Exercising in the Fasted State Reduced 24-Hour Energy Intake in Active Male Adults.
Level 2 - randomized trial
Randomized counterbalanced crossover trial in humans.
PubMed 27738523 · doi:10.1155/2016/1984198
What was done
Twelve active white males (age 20.8 ± 3.0 years, VO2max: 59.1 ± 5.7 mL/kg/min) completed a randomized, counterbalanced crossover study. In one condition, participants fasted before running for 60 minutes at 60% VO2max (NoBK), and in the other, they consumed breakfast before running (BK). All food intake was weighed and measured for 24 hours. Blood glucose and hunger were assessed across 5 time points, and respiratory quotient (RQ) was measured during exercise.
What was found
Total 24-hour energy intake was significantly lower in NoBK than BK (15312 ± 4513 kJ vs. 19172 ± 4542 kJ; p < 0.001). Evening energy intake was also significantly lower in NoBK (10833 ± 4065 kJ vs. 12265 ± 4278 kJ; p = 0.039). Exercise RQ was significantly lower in NoBK (0.86 ± 0.03 vs. 0.90 ± 0.03; p < 0.001), reflecting greater fat oxidation. Pre-exercise blood glucose was lower in NoBK than BK (4.5 ± 0.6 vs. 5.2 ± 0.7 mmol/L; p = 0.025). Hunger was significantly lower in BK before exercise, after exercise, and before lunch, though blood glucose and hunger were not associated with energy intake.
Why it matters
Skipping breakfast prior to moderate-intensity morning exercise acutely reduced daily energy intake without causing subsequent compensatory overeating, alongside increasing exercise fat oxidation.
Limits
The study was limited to a very small sample (n = 12) of young, active white males, preventing generalization to women, older adults, or sedentary/clinical populations. Only acute 24-hour intake was measured, leaving long-term energy balance and body composition effects unaddressed.
Cited by
- partial Exercising in a fasted state enhances fat oxidation both during exercise and throughout the day.