Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of interventional trials
PubMed 27609363 · doi:10.1017/S0007114516003160
What was done
A systematic review and meta-analysis of trials evaluated the metabolic effects of aerobic exercise (duration ≤120 min) performed in the fasted versus fed state in adults. Databases (PubMed, Scopus, Cochrane) were searched through July 2016. Outcomes evaluated were fat oxidation during exercise and plasma concentrations of insulin, glucose, and NEFA before and immediately after exercise. Results were pooled as weighted mean differences (WMD) with 95% confidence intervals.
What was found
Across 27 included studies (273 total participants), fat oxidation during exercise was significantly higher in the fasted compared with the fed state (WMD -3.08 g; 95% CI -5.38, -0.79; I² = 39.1%). NEFA concentrations did not differ significantly between states (WMD 0.00 mmol/l; 95% CI -0.07, 0.08; I² = 72.7%). Plasma glucose (WMD 0.78 mmol/l; 95% CI 0.43, 1.14; I² = 90.8%) and insulin concentrations (WMD 104.5 pmol/l; 95% CI 70.8, 138.2; I² = 94.5%) were significantly higher when exercise was performed in the fed state.
Why it matters
This meta-analysis demonstrates that fasting prior to aerobic exercise under two hours acutely enhances whole-body fat oxidation compared to exercising after a meal.
Limits
The total sample size is small across 27 trials (273 participants, averaging ~10 per study). Substantial statistical heterogeneity was observed for NEFA (I² = 72.7%), glucose (I² = 90.8%), and insulin (I² = 94.5%). The abstract does not report participant demographics, sex, training status, or long-term clinical outcomes like weight loss or chronic metabolic adaptations.
Cited by
- supports Exercising in a fasted state enhances fat oxidation both during exercise and throughout the day.
- supports Training in a fasted state increases fat oxidation compared to training in a fed state.