra-individual variation in resting metabolic rate (RMR) in women. The present study has investigated the intra-individual variation in RMR of women during the menstrual cycle. Nineteen women (naturally cycling non-pill users) were recruited to the study. Anthropometric and RMR measurements were taken at least three times per week for the duration of one complete menstrual cycle; measurements were taken for a second, consecutive cycle in eight of the nineteen subjects. RMR was measured by indirect calorimetry using a ventilated hood system under standardized conditions. The measurements made throughout each complete menstrual cycle were averaged and the levels of inter- and intra-individual variation in RMR were assessed by determining the CV (%). Mean RMR of the group was 5686 (sd 674) kJ/d; inter-individual variation in RMR was 11.8 %. There were wide differences in the intra-individual variation in RMR of women (CV range 1.7-10.4 %). The CV in ten subjects was small (2-4 %), while the CV in nine women was high (5-10 %), indicating a significant variation in RMR during the menstrual cycle in certain subjects. Using statistical models, it has been shown that there was a significant effect on RMR due to a subject-specific level of variability; this was the case even when accounting for a possible training effect. In conclusion, the findings from our present study show that RMR cannot be assumed to be 'stable' in all women. The implications of intra-individual variation in RMR and its impact on energy balance needs further research.
authors.affiliation: Nutrition and Food Science Group, School of Biological and Molecular Sciences, Oxford Brookes University, Gipsy Lane Campus, Headington, OX3 0BP. jhenry@brookes.ac.uk
authors.forename: C Jeya K
authors.initials: CJ
authors.lastname: Henry
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Lightowler
authors.forename: Jonathan
authors.initials: J
authors.lastname: Marchini
mesh_terms: D000328:Adult; D001481:Basal Metabolism / Q000502:physiology*; D001835:Body Weight; D002153:Calorimetry, Indirect; D005260:Female; D006801:Humans; D016014:Linear Models; D008597:Menstrual Cycle / Q000502:physiology*