One hour of moderate exercise does not lead to increased fat burning over the next 24 hours if you are not in a calorie deficit, regardless of whether you are lean or obese and whether you are...
Mechanism
Synthesis from 1 study
After eating, insulin rises and stops fat from being released from fat stores, so even if you exercise, there isn't enough fat in your blood to burn — your body just uses sugar instead. This is why one hour of exercise doesn't lead to more fat burning over the next day if you eat enough to replace...
Most probable mechanism
When someone eats after exercising, their body releases insulin to handle the food, and this insulin shuts down the release of fat from fat stores. Even though exercise burns energy, there isn't enough fat in the blood to burn because insulin keeps blocking its release, so the body ends up using sugar instead. This means no extra fat is burned over the next day, even if the person worked out — as shown in 10.1152/japplphysiol.00958.2009.
Consumption of meals triggers pancreatic beta-cell secretion of insulin in response to elevated blood glucose, maintaining postprandial insulin levels above fasting thresholds throughout the waking period, even on exercise days.
Elevated insulin binds to insulin receptors on adipocytes, activating signaling pathways that inhibit hormone-sensitive lipase (HSL), thereby suppressing the breakdown of stored triglycerides into free fatty acids.
Reduced lipolysis decreases the release of free fatty acids (FFA) from adipose tissue into circulation, maintaining plasma FFA concentrations below levels required to support increased fat oxidation demands during and after exercise.
Low circulating FFA limits the primary exogenous fuel source available for skeletal muscle oxidation, forcing a shift toward carbohydrate utilization despite increased energy expenditure from exercise.
Skeletal muscle oxidation of carbohydrates increases while fat oxidation remains unchanged or decreases, resulting in no net increase in 24-hour fat oxidation and a more positive fat balance, indicating fat storage rather than loss.
Evidence from Studies
Supporting (1)
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When energy balance is maintained, exercise does not induce negative fat balance in lean sedentary, obese sedentary, or lean endurance-trained individuals.
Contradicting (0)
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