INTRODUCTION Nutritional health research has traditionally focused on nutrient type and quantity. More recently, studies have investigated the concept of chrononutrition, the influence of nutrient timing. Mice fed in a daily time-restricted feeding (TRF) window gain less weight and display improved glucose tolerance (1). Results in humans are mixed, with daily TRF improving indices of whole-body insulin sensitivity of overweight men with pre-diabetes (2) and reducing fasting concentrations of glucose, insulin and triglycerides in healthy men (3). AIMS Primary: Assess whether TRF improves whole-body and skeletal muscle insulin sensitivity in healthy young men. Secondary: Assess changes in body composition and energy balance in response to TRF. METHODS The energy intake (EI) and expenditure (EE) of eight healthy males [Age 22 (2) years, BMI 24.1 (2.0) kg.m-2; mean (SD)] was assessed for one week of habitual diet (baseline) and two weeks of TRF. During TRF, participants fasted daily between 4pm-8am and subcutaneous glucose monitoring was performed throughout. Participants consumed a standardised evening meal ~12h before visiting the laboratory prior to and immediately after TRF, to assess their metabolic response to a liquid test meal (1g/kg/BW dextrose and 0.4g/kg/BW protein) using the arterio-venous forearm balance model. DEXA scans, indirect calorimetry measurements and fasted and postprandial vastus lateralis biopsies were also obtained. RESULTS Daily feeding periods decreased by an average of 5.5h during TRF and EI was reduced by ~400 kCal (t-test; p<0.01). Total EE did not change, resulting in a mean body mass loss of 1kg (t-test; p<0.01). TRF had no effect on fasting blood glucose concentrations but 24h continuous glucose monitoring revealed consistently lower blood glucose levels during the fasting phase of TRF (throughout the night) compared with the baseline period. There was an increase (t-test; p<0.05) in the Matsuda index (a composite of hepatic and peripheral insulin sensitivity), primarily driven by a reduction in postprandial insulin responses (ANOVA; p<0.05), indicating an improvement in whole-body insulin sensitivity post-TRF. Forearm (muscle) glucose uptake was higher (ANOVA; p<0.05) in the first 90 min after ingestion of the test meal, indicating an improvement in local muscle insulin sensitivity. Forearm branched chain amino acid (BCAA) uptake was also higher post-TRF (ANOVA; p<0.01) but no changes in lean body mass (LBM) were found. CONCLUSION TRF leads to favourable metabolic adaptations in healthy individuals including enhanced whole-body and skeletal muscle insulin sensitivity. Persistent elevations in BCAA uptake over longer periods of TRF may lead to better maintenance of LBM under conditions of significant weight loss.