I have been very fit my whole life, and stayed skinny until I went away to university where I experimented a bit, and ended up gaining a lot of weight whilst still playing sport.
I'm still quite active and play a handful of sports, so I don't really get tired going up stairs or anything. I think it's a pretty good trade-off - I love my new bigger weight but I still am sporty, and people tend to underestimate my capabilities as well which is always funny