Why does Thanksgiving dinner make some people sleepy?

AAs Thanksgiving approaches in the United States, a familiar scenario will play out: individuals will partake in celebrations that feature large plates of dinner and dessert delicacies. Soon after this indulgence, they may feel like taking a nap. This phenomenon raises a common question: Why does Thanksgiving dinner make people sleepy?

A common misconception is that high levels of tryptophan in turkey are responsible. Since 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 sleepiness.

However, this reasoning is not valid since many other foods that people eat regularly also contain similar amounts of tryptophan, and no one complains about needing a nap after finishing 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 for Thanksgiving naps, diet still has an impact on sleep.² Moreno previously showed that diets high in carbohydrates and fat caused more fatigue in truck drivers than diets high in vegetables and fiber.³ Many other human studies have also shown that the composition of carbohydrate, fat and protein content in meals influences sleep propensity.^4.5 Alcohol also increases sleepiness but worsens overall sleep quality.^6.7

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

To study the details of this connection between diet and sleep, some researchers turned to animal models. William Ja, a neuroscientist who studies behavior at the Scripps Institute for Biomedical Innovation and Technology at Herbert Wertheim University of Florida, and his group showed that flies that ate high-protein or high-salt meals slept more than flies that ate a more balanced meal took in.⁸

In addition, they found that one type of neuron sensed the protein content, responded to it, and triggered sleep in these insects. They suspect that the other triggers may have similar circuits. “You could imagine a food quantity sensor that connects to the brain’s sleep circuits to make you sleepy,” Ja explained.

Although flies are a big step away 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 trigger the fatigue that many people feel after finishing their plate.

However, it is difficult to understand why this process exists. However, given observations of post-eating fatigue in all species, Ja is confident there is a function. “This suggests that it is an important, evolutionarily conserved behavior that must do something for us,” Ja said.

Digestion is an energy-intensive process, so promoting rest could be a mechanism to use resources to break down food abundance and generally conserve energy.⁹ Studies in mice showed that neurons that detect food needs regulate sleep behavior, suggesting that this link maintains homeostasis.¹⁰ Alternatively, given the role of sleep in memory and learning, this post-meal rest period could be an evolutionary holdover for consolidating information about food sources.¹¹

However, vacationers are not condemned to spend their visits on a pillow. In addition to minimizing plate size to reduce the urge to nap, Moreno says the timing and length of meals also influence sleepiness. “Try to eat and stop eating, then you’ll have time to digest that food and not become like an overeater for four hours,” she said. It may also be helpful to keep meals close to normal meal times rather than right before bed. If a nap after eating is unavoidable, Moreno says limiting that rest time to 30 minutes protects your sleep cycle from being disrupted too much.