This is very true. When it comes to eating, I am not healthy at all, but I'm still a very toned 180 lbs (I am 6'2'') and I never seem to gain any weight no matter what I eat due to my fast metabolism. Although I usually only eat twice a day so maybe that has something to do with it, but I've always been skinny/tone my whole life, and I don't work out nearly as often as I should.
I'd love to get into a strict workout at least 3-4 times a week of heavy lifting, and start eating a lot more (and healthier) and see where that takes me