"It is likely that the physiological mechanism responsible for weight gain is 'built in' to the act of singing," Osin said.

Osin said that those singers who don't gain a lot of weight may not be as susceptible to the hormone, or may be working much harder to keep the weight off. He cited singers' nomadic lifestyles—solitude, hotel meals, restaurants—as another factor in their weight gain.

Opera singers are facing increasing pressure to stay as slim as other performers. Soprano Deborah Voigt lost 100 pounds after gastric bypass surgery in 2004. Although she had recently been fired from a Royal Opera production of Ariadne auf Naxos because she would not fit into a slinky dress, Voigt said in interviews that she had been concerned about her health for some time, and had already decided to undergo the procedure.