I was 6'1 and 120 at my lowest. Wasn't experiencing any health problems, I was just lazy about eating and was on my feet 10-12 hours a day. Also smoking maybe 3 packs a month at the time which didn't help, but before smoking the most I'd ever weighed was 135. I was a really picky eater as a kid and just didn't like most food. Started eating more, working out, and quit smoking to get my weight up just because I was tired of being so skinny and weak, but not because of health issues.