Most of us have indulged in a snack by the light of the fridge late at night. Those who do it too excessively and too compulsively, however, may have an eating disorder called night eating syndrome.

Colleen Rand, of the University of Florida at Gainesville, says that those afflicted may consume half or more of their daily calories after seven at night. Because they feel guilty (or simply aren't hungry), night eaters may also experience "morning anorexia," abstaining from eating the next day. Night eaters are also frequently troubled by insomnia, which Rand believes might be caused by the same tension and anxiety that drives their overeating.

A study Rand and her colleagues conducted revealed that, among patients so obese that they had to have surgery, 58 percent had experienced night eating syndrome (and 27 percent continued to do so even after surgery). The syndrome's prevalence among the general population was far lower—about 1.5 percent.

Wider recognition of night eating syndrome may lead to more extensive research into the disorder, says Rand. Possible treatments include a program of regular exercise and reestablishing normal daytime eating patterns.