The science I've read on metabolism is based on lab rats/mice, and it's still an open question about if that applies to humans.
I'm very aware that eating has a significant pyschological component, but, again, if you're going to say "ex-atheletes are often very overweight," I'd like to see studies.
Most animals have something like half a billion heartbeats of life. This can be extended to a billion through limiting diet and sex, or basically asceticism.
It's commonly cited that while athletes' hearts beat faster while exercising, they beat lower the rest of the day, thus giving them fewer beats per year. I'm assuming, though, that most athletes don't swim 6 hours a day + weight train.
I'm very aware that eating has a significant pyschological component, but, again, if you're going to say "ex-atheletes are often very overweight," I'd like to see studies.