Why Does Thanksgiving Dinner Make Some People Sleepy?

As Thanksgiving approaches in the US, a familiar scenario will play out—individuals will partake in celebrations featuring large plates of dinner and dessert delicacies. Soon after this indulgence, they may find themselves craving a nap. This phenomenon brings up a common question: Why does Thanksgiving dinner make people sleepy?

A common misconception is that high tryptophan levels in turkey are the culprit. As tryptophan is a precursor to melatonin, a hormone that helps regulate sleep-wake cycles, the hypothesis is that eating more tryptophan-containing turkey causes this post-meal fatigue.

However, this rationale doesn’t stack up, since many other foods that people eat regularly also contain similar levels of tryptophan, and nobody complains about needing a nap after finishing off a fruit salad with cherries.¹ “In general, the amount of tryptophan and even melatonin in food is not enough to alter your sleep,” said Claudia Moreno, a chronobiologist at the University of São Paulo.

Although tryptophan and turkey aren’t the culprits behind Thanksgiving naps, diet does still have an effect on sleep.² Moreno previously showed that diets high in carbohydrates and fats induce more fatigue in truck drivers than those high in vegetables and fiber.³ Many other human studies also demonstrated that the composition of carbohydrate, fat, and protein content in meals influences the propensity to sleep.^4,5 Alcohol also increases drowsiness, although it worsens overall sleep quality.^6,7

While researchers don’t have definitive answers yet, “[The] consensus is, don’t eat too much,” Moreno summarized. “You need to balance a little bit the amount of alcohol and food you eat,” she said.

To dig into the details of this diet-sleep linkage, some researchers turned to animal models. William Ja, a neuroscientist studying behavior at The Herbert Wertheim University of Florida Scripps Institute for Biomedical Innovation and Technology, and his group demonstrated that flies that consumed meals high in protein or high in salt slept more compared to flies that ate a more balanced meal.⁸

Additionally, they identified that one type of neuron sensed and responded to the protein content and triggered sleep in these insects. They suspect that the other triggers may have similar circuitry. “You might imagine a sensor for meal volume connected to the sleep circuits of the brain to make you sleepy,” Ja explained.

Although flies are a long leap from humans, many other mechanisms are conserved between the two species, so it’s possible that a similar metabolite sensor or stretch receptors in the stomach could be triggering the fatigue many people feel after finishing their plate.

Understanding why this process exists, though, is difficult to tease apart. However, given the observations of post-meal fatigue across species, Ja is confident that there is a function. “It suggests that it’s an important evolutionary conserved behavior that must do something for us,” Ja said.

Digestion is an energy intensive process, so promoting rest could be one mechanism to direct resources to break down the abundance of food, as well as to conserve energy in general.⁹ Studies in mice demonstrated that neurons that recognize food needs regulate sleep behaviors, indicating that this linkage maintains homeostasis.¹⁰ Alternatively, given the role of sleep in memory and learning, this post-meal rest could be an evolutionary leftover to consolidate information about food sources.¹¹

However, holiday revelers are not doomed to spend their visits on a pillow. Besides minimizing the size of one’s plate to reduce the nap craving, according to Moreno, the timing and duration of meals also influences drowsiness. “Try to eat and stop eating, and then you can have time to digest this food and not become like an eater for four hours,” she said. Keeping meals close to one’s normal mealtimes and not right before bed can also help. If a post-meal nap is unavoidable, then Moreno said that restricting this rest period to 30 minutes will prevent one’s sleep schedule from too much disruption.