They've typically still lost fat though, even if they've gained weight. I don't know what sort of stats there are comparing those who've lost weight and succes

They've typically still lost fat though, even if they've gained weight. I don't know what sort of stats there are comparing those who've lost weight and successfully kept it off (for, say, 10 years or so) via exercise/sports vs via dieting alone, though from what I know it's a pretty low percentage that do manage in the latter group. My understanding is that the initial weight loss is primarily down to diet changes, but exercise works better at helping maintaining a healthier weight/lifestyle.