SmartyShorts said:
No no no, when life gives you lemons, you take pictures of Spiderman. Also thank you again.
Alright, you lost me there....
Don't get me wrong, Spiderman is awesome (though I'd argue for Batman any day, the only man capable of wearing his underwear on the outside and still be dark and gritty) but what's he have to do with lemons?
And to keep this at least slightly on topic:
I'm personally quite lucky to have an insanely fast metabolism. I've got below 5% body fat and no matter what I do I can't get any more and I don't know if it's related but I'm quite incapable of getting hangovers, any alcohol I drink leaves my system before I wake up so besides have to visit the toilet several times I don't notice a thing

, of course I hardly ever drink so it's kinda irrelevant[footnote]Anything not related to elephants is irrelephant (sorry, hearing Cave Johnson causes me to spout bad jokes)[/footnote].
Only downside I noticed of my metabolism that that when I tried my hand at semi-professional rowing (training every day for 2-3 hours, no alcohol, 8+ hours of sleep every night etc.) my body simply wasn't able to keep up and I had to eat an extra full plate of carbohydrates at every meal (usually plain rice with ketchup) until I felt like puking. In the end it wasn't even enough and I developed a rather serious case of overtraining [http://en.wikipedia.org/wiki/Overtraining] forcing me to give up sporting at that level.
It's not really comparable to some of the more serious conditions out there but it did give me an inkling of understanding on how effing horrible dieting can be.
But overtraining is another 'condition' that can cause serious weight gain. While you're sporting at a high level your body demands extreme amounts of nutrition, and if you're stopping you have to do so slowly. A little less each week so your body can adapt to it's new nutritional demands. But when you get seriously overtrained your body becomes quite literally incapable of sporting (you sleep 14+ hours per day whether you want or not, experience extreme nausea and even fainting when you do exercise etc. at least that's what I experienced) and there's no way for you to gradually build it down. Your body keeps on demanding your previous levels of nutrition and working as if you're doing heavy exercise daily but there's no way you can actually do the exercise required to burn it all so it all just gets stored and in a very short amount of time you can grow very fat.
I luckily didn't experience that, was way too exhausted and nauseous at the time to eat regularly, but there's quite a few ex-top athletes who are now seriously overweight. Either due to this or related causes.