An occasional midnight fridge foray isn't going to ruin a healthful diet or pile on pounds. But routine and heavy nighttime snacking can be a sign you're eating for reasons other than hunger and the calories can add up fast.

More serious symptoms can point to a little-known eating disorder called night-eating syndrome.

Those who skip breakfast, eat more than half the day's calories after dinner and sometimes wake up and snack likely have this condition. It's characterized by hormonal imbalances that lead to disturbed patterns of sleep and eating.

"Probably one in 10 patients I see who are obese have this syndrome," says bariatric doctor Eve Olson of Carmel, Ind. "A lot of people go all day without eating. The moment they're done for the day, they start in."

Whether you have this disorder or just overeat at night, results can be similar: weight gain and unhealthful eating and sleeping patterns.

Not everyone with night-eating syndrome is overweight, though some research has found that up to 28 percent of obese people have it.

Most people who overeat only at night do so because of habitual food needs, such as pairing eating with watching TV, says nutritionist Nicole Haywood. Or, she says, they're downing food as an emotional response to stress, boredom or loneliness.

"There's nothing inherently wrong with eating late at night." But Haywood says it makes more sense to eat most calories earlier in the day, because that's when people are most active.

While a few studies have found that fat doesn't metabolize as well when you eat late, Haywood says evidence isn't conclusive.

It has been proved that skipping meals, which night eaters often do, leads to overeating. "Fruits and vegetables don't sound so good if you are ready to eat your right arm," she says.

Many people with night-eating syndrome aren't just feeding a bad habit.

Research led by Dr. Grethe Stoa Birketvedt of Norway and American scientist Albert J. Stunkard of the University of Pennsylvania, has found evidence that three hormones play a major role in causing the disorder, which sometimes can be hereditary. A specific gene hasn't been found yet.

In those with the syndrome, levels of melatonin — the sleep hormone — are significantly reduced. Leptin, an appetite suppressant, doesn't rise to normal levels in night-eaters, suggesting hunger may awaken them. Lastly, cortisol, the "stress hormone" that rises when you're tense, is higher in night-eaters, maybe leading to wakefulness and eating.

Typically, people with the syndrome wake up one to three times at night and eat small, high-carbohydrate snacks, says Birketvedt, medical director of the Norwegian Nation's Obesity Program at Aker University Hospital in Norway. She also has done research at the University of Pennsylvania and Mount Sinai School of Medicine in New York.

Unlike other nocturnal eating disorders, in which sufferers are asleep, Birketvedt says people with this syndrome are awake. Stress or an emotional event can trigger the disorder, which can come and go at any time in a person's life, she says.

While doctors are still studying its exact cause and treatment, some treatment methods do work.

Taking melatonin before bedtime helps some sleep better. So does eating foods rich in the amino acid tryptophan, including turkey, chocolate milk and salmon, said Birketvedt.

Research at the University of Pennsylvania has found the antidepressant Zoloft helped, along with therapy to change eating and exercise patterns. But Birketvedt warns that these are only short-term remedies.

Night eaters can take other steps — finding nonfood stress relievers and eating small, regular meals during the day — that may curtail night food forays.