If you are naturally thin....then that's probably a healthy way to be. They say thin people live longer. But, if you are anorexic and just won't eat, then that is deadly because you starve your muscles and they start to feed on themselves. Your organs are muscles too and they eat on themselves....like the heart. One common cause of death for anorexics is heart failure.....it just quits working. Don't know if you're young or not, but as you age, you'll probably gain weight and may even have a weight problem eventually. I was thin as a young person and as I aged, gained weight. Now I'm 63 and overweight.
It affects your overall well-being in EVERY way imaginable. Your mental, physical, physiological, emotional and spiritual balance in your everyday life. It is ideal that you roll around a healthy balance wherein you get enough energy to sustain your growing body to perform optimally through good diet, exercise and enough rest. And haven't seen you on here in a while Dallie :P
I don't think it matters that much because I'm underweight even though I have a six pack and can do curls with 100 pounds other than if you don't eat as much as everyone else you'll have less energy sometimes like when I barely eat I can't finish a four quarters of a game with out resting