Two weeks of early time-restricted feeding (eTRF) improves skeletal muscle insulin and anabolic sensitivity in healthy men

BACKGROUND: Altering the temporal distribution of energy intake (EI) and introducing periods of intermittent fasting (IF) exert important metabolic effects. Restricting EI to earlier in the day [early time-restricted feeding (eTRF)] is a novel type of IF. OBJECTIVES: We assessed the chronic effects of eTRF compared with an energy-matched control on whole-body and skeletal muscle insulin and anabolic sensitivity. METHODS: Sixteen healthy males (aged 23 ± 1 y; BMI 24.0 ± 0.6 kg·m-2) were assigned to 2 groups that underwent either 2 wk of eTRF (n = 8) or control/caloric restriction(definition) (CON:CR; n = 8) diet. The eTRF diet was consumed ad libitum and the intervention was conducted before the CON:CR, in which the diet was provided to match the reduction in EI and body weight observed in eTRF. During eTRF, daily EI was restricted to between 08:00 and 16:00, which prolonged the overnight fast by ∼5 h. The metabolic responses to a carbohydrate/protein drink were assessed pre- and post-interventions following a 12-h overnight fast. RESULTS: When compared with CON:CR, eTRF improved whole-body insulin sensitivity [between-group difference (95% CI): 1.89 (0.18, 3.60); P = 0.03; η2p = 0.29] and skeletal muscle uptake of glucose [between-group difference (95% CI): 4266 (261, 8270) μmol·min-1·kg-1·180 min; P = 0.04; η2p = 0.31] and branched-chain amino acids (BCAAs) [between-group difference (95% CI): 266 (77, 455) nmol·min-1·kg-1·180 min; P = 0.01; η2p = 0.44]. eTRF caused a reduction in EI (∼400 kcal·d-1) and weight loss (-1.04 ± 0.25 kg; P = 0.01) that was matched in CON:CR (-1.24 ± 0.35 kg; P = 0.01). CONCLUSIONS: Under free-living conditions, eTRF improves whole-body insulin sensitivity and increases skeletal muscle glucose and BCAA uptake. The metabolic benefits of eTRF are independent of its effects on weight loss and represent chronic adaptations rather than the effect of the last bout of overnight fast. This trial was registered at clinicaltrials.gov as NCT03969745.