Metabolic, endocrine and appetite responses to carbohydrate versus niacin ingestion during exercise in healthy females and males.

BACKGROUND: The substrates used during exercise may influence the post-exercise response of systemic metabolites and hormones, along with the drive to refeed following exercise. However, no study has assessed whether manipulating substrate metabolism during exercise independent from carbohydrate ingestion alter these responses. OBJECTIVE: To assess the effects of niacin and carbohydrate ingestion during exercise on post-exercise metabolite and hormone concentrations, and ad libitum energy intake. METHODS: Fifteen participants (five female) performed one hour of cycling at 95% lactate threshold1 with carbohydrate ingestion (CARB, insulin-induced lipolysis suppression), niacin ingestion (NIACIN; insulin-independent lipolysis suppression) and fasted (FAST), in a crossover design with blood and breath samples. Two hours after exercise, energy intake was measured at an ad libitum meal. The study was registered on clinicaltrials.gov/study/NCT05417659. RESULTS: Compared with FAST, CARB and NIACIN suppressed plasma NEFA concentrations during exercise (time x condition: p<0.001) and total fat oxidation (mean±95%CI; CARB: -11±4 g, p<0.001; NIACIN: -9±5 g, p=0.001). CARB and NIACIN increased plasma GLP-1TOTAL concentrations compared to FAST (time x condition interaction: p<0.001), with the highest concentrations in CARB (p<0.001 vs FAST and NIACIN). There was no evidence of differences in ad libitum energy intake between conditions (FAST 833 ± 206 kcal, CARB 786 ± 219 kcal, NIACIN 780 ± 158 kcal: p=0.37). Ketone body and (large) very-low-density lipoprotein-triglyceride (VLDL-TG) concentrations were lower with NIACIN vs FAST (time x condition: both p<0.001), whereas branched-chain amino acid (BCAA) concentrations were lower with CARB vs FAST (time x condition: p<0.001). CONCLUSIONS: These data demonstrate that niacin ingestion increases carbohydrate oxidation during exercise and post-exercise GLP-1, ketone body and VLDL-TG concentrations but does not seem to detectably influence post-exercise energy intake. This suggests that manipulating fatty acid availability during exercise may have greater implications for metabolism than for energy balance behaviours.