Time for Word of the Day Wednesday. Well, it’s a phrase today, and one of my favorites: POSTPRANDIAL SOMNOLENCE. It’s the itis. The food coma. That sleepy, lethargic feeling as you undo your belt buckle a few notches after feasting on Thanksgiving dinner. Oh, by the way – happy belated Turkey Day!
So, why does postprandial somnolence happen? Well, for one, after we’ve eaten, the body recognizes there is food in our digestive system, so our parasympathetic nervous system kicks on. It slows our heart rate and increases intestinal activity and blood flow to the muscles in the GI tract. It’s the “rest & digest” system (versus the “flight or flight” sympathetic nervous system you may have heard of).
But, my dears, we need to correct a few misconceptions: (1) no, you’re not sleepy because your brain has shunted all your blood to your digestive system. It’s diverted from your skeletal muscles. Oxygen and blood flow to the brain is really, really tightly regulated because it’s so darn important, and it doesn’t change much after a meal. So there’s that.
Secondly (2), the tryptophan in turkey isn’t what makes you sleepy after Thanksgiving feasting. Tryptophan is an amino acid that is in most protein-rich foods. Per the USDA Nutrient Database (2007), the tryptophan in turkey isn’t any higher than that in beef, chicken or other meat, and turkey doesn’t make your blood levels of trypto’ spike. But eating turkey along WITH high carbohydrate foods (stuffing, mashed potatoes, etc) actually COULD cause the sleepiness. Why? Carb-rich food increases your production of insulin, which stimulates some (other) amino acids to get absorbed from the bloodstream – but *not* tryptophan. Since your blood levels of trypto’ will be higher, it’ll be absorbed in higher quantities across the blood-brain barrier and into your cerebrospinal fluid (CSF). CSF converts tryptophan into serotonin, which is then turned into melatonin by your pineal gland. If I’ve lost you by now, don’t panic! Here’s the point: melatonin is a hormone that regulates our sleepiness. More melatonin = more sleepy. More carbs with your protein = more sleepy.
So really, it’s the carb+turkey combo to blame, not just the turkey. Well, the combo, and probably your ol’ Uncle Bob droning away about his favorite football team.
BONUS FUN FACT if you’ve read this far: taking melatonin (it comes in OTC pill form!) both before and after a surgical procedure was found to reduce pre- and post-operative anxiety in adults (Hansen et al 2015). I guess another takeaway here could be that if you’re visiting some stress-inducing relatives, maybe it’s worth considering some melatonin (or an extra helping or two of food) next Thanksgiving! Happy belated POSTPRANDIAL SOMNOLENCE DAY! ???