Beneficial metabolic adaptations due to endurance exercise training in the fasted state.
Level 2 - randomized trial
Controlled trial comparing fasted versus fed endurance training
PubMed 21051570 · doi:10.1152/japplphysiol.00907.2010
What was done
Twenty young male volunteers completed a 6-week cycling training program (1-1.5 h/day at ~70% VO2max, 4 days/week) while consuming isocaloric carbohydrate-rich diets. Half trained in the fasted state (F; n = 10), and half ingested carbohydrates before (~160 g) and during (1 g·kg⁻¹·h⁻¹) training sessions (CHO; n = 10). Outcomes measured included VO2max, 60-minute time-trial performance, and metabolic responses (intramyocellular lipid breakdown, enzyme activities, fat oxidation, and blood glucose) during a 2-hour fasted cycling bout at ~65% pretraining VO2max.
What was found
Both groups showed identical increases in VO2max (+9%) and 60-minute time-trial performance (+8%) (P < 0.01). However, F increased the exercise intensity corresponding to maximal fat oxidation (+21%) more than CHO (+6%) (P < 0.05). Maximal citrate synthase (+47%) and β-hydroxyacyl coenzyme A dehydrogenase (+34%) activities increased significantly in F (P < 0.05) but not in CHO. Exercise-induced intramyocellular lipid breakdown increased in type I fibers (P < 0.05) and tended to increase in type IIa fibers (P = 0.07) in F, with no change in CHO. Only F prevented an exercise-induced drop in blood glucose (P < 0.05).
Why it matters
Training in the fasted state stimulates superior muscular oxidative and lipid metabolism adaptations compared with fed training, even though short-term performance gains remain similar.
Limits
The sample size was small (n = 20) and included only young males. Randomization was not explicitly stated in the abstract. Test exercise was performed exclusively in the fasted state, which may favor the group accustomed to fasted training.
Cited by
- supports Aerobic endurance training performed in a fasted state yields greater training adaptations compared to training in a fed state.