When energy balance is maintained, exercise does not induce negative fat balance in lean sedentary, obese sedentary, or lean endurance-trained individuals.
Level 3 - non-randomized controlled study
Controlled cross-over physiological trial without explicit mention of randomization in the abstract
PubMed 19833807 · doi:10.1152/japplphysiol.00958.2009
What was done
The study evaluated the acute effects of 1 hour of stationary cycling at 55% of aerobic capacity (EX) versus a sedentary control day (CON) on 24-hour fat oxidation and fat balance while maintaining strict 24-hour energy balance. Participants were 27 men and women across three groups: lean sedentary (LS, n = 10, BMI 22.5 ± 6.5 kg/m²), lean endurance-trained (LT, n = 10, BMI 21.2 ± 1.2 kg/m²), and obese sedentary (OS, n = 7, BMI 35.5 ± 4.4 kg/m²). Twenty-four-hour energy expenditure, substrate oxidation, glucose, insulin, and free fatty acid (FFA) profiles were measured in a metabolic chamber.
What was found
Twenty-four-hour fat oxidation did not significantly differ between CON and EX days in LS (43 ± 9 vs. 29 ± 7 g/day), LT (53 ± 8 vs. 42 ± 5 g/day), or OS (58 ± 7 vs. 80 ± 9 g/day). However, 24-hour fat balance was significantly more positive on the EX day compared to CON (P < 0.01). Twenty-four-hour glucose, insulin, and FFA profiles were similar on EX and CON days, with FFA concentrations remaining below fasting levels following the first meal.
Why it matters
This paper demonstrates that when the calories expended during exercise are replaced to maintain energy balance, acute exercise does not increase 24-hour fat oxidation. It indicates that overall energy balance, rather than exercise per se, dictates daily fat balance.
Limits
The sample size was small (total n = 27, including only 7 obese participants), and the abstract does not state whether the order of conditions was randomized. Measurements were limited to a single acute 24-hour eucaloric window, so the findings cannot be directly extrapolated to chronic exercise training or hypocaloric conditions.
Cited by
- supports Acute fat oxidation during or immediately after exercise does not meaningfully offset 24-hour total energy metabolism to produce greater long-term body fat loss.