"It's counterintuitive that an emaciated young woman with almost no subcutaneous (below the skin) fat would be storing fat in her marrow," lead researcher Dr Catherine Gordon, an endocrinologist and director of the Bone Health Program at Children's Hospital Boston, is reported to have said.

Anorexics beware!

Anorexia nervosa, which affects mainly young women, leads to extremely low body weight and an obsessive fear of weight gain. People with anorexia nervosa also have other psychological difficulties and mental illness. Clinical depression, obsessive compulsive disorder, substance abuse and one or more personality disorders may be the most likely conditions to be comorbid with anorexia. High-levels of anxiety and depression are likely to be present regardless of whether they fulfill diagnostic criteria for a specific syndrome.

The study

For the research, MRI scans were taken of the knees of 40 girls, who averaged 16 years old -- 20 with anorexia and 20 who were healthy. The girls with anorexia had higher fat content and less than half as much healthy red marrow in their knees, the researchers found. The difference was also seen in the lower thighbone and upper shinbone.

Fatty bones

Earlier studies had found that hormonal changes in malnourished people trigger the bone marrow's mesenchymal stem cells to turn into fat cells rather than bone-forming cells. That could explain why people with anorexia lose bone mass and sometimes develop osteoporosis, the researchers said.

"Bone formation is very low in girls with anorexia, and that's a particular problem because they are growing adolescents who should be maximally forming bones," Gordon said. "But because of the hormonal alterations induced by malnutrition, the bone marrow stops yielding the needed cells to form bone. Instead, the stem cells are pushed toward fat formation."

Gordon plans further studies to find out why this occurs. One theory is that it's due to the body's attempt to store energy and preserve warmth. Because of their lack of insulating fat, people with anorexia often develop extremely low body temperatures (hypothermia) and need to be hospitalised.

Pic: Peter W