A slow, low-intensity run uses more fat for fuel but takes longer to burn a lot of calories in total. That’s why it’s advised to run longer than 30 minutes when running at a low-intensity. However, a faster, high-intensity run can burn more calories in a shorter time period. And even if just a small percentage of those calories come from fat, it can still significantly boost your weight loss!
At its core, burning fat comes down to the process of lipolysis—the breaking down of fat lipids, explains Seedman. This happens in the mitochondria of the muscles, or the powerhouses of the cells, responsible for generating the energy our cells need to do their jobs. Exercise has been shown to improve mitochondria function, which then promotes fat breakdown, Seedman adds. Plus, working out helps regulate pretty much all the hormones that optimize fat loss.
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