For people trained in endurance sports, exercising after eating does not lead to greater fat burning over 24 hours, because the rise in insulin after eating reduces the amount of free fatty acids...
Mechanism
Synthesis from 1 study
When endurance-trained people eat before or after exercising, insulin rises and stops fat cells from releasing fat into the blood — so even though their muscles are ready to burn fat, there’s not enough fat available, and they end up burning carbs instead. This is why their total fat burning over...
Most probable mechanism
When endurance-trained people eat before or after exercising, their body releases insulin to handle the food’s sugar. This insulin tells fat cells to stop releasing stored fat into the blood, so there isn’t enough fat available for muscles to burn, even though the person is working out and their body is good at burning fat. As a result, the body ends up burning more carbs instead, and overall fat burning over the whole day doesn’t go up — this is shown in 10.1152/japplphysiol.00958.2009.
Consumption of meals triggers pancreatic beta-cell secretion of insulin in response to elevated blood glucose, resulting in sustained postprandial insulin elevation above fasting levels throughout the waking period.
Elevated insulin binds to insulin receptors on adipocytes, activating signaling pathways that inhibit hormone-sensitive lipase (HSL), thereby suppressing lipolysis and reducing the breakdown of stored triglycerides into free fatty acids.
Reduced lipolysis leads to sustained suppression of plasma free fatty acid (FFA) concentrations, which remain below fasting levels for hours after meals, limiting the primary exogenous fuel source for skeletal muscle oxidation.
Low circulating FFA availability forces skeletal muscle to prioritize carbohydrate oxidation over fat oxidation during and after exercise, overriding the enhanced fat-burning capacity of endurance-trained individuals.
The shift in substrate utilization prevents a net increase in 24-hour fat oxidation, resulting in unchanged or more positive fat balance despite increased energy expenditure from exercise.
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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