A Hormone That May Suppress Appetite and Bone Formation in AN

When patients with anorexia nervosa (AN) severely restrict food intake, severe undernutrition often develops. While the specific factors that control food intake in this population are still unknown, intake may be affected by suppression of hypothalamic appetite signals from the brain or by more complex interactions. Hormonal appetite regulators include anorexigenic peptides such as peptide YY (PYY). PYY arises from the intestines and acts via the Y2 receptor. Animal studies have shown that the Y2 receptor may regulate bone formation.

A study of teens with anorexia nervosa

Results of a recent study of 23 patients with AN and 21 healthy adolescents 12 to 18 years of age have highlighted the possible actions of PYY in AN (J Clin Endocrinol & Metab 2005; 10:1878). Anne Klibanski, MD, and colleagues at Massachusetts General Hospital and Harvard Medical School hypothesized that PYY may be elevated in AN and may contribute to decreased food intake and decreased bone formation.

The adolescent girls with AN and healthy control subjects were admitted for an overnight stay at Massachusetts General Hospital. Their height and weight were measured and all had frequent sampling for growth hormone (GH), leptin and ghrelin overnight. Fasting blood samples were obtained for PYY, glucose, insulin, IGF-1, total triiodothyronine (T3), and estradiol.

Bone age was established with an x-ray of the left wrist and hand. Bone age and body composition were measured by dual energy x-ray absorptiometry (DXA). In addition, three serum markers of bone formation were measured, including osteocalcin, carboxyterminal propeptide of type 1 collagen, and bone-specific alkaline phosphatase and two urinary markers of bone resorption.

The girls kept food diaries for three weekdays and one weekend day. Subjects with AN were followed for one year and examined again at weight recovery—defined as a 10% increase in body mass index (BMI, or kg/m2). PYY levels were available for 10 girls with AN.

Results: patients had higher PYY levels

PYY levels were significantly higher in girls with AN than in controls. Weight recovery (defined as a 10% increase in BMI) in 10 girls with AN was associated with a trend toward decreased PYY levels. Levels of PYY were predicted by nutritional markers including BMI and fat mass and by resting energy expenditure (REE). Gonadal hormone levels and total T3 levels also predicted PYY levels. At this stage in the research, it is difficult to know which came first–whether AN and starvation caused the elevation of PYY levels or if the disease was affected by the PYY levels.

According to the authors, decreased food intake in patients with AN may be a result of anorexigenic effects of high levels of PYY. The authors also found that PYY was an important predictor of most bone turnover markers. Thus, high levels of PYY were associated with low levels of these markers, suggesting that PYY may also affect bone metabolism.