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Decoding the Food Coma

As we exit from the comfortable monotony of the Thanksgiving weekend, let’s look back on Thanksgiving and forward to the approaching Christmas holiday at what really brings us all together — the food, or more accurately, the shameless gluttony. Everyday nonsense is put aside, people shut up, and one is happy to just listen to the smacking of greasy lips. And once we’ve shoveled into our mouths all that our bodies can tolerate, we are overcome by the effects of a condition that has many names. Some call it food coma, others The Itis, but whatever you call it, we all know that feeling of heaviness and fatigue that exists after a large meal. We find ourselves slouching in our chairs and loosening our belts while our bodies desperately work to digest the inhuman load of matter that has settled in our stomachs. It is familiar to all, though the specific cause of it isn’t exactly known.

Science calls it postprandial somnolence, and there have been a variety of myths about it that have subsisted, most of which are inaccurate. Some blame the chemical tryptophan found in turkey for the drowsiness associated with post Thanksgiving meal satiety. Tryptophan is a precursor to the neurotransmitter serotonin, which regulates mood and which in turn converts into melatonin, a neurohormone which helps regulate our sleep cycles. The logic is that turkey is loaded with tryptophan and since we’re loaded on turkey, we’re bound to get a bit euphoric from the serotonin and then super drowsy from the amount of melatonin that will overtake our system. However, tryptophan is present in all poultry as well as some red meats and not at a higher concentration in turkey. Also, turkey isn’t the only thing that we consume on Thanksgiving. A feast is defined by both the bounty of food as well as the wealth of variety, so turkey can’t be the sole culprit of the food coma.

Another myth about the food coma is that it is caused by the redistribution of blood flow from cerebral to mesenteric (abdominal) vessels. Researchers attempt to debunk this in the article, Debunking the myth: neurohormonal and vagal modulation of sleep centers, not redistribution of blood flow, may account for postprandial somnolence. According to the myth, reduced blood flow in the brain could cause a lack of oxygen in the brain, making one feel tired.  But as the article states, this essentially goes against the fundamental principle of neurovascular physiology, which is that across a range of conditions, the body makes sure blood flow in the brain is maintained, especially during strenuous activity and exercise. So why would a heavy meal change this if a jogging session on the treadmill doesn’t?

One alternative hypothesis researchers introduce brings melatonin back into the picture, but not through intake of tryptophan. They implicate the activities of gut hormones as a possible cause for drowsy effects of a large meal. Recently discovered gut-brain hormones like Orexin, which promotes hunger and alertness, are inhibited after feeding. In turn, melatonin production rises quite a bit after meals. As I’ve mentioned earlier, melatonin is involved in our sleep-wake cycle and certain studies have shown that melatonin administered into the hypothalamus of animals as well as humans can induce sleep. Debate continues on this subject and it goes to show that the body still holds many mysteries, even of something as seemingly simple as a food coma.

Not only are we not sure as to exactly how it happens to us, but the question also remains as to why it happens. One possible adaptive function explored by the articles is that digestion, as metabolically taxing, may require focused energy expenditure so that in one’s passive state, an individual can conserve energy for other activities like the pursuit of more food in the future. Generally though, the food coma is just something we accept and don’t put much thought into. So the next time you are treated to a big meal and find your eyes getting heavy afterwards, ask yourself why. Someone’s bound to figure it out eventually.