We’ve all experienced it at some point in our lives: we gather around the table for a nice Thanksgiving meal, then go watch football or catch up with friends and family in the other room, and next thing we know, we’re falling asleep all over ourselves.

Why does this happen every Thanksgiving?!

Is it the boring conversation with Uncle Joe, or is it the turkey and 16 sides you devoured in 8 minutes flat? It could be both, but it may also be neither.

Many people blame tryptophan in turkey for causing sleepiness after a Thanksgiving meal, but what exactly is tryptophan? Tryptophan is a plant-derived, essential amino acid that we all need for normal growth and development, and studies have shown that tryptophan can help mitigate health issues such as cardiovascular disease, chronic kidney disease, cognitive impairment and decline, diabetes, and depression and anxiety. Tryptophan is also needed for the biosynthesis of proteins and, after consumption, produces by-products such as vitamin B6, serotonin, and melatonin.

Serotonin is a neurotransmitter in the body whose function is quite complex, but in a nutshell, it modulates mood, cognition, reward, learning, memory, and vasoconstriction, or closing of the blood vessels and decreasing blood flow. Melatonin on the other hand is a hormone that your brain produces in response to darkness. It helps with sleep, and with the timing of your circadian rhythms (24-hour internal clock). So, if tryptophan produces both serotonin and melatonin to put you in a good mood, decrease blood flow in the body, and promote sleep, then the tryptophan in turkey MUST be making you tired, right? Well, maybe.

Certain types of foods, and the timing of a meal, can make you feel drowsy after you are finished. This decrease in energy after eating is called postprandial somnolence and foods that are dense in protein and carbohydrates are more likely to lead to drowsiness. There are many protein-rich foods that contain tryptophan (see chart below), and carbohydrates help the body absorb tryptophan. So, eating turkey with stuffing, mashed potatoes, sweet potatoes, etc. will probably have your body absorbing quite a bit of tryptophan – and therefore producing a decent amount of serotonin and melatonin.

However, regardless of any food intake, many people experience a drop in energy and alertness between the hours of 3-5 PM due to their circadian rhythms. Many people do not meet their sleep quota on a nightly basis, which is largely why these dips in circadian rhythm in the mid-afternoon occur. According to a 2018 survey, families usually eat their Thanksgiving meals anywhere between 1-3 PM, so with this timing, it makes sense as to why people may feel sleepy after eating. Also, eating large meals, and eating in general, causes blood sugar to rise, and a drop in energy will typically follow. Add alcohol to the mix, especially during the daytime, and that can amplify the drowsiness.

Again, there are many foods that contain high levels of tryptophan, not just turkey. Here is a chart derived from the USDA Food Data Central Repository to give you an idea of some foods that are comparatively high in tryptophan:

And for vegetarian and vegan options:

So, does the tryptophan in turkey really make us drowsy after Thanksgiving? Based on the fact that on non-Thanksgiving days, we eat many foods that contain similar amounts of the amino acid, but don’t get the same drowsy effect, we think it is less about the tryptophan and more likely related to other factors. Specifically, it’s a mix of the time of day you eat, the amount of food you eat, the combination of food you eat, whether alcohol is involved, and whether the game or conversation is compelling or not.

Beacon Physical Therapy

Beacon Physical Therapy would like to wish all of our patients, friends, family, and colleagues a safe and pleasant Thanksgiving holiday!