Haven't been weighed in a while, so I don't know if I'm 'underweight', but I'm the skinny nerd type, not the fat nerd type.
Resultant of eating better, cutting soda and other crap out of my diet before it even becomes a problem. Most days I'm on one meal and that's rice, vegetables, fish etc from the dining hall on campus. Hell, due to the meat sucking I'm almost vegetarian if it weren't for the fish and approximately one bacon cheeseburger per fortnight.
There's not much need for energy reserves when my entire exercise regimen consists of sprints to class.