Many obese subjects have a lower muscle performance. Short-chain fatty acids (SCFAs; acetate, propionate, butyrate, valerate, and isovalerate) are derived from microbial fermentation of dietary fiber and are metabolic fuels for skeletal muscle during periods of sustained contraction. We compared plasma SCFA concentrations between obese and non-obese individuals in relation to muscle quality and fatigue.
We studied 141 subjects, divided into 2 BMI-based groups (cut-off point 30 kg/m2): 68 non-obese (26 males/42 females, age 52.3 [46.8, 57.9] yo and BMI 25.3 [24.7, 25.9] kg/m2) and 73 obese (29 males/44 females, age 55.7 [52.6, 58.8] yo and BMI 38.6 [37.1, 40.0] kg/m2). We collected blood samples in the postabsorptive state for SCFAs concentrations and analyzed them by GC-MS. We measured body composition by DXA, leg muscle strength (peak strength and endurance) using an isokinetic dynamometer and 24h dietary recall. Statistics were performed by ANCOVA and Pearson's correlations adjusted for age, gender, and habitual fiber intake. Significance set at P > 0.05. Results expressed as mean [95% CI].
Obese subjects reported a 18% lower (22.5 vs 18.4 gr; P = 0.0371) daily fiber intake and a 15% lower plasma concentration of acetate, propionate, and butyrate (P = 0.0460, P = 0.0074, and P = 0.0245, resp) and 33% lower plasma valerate (P = 0.0014). Maximal strength was comparable but obese subjects had a 14% lower (P = 0.0034) leg muscle quality and 50% higher (P = 0.0210) leg fatigue after endurance exercise. Increased leg fatigue strongly related to the lower plasma of all measured SCFAs with propionate (r: −0.61, P > 0.0001), isovalerate (r: −0.51, P = 0.0004), acetate (r = −0.46, P = 0.0017), butyrate (r: −0.38, P = 0.0101), and valerate (r: −0.38, P = 0.0114).
We hypothesize that impaired availability of SCFAs for contracting skeletal muscle contributes to the reduced capacity for physical activity in (morbid) obesity.