Many people associate the drowsiness felt after large holiday meals, often called a “food coma,” directly with turkey. This popular belief suggests a unique sleep-inducing property within the poultry. This prompts questions about the specific components in turkey that might cause such an effect.
Unpacking Tryptophan
Tryptophan is an essential amino acid, meaning the human body cannot produce it and must obtain it through diet. It serves as a building block for proteins and plays a role in various bodily functions. Tryptophan is a precursor to several important molecules, notably serotonin and melatonin. Serotonin is a neurotransmitter that influences mood, well-being, and sleep, while melatonin is a hormone that regulates the sleep-wake cycle.
While turkey contains tryptophan, many other protein-rich foods contain comparable or even higher amounts. These include chicken, cheese, eggs, fish, nuts, and seeds. The body converts tryptophan into serotonin and then melatonin. This conversion contributes to its association with sleep and its role in promoting relaxation.
Why Turkey Alone Doesn’t Make You Sleepy
The idea that tryptophan in turkey directly causes sleepiness is a persistent misconception, as its ability to induce drowsiness on its own is limited. This is due to the complex process of how amino acids, including tryptophan, reach the brain.
All amino acids, whether from turkey or other protein sources, compete for transport across the blood-brain barrier. This barrier is a highly selective mechanism that controls what enters the brain from the bloodstream. When consuming turkey, you ingest many different amino acids simultaneously. Tryptophan is relatively less abundant compared to other larger amino acids in a typical protein-rich meal.
The more plentiful amino acids effectively outcompete tryptophan for entry into the brain via shared transport systems. Even if a meal contains tryptophan, other amino acids prevent a significant amount from crossing the blood-brain barrier to increase serotonin and melatonin sufficiently for immediate sleepiness. Therefore, tryptophan in turkey, when consumed as part of a meal with other proteins, is unlikely to be the sole or primary cause of post-meal drowsiness.
The Real Reasons for Post-Meal Drowsiness
The feeling of sleepiness after a large meal, often referred to as a “food coma,” is influenced by several physiological factors. One significant factor is the sheer volume of food consumed. Large meals require substantial digestive effort, which diverts blood flow towards the gastrointestinal system to aid in breaking down nutrients. This increased digestive activity can contribute to a feeling of fatigue.
Carbohydrate intake also plays a role in post-meal drowsiness. Meals high in carbohydrates, such as mashed potatoes and stuffing, lead to a rapid increase in blood sugar. This triggers the pancreas to release insulin, which helps transport glucose into cells for energy. Insulin also promotes the uptake of many amino acids from the bloodstream into muscle tissue, but tryptophan is not as readily taken up by muscles. This can reduce the competition for tryptophan to cross the blood-brain barrier, potentially allowing more tryptophan from any food source to enter the brain, where it can be converted to serotonin and then melatonin.
The activation of the parasympathetic nervous system, often called the “rest and digest” system, also contributes to post-meal relaxation. This system becomes more active during digestion, promoting a state of calm and reducing alertness. Additionally, alcoholic beverages, frequently consumed with large meals, are central nervous system depressants that can significantly enhance feelings of drowsiness.