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

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.

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.

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.

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.