I’VE ALWAYS SUSPECTED THAT A LOT OF THE MIDDLE-AGED METABOLIC “SLOWDOWN” IS JUST INACTIVITY: Metabolism doesn’t slow down until senior years, researchers say. “veryone knows that your metabolism peaks in your teenage years, when you’re fit and active and feeling your oats. And everyone knows that a person’s metabolism slows down in middle age, as bodies start to expand and sag, and become less energetic. But that’s all wrong, it now appears to have been fake news about how humans age that’s gained the currency of truth over the years.”