An acquaintance of mine is spindly, and given her present line of work would be modeling were she taller than five foot four. She has a few congenital weaknesses, however, including poor circulation; and I do believe she was at one time accused of depriving herself, so to speak.
Could be true, but environment probably does play a big part too?
Women on one side of my family are tiny. I'm probably shorter than everyone else here *lol*. Have always been petite, though the figure is there (think hourglass, though a pocket-sized hourglass). . Some guys do tell me I'm too thin. But they're surprised at how much I eat (pfft. go figure). .
Have never dieted, eat regular meals and love food. But have been the same weight for the last 10 years give or take a few pounds. Did try to put on more weight, but once I fell sick/got stressed, it'd drop off to the norm. . .
Apart from that, no ill-health though. . Exercise. . I dance about 3 - 5 hours a week, sometimes up to 10 depending on how moody/in need of release I am, but that's about it. . .