Is it really JUST the turkey that makes me sleepy on Thanksgiving?

At my family’s Thanksgiving meal there are three rules.  One - don’t stop eating. Two - take a bite and pretend to like your Aunt’s new favorite vegan dish. Three - mark your territory on the couch for your inevitable post meal coma nap.

Growing up I was always told that the reason why you nap after the meal is the turkey, more specifically the tryptophan in the turkey. This is common talk at the dinner table at Thanksgiving; that tryptophan makes you tired. Is this true? The answer to this question, and many other ones in science, is…….. Yes and no. To understand the complexity to the rather simple question, first we must understand the chemistry of tryptophan.

Tryptophan is an essential amino acid (these are the building blocks of proteins - meaning you put a bunch of them together and you make a protein). There are two groups of amino acids (AA):  non-essential, which your body can make endogenously, and essential, which your body cannot make. These AA’s needs to be consumed through a food source. Tryptophan is unique from the other essential AA’s in that tryptophan can cross into the brain through the blood brain barrier (BBB). Once in the brain, tryptophan can be converted into serotonin, and serotonin can be converted into melatonin. At this point you might be saying “eureka!” because melatonin is the hormone secreted by the pineal gland that regulates wakefulness. So, because tryptophan is basically converted into melatonin, turkey is what makes you tired. However, we cannot just end here because there is more to the story.

While most of us will engorge ourselves with turkey, we will eat a copious amount of other food as well, mostly sweets and starchy side dishes. These yummy, sugary sweets and starches will cause a sharp rise in the hormone insulin. The role of insulin is to take energy (glucose) to the cells. As insulin rises, it will ultimately cause a decrease in your blood sugar. A decrease in blood sugar has been shown to be associated with fatigue due to the fact that you have less glucose in your blood to be delivered for energy to the cells.

The hormonal response to the chemical makeup of the food is a large reason why you feel tired after the meal, but there is another reason as well. The last reason why …..drum roll please…….digestion. After a meal, blood is shunted to the gastrointestinal (GI) track to help breakdown and absorb the meal. Blood being shunted away from our brain to our GI track can also make us sleepy.

What makes you tired after thanksgiving? The answer is a combination of tryptophan, insulin and the overall amount of food. So remember, as with most straight forward scientific questions, the answer is never straight forward.

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