The Perils of the Midnight Muncher: Night-Eating Syndrome

By Dr. Caroline Cederquist

Do you know one of those people who never seems to eat -- no breakfast, no lunch, little snacking throughout the day? Maybe you are one of these people who's always declining the lunch invitation, and all day long, you're never really hungry, or not so hungry that you feel you need to respond to it.

But perhaps over the years, you have nevertheless accumulated excess weight, maybe even quite a lot of it. And it may be as much a mystery to you as to others, who wonder quietly, "How is that happening? I never see him eat."

And you might wonder yourself, "I eat nothing all day long, so where are all these calories coming from?"

Calories Lurking in the Night
As is true for most of us, the calories are coming from the kitchen. But for folks with an odd disorder called Night-Eating Syndrome (NES), those calories sing an especially alluring song after the sun goes down. Most people have the experience of the occasional midnight snack, but if you find yourself with your head in the fridge night after sleepless night, and fretting as your weight increases in spite of your meager food intake all day, you may be a victim of NES.

First described in the medical literature back in 1955, NES is characterized by three main features: a lack of appetite in the morning, overeating in the evening, and insomnia at night. NES is not particularly rare. While the prevalence of NES in the general population is estimated at about 1.5 percent, it's far more common among overweight folks. One study reported 8.9 percent of patients in a weight-reduction clinic and 12 percent of overweight patients visiting a nutrition clinic were diagnosed with NES. And 26.5 percent of the subjects classified as severely overweight were diagnosed with NES.

Although not everyone with NES is overweight, a study comparing normal-weight and overweight night eaters against control subjects found that the main difference between the overweight and normal- weight NES subjects was age. The overweight night eaters had simply been at it longer, and investigators found that more than half of the older NES patients specifically recalled that their night-eating preceded their weight gain.

Interestingly, the chief difference between the normal-weight night eaters and the study's control subjects with normal eating patterns was that the NES group consumed more calories overall in any 24- hour period.

This is consistent with other studies of breakfast skippers, who say they don't feel hungry in the morning, and often convince themselves that with breakfast behind them, that's one meal's worth of calories they have escaped for the day. On the contrary, study after study has shown that people who skip breakfast have higher caloric intake overall in any given 24-hour hour period. The "skipped" calories just show up at some point later in the day, and then they bring their friends! It seems that it works pretty much the same with night eaters.

Behavioral and Chemical Markers of NES
What distinguishes the night eaters from other daytime meal skippers is that the primary hallmark of NES is insomnia -- not just difficulty falling asleep, but frequent awakenings during the night. Like many people with depression, most night eaters can trace the beginnings of their insomnia problems to a period of elevated stress, such as a job loss, relationship break-up, or any of the many other curve balls life slings at us. But NES patients report that their mood is lower in the night and early morning, and that differs from people diagnosed with simple depression.

NES sufferers also report that they feel driven to snack during these nighttime wakeful periods, and that their nocturnal fridge-foraging expeditions are particularly focused on high-carbohydrate foods. Peanut butter and jelly sandwiches feature prominently among the prey of nighttime snack hunters.

So armed with these life-history reports from night eaters themselves, investigators set out to identify physiological and biochemical measures that might distinguish night eaters from the general population.

They were not surprised to find that NES sufferers had significantly lower levels of melatonin, a hormone produced by the brain's pineal gland, and intimately involved in the control of sleep-wake cycles. The levels of melatonin decline with increasing age, and this is consistent with the increased incidence of sleep and weight problems in general among the middle-aged to elderly.

Midnight munchers also had lower levels of circulating leptin, a hormone that has a central role in fat metabolism, and their cortisol levels were higher. Cortisol is the major natural glucocorticoid in humans, our primary stress-response hormone. This finding surprised neither the patients or the investigators, because so many of the night eaters reported that their moonlight foraging expeditions began during periods of elevated stress.

Still, a lot of us have stressful periods in life, and we don't become nocturnal eaters. But in NES sufferers, their internal clock seems to have gone out of whack.

Our circadian rhythms are the patterns of daily activities and functions that are influenced by the changes in light and dark, temperature, etc., over the course of a 24-hour day. What appears to happen in NES is that the circadian pattern of sleep stays normal (nighttime), but that the circadian pattern of appetite becomes out of phase by six hours or so, resulting in its overlap on the sleep cycle. It isn't understood exactly how this happens initially, but scientists can reproduce this phenomenon in experimental animals.

Sometimes our bodies are smarter than we think. The finding that night eaters have a strong preference for high-carbohydrate snacks -- yes, even more than the usual high-carb American diet, with a 7:1 carbohydrate-to-protein ratio among NES sufferers -- led several investigators to suggest that the high-carb snacks may be the body's attempt to increase the levels of tryptophan, an amino acid essential to both sleep and mood. So that peanut butter and jelly sandwich may be an attempt at self-medication.

Treating NES >