WE'VE all been there at some point in our lives: raiding the fridge or cereal cupboard in the wee small hours. In childhood, a midnight feast was the holy grail of mischief; who could eat the most under the dramatic veil of darkness without being caught. The thrill lay in being awake at some unearthly hour, scoffing food you weren't supposed to and subsequently disposing of the evidence. Appetite or hunger were never the issues; having fun and getting away with it were the only considerations.

But that was then. Should you behave like this as an adult - and we're not talking about a one-off, naughty midnight feast with your other half, but regular, unaccompanied nocturnal suppers throughout the week - then you may be suffering from something a little more serious than lack of self control.

There is nothing wrong with the occasional snack should your stomach wake you up earlier than usual. But according to medical experts, if your sleeping patterns are regularly punctuated with trips to the larder, then you may be suffering from a type of sleep, eating and mood disorder.

Doctors in America have identified two main types of disordered eating at night, although neither is formally known as an eating disorder in the way we understand anorexia nervosa or bulimia nervosa to be.

Nevertheless, night eating syndrome and nocturnal sleep-related eating disorder, also known as NSRED, are growing problems in developed countries. This can be seen in the year on year rise in obesity. Experts at the Centre forWeight and Eating Disorders at Pennsylvania University say they see more obese people with the syndromes than any other group. Night eaters can consume anything between 500 calories and half their daily recommended energy intake in a couple of trips to the kitchen. Foods of choice among night eaters tend to be high-carbohydrate and high-sugar foods, such as cereals, crisps and biscuits.

Yet because it is a newly recognised condition the number of sufferers is hard to estimate, although Dr Albert Stunkard, professor of psychiatry at the University of Pennsylvania, the world's leading authority on night eating, has said that 1.5 percent of the general population may suffer from the syndrome.

Stunkard, who first spotted the symptoms of the condition in 1955, also says that should night eating remain untreated individuals can develop various physical and mental health problems.

Dr Kelly Allison, a colleague of Stunkard's at Pennsylvania, is studying the causes, prevalence and treatment of night eating syndrome and NS-RED. "Eating during the night can be a very hard cycle to break, " she says. "It can lead to daytime sleepiness and feelings of guilt. It is unclear how direct the relationship is between night eating and weight gain, but it certainly seems to hinder weight loss efforts. The compulsive nature of it is often very distressing for those who suffer from it."

According to Allison, the underlying causes of night-eating disorder are still to be identified and treatment plans are in development. It is thought that a combination of biological, genetic and emotional factors may contribute. One theory is that people with the condition are under stress, either recognised or hidden. Their bodies are flooded with cortisol, a stress hormone. Eating may be the body's attempt to neutralise cortisol or slow down its production. Certainly, stress-reduction programmes appear to help.

Although it concerns the same effect - overeating at night - NSRED is quite different from night eating syndrome. With NS-RED, individuals eat while seeming to be sound asleep. They may eat in bed or roam through the house and prowl the kitchen. They are not conscious during such episodes, and when they awake they either can't remember or have only fragmented memories of having been awake and eating. Doctors say that NS-RED occurs in a state somewhere between wakefulness and sleep and may be related to sleep-walking.

Again, similar to night eating syndrome, those with NS-RED consume foods that tend to be high-carbohydrate, high-fat, high-sugar "comfort" foods that they deny themselves while awake. That said, anecdotal examples of bizarre combinations of food have been recorded in NS-RED cases such as hotdogs dipped in peanut butter, raw bacon smeared with mayonnaise or even non-food items such as soap sliced like cheese.

Allison says experts believe night eating is not merely a habit but a clinical illness marked by changes in hormone levels. As individuals become more anxious and depressed at night, their eating increases. It is thought sufferers eat to help themselves sleep by boosting levels of serotonin, a chemical involved in the brain's messaging system. "In other words they are medicating themselves, as eating high-carbohydrate food increases serotonin levels, which stimulates sleep, " says Allison. "I think stress triggers it but you have to have a specific kind of make-up to respond in this way, and I think that's genetic."