The Effect Of Fasted Cycling Exercise At Different Times Of The Day In Overweight Individuals

Abstract

Intermittent fasting has become an increasingly popular intervention for metabolic health. Combining intermittent fasting with exercise may lead to benefits for weight management. PURPOSE: To investigate the effect of fasted exercise at different times of the day on metabolic responses and appetite regulation in overweight males. METHODS: Twelve healthy males (Mean ± SD; age 26 ± 4 y; body fat 23 ± 2%) completed four, 60 min cycle ergometry trials at 60% V̇O2peak in a randomised order; in the morning fasted (AMFAST), evening fasted (PMFAST) and after consuming a breakfast meal in the morning (AMFED) and evening (PMFED). Circulating levels of ghrelin, glucagon-like peptide-1 (GLP-1), pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), insulin, triglycerides, non-esterified fatty acid (NEFA), glucose, and cholesterol were measured at baseline, post-breakfast, pre-exercise, post-exercise, pre-soup ingestion, then every 30 min post soup-ingestion for 2 h. Appetite was assessed at 15 min intervals throughout. Substrate utilisation was measured every 30 min and continuously throughout exercise. RESULTS: Area under the curve (AUC) values for NEFA were greater in PMFAST compared to all trials (186.5 ± 46.3 vs. AMFAST 120.5 ± 42.6, AMFED 80.8 ± 23.8, PMFED 91.1 ± 36.4 mmol/L 4.75 h; P<0.05). AMFAST NEFA was also greater than AMFED (P=0.029). AUC values were greater for GLP-1 in AMFED trial compared to PMFAST (8660.2 ± 12232.5 vs 5967.0 ± 12027.5 mmol/L 4.75 h, P<0.05), and PP values for PMFED greater compared to all trials (155411.9 ± 86064.1 vs. AMFAST 90165.4 ± 90145.6, AMFED 107162.5 ± 72846.2, PMFAST 105364.0 ± 81320.2 mmol/L 4.75 h, P<0.05). A time of day effect was seen for cholesterol with PM greater than AM (P<0.05). Fat oxidation was greater during AMFAST and PMFAST exercise compared to FED trials (P<0.05). Ratings of appetite did not change between trials once all participants consumed the lunch meal post exercise (P>0.05). No differences were seen in AUC between trials for ghrelin, PYY, glucose or insulin. CONCLUSION: Fasted exercise elicited greater NEFA responses, and some appetite hormones appear to respond differently to varying exercise conditions and time of day in overweight males. Regardless of the time of day, fasted exercise favours fat metabolism and may induce a short-term negative energy balance.