The thinness imposed by the dictates of fashion is dangerous. Some modeling agencies require them to lose weight even if they are at a healthy weight. Leanness due to professional constraints, poor absorption or anorexia can pose a health risk. Leanness is also a risk factor for osteoporosis. It acts on hormones, especially sex, and can disrupt the fertility of young women.
Some messengers do not get to the brain and thus disrupt the appetite. Several natural health factors as well as poor lifestyle habits are involved.
Difficulty absorbing nutrients may be a sign of gluten intolerance in wheat and other grains or other components of foods such as casein in milk. Inflammatory bowel disease or impaired intestinal flora may also be involved.