Relationships Between Body Weight, Training Statuses And Metabolic Flexibility In Male And Female Adults

PURPOSE: Using data from two RCTs, we aimed to explore the effects of adiposity and training status on metabolic flexibility (MF),i.e. the ability for the body to adjust fuel oxidation to changes in fuel availability and energy demand. METHODS: Healthy female and male adults who were lean and inactive or trained (Ln-inactive/ Ln-trained, BMI = 19-25 kg/m2), inactive and with obesity (Ob-Inactive, BMI = 30-40 kg/m2), or weight reduced and inactive or trained (RO-inactive/-trained, BMI = 25-40 kg/m2, lost >10% body weight) were recruited. Ln-trained, Ln-inactive, and Ob-Inactive completed 3 conditions consisting in a 24 h stay in a whole-room calorimeter (WRC) during which participants were rested and fed with low-fat (20% fat, LF-EB) or high-fat (60%fat, HF-EB) diet or asked to perform a 30-min moderate intensity exercise and fed LF diet while been in energy balance (EX-EB). Ln-Inactive, Ob-Inactive, RO-Trained and RO-Inactive completed a 24 h stay in the WRC during which they were asked to either rest (REST-EB) or complete an acute exercise tailored to create 15% of energy deficit (EX-ED). Differences between night RQ and day RQ (ΔRQ) and the variances(VAR) in 24 h RQ and insulin were used as indices of MF. Linear mixed-models with group, condition, and group-by-condition as fixed effects, and subjects as random effect were used. RESULTS: ΔRQ (LSMeans ± SE, 0.040 ± 0.016, p = 0.02) and 24 h RQ VAR (0.895 ± 0.345, p = 0.02) were greater and 24 h In VAR (0.65 ± 0.13 p < 0.001) was lower in response to HF-EB compared to LF-EB in all groups. However, EX-EB did not elicit any difference in ΔRQ, 24 h RQ VAR, 24 h insulin VAR in any of the groups.ΔRQ (-0.010 ± 0.002, p < 0.001) and 24 h RQ VAR (-0.189 ± 0.098,p = 0.062) were lower and 24 h insulin VAR (0.098 ± 0.113, p = 0.394) was greater in EX-ED than in REST-EB. 24 h insulin VAR denoted group effects, Ob-Inactive displayed a greater 24 h VAR than both Ln-Inactive (-1.852 ± 0.366,p < 0.0001) and RO-Inactive (-0.872 ± 0.397, p = 0.04). CONCLUSION: When EB is maintained, an acute dietary challenge is better for testing MF than an acute exercise bout. However, coupling acute exercise with energy deficit allows to detect between-group differences in MF. People with obesity are less flexible than lean ones, and people who lost weight and trained have a better MF than those who dieted alone.