Your metabolism isn't broken

This feels true because the weight really does come on easier than it used to. But the part you blamed, your age slowing your engine, is the part the data clears.

When researchers measured total daily energy expenditure with doubly-labeled water across more than 6,600 people in 29 countries, they found that once you adjust for fat-free mass (mostly muscle), metabolism is essentially flat from about age 20 to age 60. It doesn't sag in your 30s. The real decline doesn't begin until about age 60, and even then it's gradual.

So if your metabolism didn't slow, why is the weight easier to gain? Two things changed that you actually control. First, you carry less muscle than you did, because you stopped training and lost some over the years, and less muscle means a lower resting burn. Second, your habits drifted: you move less during the day, you eat a few hundred more calories than you think, you sleep worse. Those are levers. Age is not.

This matters because “my metabolism is broken” is a sentence that ends the conversation. “I carry less muscle and I move less than I think” is a sentence that starts a plan. The first is a life sentence; the second is a to-do list.