Sex hormone critical to proper body weight.

• Position: Estrogen

Estrogen regulates energy expenditure, appetite, and body weight, while insufficient estrogen receptors in specific parts of the brain may lead to obesity. "Estrogen has a profound effect on metabolism," declares internist Deborah Clegg, senior author of a study published in Cell Metabolism. "We hadn't previously thought of sex hormones as being critical regulators of food intake and body weight."

The study is the first to show that estrogen, acting through two hypothalamic neural centers in the brain, keeps female body weight in check by regulating hunger and energy expenditure. Females lacking estrogen receptor alpha--a molecule that sends estrogen signals to neurons--in those parts of the brain become obese and develop related diseases, such as diabetes and heart disease.

Similar results were not seen in males, although researchers suspect other unknown estrogen receptor sites in the brain play a similar role in regulating metabolism for males as well. Estrogen receptors are located throughout the body, but researchers found two specific populations of estrogen receptors that appear to regulate energy balance for females.

The findings are potentially important for millions of postmenopausal women, many of whom have decided...