Unfortunately, the research isn’t as clear when it comes to what happens after your crash diet, says Johannsen. For instance: Why do some people gain the weight back and others don't? And what about your hormones and insulin sensitivity? Here’s what ~could~ happen, based on what research has been done so far:
Your metabolism might be all wonky.
This drops a lot during a crash, and there’s some data to suggest that this persists even after you go back to a normal diet, says Johannsen. That means you’d be eating more calories and still burning fewer, which would obviously lead to weight gain.
Your insulin sensitivity (and risk of diabetes) might be impacted.
The initial drop in weight might improve your insulin sensitivity temporarily, but researchers don’t know what effect repeated crash diets could have on it in the long run, says Johannsen.
Fat might come back faster than muscle does.
Remember how crash diets burn through your muscle tissue? Well, they might not bounce right back after the crash. “Your body’s first impetus is to rebuild the fat stores,” says Johannsen. So when you come off the crash diet, your body will want to store fat before it works on rebuilding your muscles. Because life isn’t fair.