Previous studies have noted that some bulimia nervosa patients have low levels of a hormone called leptin in their blood, while others have normal levels. Researchers from Italy suspect this hormone disparity may relate to the severity of the disease.
Leptin is thought to influence body weight through its action on the hypothalamus, the brain portion that helps regulate appetite and satiety.
"While anorexic patients tend to have low plasma leptin concentrations, bulimics often exhibit levels ranging from anorexic-like values to normal concentrations," says lead study author Palmiero Monteleone, M.D., from the Department of Psychiatry at the University of Naples SUN in Naples, Italy. "The reasons for such diversity have not been explained."
To attempt to explain this disparity, Monteleone and colleagues measured leptin blood levels of 127 women divided into three groups. One group consisted of anorexia nervosa patients, another group of bulimia patients, and a third group consisted of healthy volunteers.
As with other studies, the anorexia patients had low leptin levels compared with the healthy women, while the bulimia group was divided: Approximately half had normal leptin levels and half had levels comparable with the anorexia patients. The researchers performed more analyses to glean clues as to why the leptin levels among the bulimics weren't uniform.
The low-leptin bulimia patients had suffered from bulimia for a significantly longer period and they engaged in more bingeing and vomiting compared with the normal-leptin bulimics, the researchers found. They also found a higher number of patients with borderline personality disorder in the low-leptin group of bulimics.
The study findings are published in the November/December issue of the journal Psychosomatic Medicine.
"Our study findings show that leptin production is decreased in the subgroup of bulimic patients with a more chronic disease and with a greater severity of the bingeing and vomiting behavior," says Monteleone.
It is known that when body fat and weight drop past a certain point, leptin blood levels drop, stimulating appetite. But these study findings suggest that factors other than body weight changes -- such as the chronic malnutrition and bingeing behavior -- may also impair leptin secretion. The bulimics in the low-leptin group had similar body weight to the normal-leptin bulimics.
Bulimia patients generally exhibit normal body weight but their eating habits are far from normal. They take in large amounts of calories during binges but regurgitate most of them by vomiting. They also often choose unhealthy foods during binges and may suffer from chronic nutrient deficiencies, according to the study. Also, a previous study found that binge eating in healthy individuals affected the normal production cycle of leptin.
"It seems possible that in the bulimic patients with low leptin levels, the chronic malnutrition acts in concert with the bingeing behavior to profoundly and persistently affect leptin synthesis," says Monteleone.
Regarding the finding that the low-leptin bulimic group exhibited higher levels of borderline personality disorder, Monteleone notes "this difference is not easily understandable in terms of leptin secretion."
The researchers pointed out several limitations to the study, including that they based their findings on only one blood measurement. They also suggested longer-term studies should address whether bulimics with infrequent bingeing and vomiting will develop lower leptin levels over time.
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