What's the Hormone in Turkey That Makes You Tired?

December 29, 2025 •

3 min read

While many blame the amino acid tryptophan for making them sleepy after eating turkey, experts reveal it is not the primary culprit. The truth behind the infamous 'food coma' is more complex and involves a combination of factors, including large portion sizes and other foods consumed during the meal.

Quick Summary

The myth that tryptophan in turkey causes tiredness is widespread, but science points to other factors like large meals, high carbohydrate intake, and alcohol consumption as the real reasons for post-dinner sleepiness. Contrary to popular belief, turkey does not contain exceptionally high levels of tryptophan compared to other protein sources, and the body's digestive processes naturally shift energy resources, leading to a feeling of lethargy.

Key Points

Tryptophan is not a hormone: The substance often blamed is an amino acid, not a hormone, and is found in many protein-rich foods.
Turkey is not uniquely high in tryptophan: Many other common foods, including chicken and cheese, contain similar or higher levels of this amino acid.
The blood-brain barrier is a gatekeeper: After a protein-heavy meal, tryptophan struggles to cross into the brain because it competes with other amino acids.
Large meals are the real cause: Overeating requires significant energy for digestion, diverting blood flow from the brain and causing fatigue.
Carbohydrates play a major role: High-carb foods trigger an insulin release and a subsequent blood sugar crash, leading to lethargy.
Alcohol is a depressant: Drinking alcohol with a meal adds to the sedative effect and exacerbates feelings of sleepiness.
Circadian rhythms contribute: Eating a large meal in the evening aligns with the body's natural sleep cycle, increasing drowsiness.
Balance is key: To reduce post-meal sleepiness, focus on mindful eating, balanced portions, and moderation of carbs and alcohol.

Debunking the Tryptophan Myth

For years, the tryptophan myth has been a popular explanation for why we feel drowsy after a big meal, particularly on holidays like Thanksgiving. The theory suggests that turkey's high concentration of this essential amino acid leads to increased production of serotonin and melatonin, the body's sleep-regulating hormones. However, this is largely a misconception.

The Science Behind Tryptophan and the Blood-Brain Barrier

While turkey does contain tryptophan, it's not present in high enough concentrations to have a significant sleep-inducing effect on its own. The issue lies in the body's complex biological processes. Tryptophan has to compete with numerous other amino acids to cross the blood-brain barrier and enter the brain. After a large meal rich in protein, this competition is fierce, and tryptophan often loses, preventing a surge in sleep-inducing chemicals.

The Real Culprits Behind Your Post-Meal Sleepiness

The real reasons for feeling tired after a large meal are far less glamorous than a single hormone. The phenomenon known as the 'food coma' is actually a combination of several physiological factors working in concert.

1. Overeating and Digestive Processes

Eating a large, calorie-dense meal is the primary reason for post-meal fatigue. When you overeat, your body directs a significant amount of blood flow to your digestive system to process the food. This diversion of blood and energy away from the brain and other parts of the body can lead to a feeling of sluggishness and reduced alertness. The larger and richer the meal, the more pronounced this effect will be.

2. The Role of Carbohydrates

Thanksgiving meals are typically laden with carbohydrates, from mashed potatoes and stuffing to pies and other desserts. Carbohydrates trigger an increase in blood sugar, which prompts the pancreas to release insulin. This insulin spike helps move glucose and other amino acids out of the bloodstream, leaving a clearer path for the remaining tryptophan to enter the brain. The subsequent blood sugar crash contributes significantly to feelings of lethargy and sleepiness.

3. Alcohol Consumption

Many people enjoy alcoholic beverages with their holiday meals. Alcohol is a depressant that slows down the central nervous system, which can induce drowsiness and amplify the effects of the other factors contributing to fatigue. Combined with a large meal, alcohol consumption can make a post-dinner nap nearly irresistible.

4. The Timing of the Meal

Often, holiday feasts are eaten in the late afternoon or early evening, a time when our natural circadian rhythms are already beginning to wind down. The combination of a large meal and the body's natural cycle can enhance the feeling of sleepiness. The change in seasons and shorter daylight hours in the northern hemisphere also contribute to this effect, as melatonin production increases in the evening.

Turkey's Tryptophan Content: A Comparison

While the focus often falls on turkey, many other common foods contain similar or higher levels of tryptophan. The table below illustrates how turkey compares to other protein sources.


Food (per 100g)	Approximate Tryptophan (mg)	Notes
Roasted Turkey Breast	410	A standard portion contains a modest amount of tryptophan.
Roasted Chicken Breast	431	Slightly higher tryptophan content than turkey.
Roasted Pumpkin Seeds	576	One of the highest dietary sources of tryptophan.
Cheddar Cheese	500+	Also a significant source, yet not blamed for 'cheese comas'.
Ground Pork	416	Comparable to turkey in tryptophan levels.
Tuna	300+	Another protein source rich in tryptophan.
Soybeans	592	A plant-based source with very high tryptophan content.

This comparison clearly shows that turkey is not uniquely high in tryptophan, further disproving the popular myth. It's the overall meal composition, not just the turkey, that matters.

Conclusion: Enjoy Your Turkey, But Mind the Rest

To sum up, the idea that a specific hormone in turkey makes you tired is a misconception fueled by the tryptophan myth. While tryptophan is present in turkey, it's not the primary cause of post-meal drowsiness. Instead, the infamous 'food coma' results from a combination of factors: overeating, a high intake of carbohydrates, alcohol consumption, and natural sleep cycles. By understanding the true reasons behind your fatigue, you can better manage your portion sizes and overall meal composition to avoid feeling excessively sleepy after a large feast. So go ahead and enjoy your turkey, but consider balancing it with more vegetables and being mindful of your carb and alcohol intake.

For more information on nutrition and metabolism, consider consulting resources like the Cleveland Clinic's health library for credible information on dietary myths and facts.

Frequently Asked Questions

The 'food coma' is primarily caused by a combination of overeating, high carbohydrate intake, and alcohol consumption, which diverts blood flow to the digestive system and causes fluctuations in blood sugar.

No, tryptophan is an essential amino acid and is the same regardless of the food source. The amount of tryptophan in turkey is comparable to or lower than other protein sources like chicken, pork, and cheese.

Consuming large amounts of carbohydrates causes a spike in blood sugar, which triggers insulin release. The subsequent crash in blood sugar levels is a major contributor to feelings of lethargy and tiredness.

Unlike a pure tryptophan supplement, the tryptophan in turkey is consumed alongside many other amino acids. These amino acids compete to cross the blood-brain barrier, significantly limiting the amount of tryptophan that can reach the brain and produce sleep-inducing effects.

Yes, alcohol is a depressant that slows down the nervous system and is a well-known inducer of drowsiness. Combining it with a large, heavy meal will amplify feelings of fatigue.

Tryptophan is a precursor to the neurotransmitter serotonin and the hormone melatonin, both of which help regulate sleep. However, the amount of tryptophan from a typical turkey meal is not enough to dramatically increase these levels.

To combat post-meal fatigue, you can try eating smaller, more balanced portions, limiting high-carbohydrate foods and alcohol, staying hydrated, and taking a short walk after eating to aid digestion.

Not necessarily. Other factors such as pre-existing exhaustion, holiday stress, and the body's natural sleep-wake cycle (circadian rhythm) can all contribute to feeling sleepy after a large meal.