When people exercise but eat enough to match the calories they burn, their bodies do not enter a state of net fat loss over 24 hours, regardless of whether they are lean, obese, or trained athletes.
Mechanism
Synthesis from 1 study
After you exercise and eat, your body releases insulin to manage the food, and that insulin stops fat from being released from your fat stores. Even though you burned calories, there’s not enough fat in your blood to burn, so your muscles use sugar instead — meaning you end up storing more fat than...
Most probable mechanism
When you eat after exercising, your 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 your muscles end up burning sugar instead. This means your body stores more fat than it burns over the next day, even if you ate exactly what you burned during exercise (10.1152/japplphysiol.00958.2009).
Consumption of meals after exercise triggers pancreatic beta-cell secretion of insulin in response to elevated blood glucose, resulting in sustained postprandial insulin elevation (10.1152/japplphysiol.00958.2009).
Elevated insulin binds to receptors on adipose tissue cells, activating signaling pathways that inhibit hormone-sensitive lipase, thereby suppressing lipolysis and reducing the release of free fatty acids into the bloodstream (10.1152/japplphysiol.00958.2009).
Plasma free fatty acid concentrations remain suppressed below fasting levels throughout the waking period due to persistent insulin action, limiting the primary exogenous fuel source available for skeletal muscle oxidation (10.1152/japplphysiol.00958.2009).
Skeletal muscle shifts substrate utilization toward carbohydrate oxidation due to restricted fatty acid availability, preventing any net increase in 24-hour fat oxidation despite increased energy expenditure from exercise (10.1152/japplphysiol.00958.2009).
The net result is a more positive 24-hour fat balance, meaning fat storage exceeds fat oxidation, even when energy intake matches expenditure during exercise in lean sedentary, obese sedentary, and lean endurance-trained individuals (10.1152/japplphysiol.00958.2009).
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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