“You can tell you ate too much for Thanksgiving when you have to let your bathrobe out.” – Jay Leno

So, why did you get so sleepy after that big Thanksgiving dinner the other night?  Sure, you had been looking forward to that feast for weeks.  Turkey, mashed potatoes, cranberry sauce, pumpkin pie, and all the rest of the bountiful meal.  Does it get any better?  But after that second, or maybe third, helping you are ready for a nap……What most people these days call the post-Thanksgiving dinner ‘crash’.  Often the blame falls on that oh so awesome bird, the turkey, because it is packed with the amino acid tryptophan.

When we eat foods that contain tryptophan it travels in the blood from our digestive system through the blood stream and later enters the brain.  One of the functions of tryptophan is to act as a chemical precursor to the creation of serotonin, a widely found neural chemical in the brain.  Serotonin calms us down and helps us have pleasant thoughts. And, it can be converted to melatonin which is a hormone that has many functions.  One such function is to control our sleep-wake cycles, thereby creating sleepiness.

But, the “bird” does not get all the blame.  Not by a long shot.  Scientists now know that tryptophan can really only make a person tired right away if it is eaten or taken on an empty stomach by itself without any other amino acids.  Taken in isolation tryptophan would increase brain serotonin, but no food source contains tryptophan in the absence of other amino acids.  There is a lot of protein in a serving of turkey and it is likely not the only food on the table.  And, the amount of tryptophan eaten during a holiday meal is generally too small to have any significant effect.

Experts now believe that the sleepiness may in large part come from the high carbohydrate intake that often comes along in the “rest” of the Thanksgiving dinner, and ironically one of the leading culprits may actually be the dessert.   Eating carbohydrates increases brain serotonin despite the fact there is no tryptophan in carbohydrates.

Simple carbohydrates are in many of the things consumed at the Thanksgiving meal, like white flour used in gravy, stuffing, white potatoes, sugar in sodas, corn syrup and marshmallows added to sweet potato dishes, and desserts.  These are rapidly metabolized into sugars that can make our blood sugar levels temporarily spike very high.  Our body quickly recognizes that the blood sugar level is moving up too fast and starts sending out insulin to reduce the blood sugars.  With a rapid and significant spike in blood glucose the body often misjudges how much insulin will be needed and releases too much. This can shift us into a rapid drop in blood glucose to a state of low blood sugar (hypoglycemia) and when that happens we tend to start nodding off.

Another offender is fats.  Fats slow down the digestive system, giving Thanksgiving dinner plenty of time to take effect.  Fats also take considerable energy to digest, so the body will redirect blood to your digestive system to meet its digestive needs.  When you have diminished blood flow to the rest of the body (especially the brain) as a result of eating meals rich in fats, you also tend to feel lethargic.

And, let us not forget the ‘celebratory’ beverages (beer, wine and other alcoholic drinks) common to this time of year feasts.  All have a notable calming effect.

Finally, there is the potentially relaxing environment around the dinner table.  Although for many the holidays are stressful, the meal is often the most relaxing part of the holiday festivities.  The dinner feast provides the opportunity to relax, kick back, and enjoy the wondrous bounty of our lives.

So, why did you get so sleepy after that big feast the other night?  You cannot just blame the turkey for that well anticipated postprandial torpor.  It is a combination of the type of food, amount of food, and festive environment…….Here is hoping you had a very Happy Thanksgiving, and wishing for you a healthy mind and healthy future.