Even though many of us wake up in the middle of the night thirsty and/or needing a bathroom, few of us decide to stay awake to eat another dinner. To be sure, we may munch on a graham cracker, nibble on some leftover pie, or drink a glass of milk with some cookies. But with the exception of a category of people called night eaters, we rarely are hungry enough to eat a full meal, even though it has been hours since we last ate. The almost physical inability to put much food in our stomachs is evident with the lackluster appetite we may approach breakfast served on a transatlantic flight at two or three in the morning. We are awake, more or less, but our stomachs are not. Conversely, some of us can tell time by the mid-day and early evening rumbles in our stomach signaling, “Time to eat!” Why are we hungry for lunch or dinner five or fewer hours since the previous meal, and yet not hungry in the middle of the night, eight or nine hours after we had dinner? By the time we leave infancy, most of us are unlikely to wake up for a 2 A.M. feeding.
A hormone, secreted by the stomach, but acting on the brain, may be the answer. Ghrelin (rhythms with Mary Ellen) seems to initiate eating at certain times over a 24 hour cycle, but not at other times. Although it seems as if we eat by the clock as in, “It is noon so I must be hungry,” this is apparently not the case (At least not in a research situation). About seven years ago, in a study published in the American Journal of Physiology by D.E. Cummings and colleagues, ghrelin levels were measured in volunteers whenever they started eating a meal. The researchers found that when the volunteers were most hungry, right before they started a meal, their ghrelin levels were high. After eating, ghrelin levels in the blood decreased and, as time passed, slowly began to rise again. Five or six hours after the previous meal, hunger and ghrelin levels again were high, and the subjects started on their next meal.
So why are we all not in the kitchen at 1 or 2 A.M. looking for something to eat, 6 or 7 hours after dinner? Most of us are asleep and if awakened would probably turn down a sandwich or some scrambled eggs. We are not hungry. The reason? According to research reported in the European Journal of Endocrinology by Natalucci, et al, the level of the hunger hormone is lowest between midnight and 7 A.M.
But some people do wake up every night hungry enough to eat more than a few crackers and drink some milk. These so-called night eaters may actually consume as many calories as the rest of us eat at dinnertime. They are not eating in order to fall back asleep but because they are hungry. It is unclear if they wake up because they are hungry or notice how hungry they are when they wake up for other reasons such as noise or a need to go to the bathroom. Hungry they are, however, and apparently because night eaters have an abnormally high level of ghrelin in the blood between midnight and morning. It is as if this hormone is out of sync with the other hormones, primarily melatonin, that should be keeping them asleep, not microwaving pizza or defrosting a steak in the middle of the night.
No one quite knows what to do about the high levels of the hunger hormone in the wee hours of the morning. Researchers acknowledge that the rise of gherlin is delayed, so that instead of increasing late in the afternoon/early in the evening, when we normally would be eating our evening meal, it seems to peak five or six hours later. One thought is to expose night eaters to early morning light therapy similar to the light boxes used by people with SAD (Seasonal Affective Disorder). According to a paper by Goel N. Stunkard and others in the Journal of Biological Rhythms, night eaters who have been exposed to early morning light respond by eating at normal meal times and will decrease their nightly food consumption. Maybe the light changes the rhythm of ghrelin release so that it approximates the normal sleep/wake cycle. Or perhaps waking people up early to sit in front of a light box gets them to eat breakfast early in the morning (although it is hard to believe they will be hungry) and this sets up a normal ghrelin prior to lunch and then dinner time.
Or perhaps the answer is to move to Spain where everyone seems to eat supper after the late show.