Researchers have often noted that people who exercise more frequently gain less weight over time. There’s a seemingly straightforward explanation for this: They’re burning more calories, so they remain in energy balance. This is probably at least partially correct, but there may be more to the story, as Barry Levin’s research suggests. His findings show, not surprisingly, that exercise attenuates weight gain in rats when they’re offered a fattening diet.107 Yet Levin’s data also reveal that fit rats aren’t just leaner—they actively defend a lower adiposity set point than sedentary rats on the
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