Examining changes in respiratory exchange ratio within an 8‐week weight loss intervention

Background Maintaining weight loss is difficult, partly as a result of accompanying reductions in fat oxidation. The present study examined fat oxidation [reflected by respiratory exchange ratio ( RER )] within an 8‐week, self‐led weight loss intervention. Changes in RER , body fat ( BF %) and estimated energy expenditure ( EE ) were examined. Methods Twenty‐two adults [13 females, nine males; mean (SD) age 34.6 (16.5) years; body mass index 32.0 (4.3) kg m −2 ] received a self‐directed workbook; twelve were also randomised to receive a self‐monitoring wrist‐worn device. At weeks 0 and 8, RER (indirect calorimetry), BF % (BodPod) and estimated EE [7‐day physical activity recall (PAR‐EE) were collected. Participants were pooled and paired t ‐tests were used to examine changes over time. Correlations explored associations among variables. Participants were then dichotomised into weight loss group ( WL ) or weight stable/gainers group ( WSG ) and eating behaviours [Intuitive Eating Scale ( IES ‐2)] were examined by 2 × 2 repeated measures multivariate analysis of covariance . Results There were no significant changes in RER , body fat percentage and PAR ‐ EE . A significant negative association was found between week 8 PAR ‐ EE and week 8 RER , as well as between BF % change and RER change. There was a significant time by WL versus WSG group effect of IES ‐2 scores, with the WL group self‐reporting significantly increased scores in Eating for Physical Reasons rather than Emotional Reasons ( EPR ) subscale. Conclusions Increased physical activity after an 8‐week weight loss intervention was associated with a higher fasting fat oxidation. Participants who increased EPR scores were more successful in weight loss than those without a change in this subscale.