Tryptophan can make someone sleepy for several different reasons, though in general the tryptophan found in turkey is not solely responsible for feelings of sleepiness after a large holiday meal. When consumed alone, tryptophan in food can make you sleepy, though this typically has to be consumed with little or no other food to be effective. If eaten with other foods, then the amount of food eaten will often impact how sleepy a person feels afterward, and high amounts of carbohydrates can also increase how sleepy someone feels after eating turkey or similar dishes.
Many people often feel sleepy or tired after eating a large holiday meal, such as at Christmas or the American holiday of Thanksgiving. Since these meals often include turkey, the tryptophan found in turkey is frequently blamed for these feelings of sleepiness after the conclusion of the meal. The reality, however, is that turkey has relatively low amounts of tryptophan in it, equivalent to other poultry such as chicken, and far less than foods like parmesan cheese or sesame seeds. Tryptophan can make a person feel sleepy or tired, but this typically occurs for one of two reasons.
When consumed on an otherwise relatively empty stomach, without other foods, foods rich in tryptophan can make a person sleepy by producing serotonin and melatonin, both chemicals involved in a person’s sleep cycles. This is why a midnight snack consisting of a small turkey sandwich or a small helping of turkey can effectively help a person fall asleep. When consumed with other foods, however, the turkey itself is typically not the sole culprit in causing sleepiness. Much of the sleepiness felt after a large holiday meal is due to the other foods that are eaten as well.
A holiday meal of turkey is often accompanied by other large amounts of food, many of them high in carbohydrates such as dinner rolls, mashed potatoes, stuffing, and pie. These carbohydrates cause the tryptophan introduced into a person’s system to be more easily absorbed into the central nervous system of the eater. This in turn creates higher levels of serotonin and melatonin. It is the high amounts of carbohydrates consumed with turkey that allow the tryptophan to contribute to feelings of sleepiness.
The average holiday meal, especially Thanksgiving in the US, is also extremely high in calories and fat, and often accompanied by alcohol. This large meal requires a great deal of energy for the body to digest, and blood is diverted from other systems in a person’s body to the stomach to help with digestion. The rest of a person’s body, therefore, has less energy and less oxygenation, causing feelings of sleepiness and lethargy. Alcohol that is consumed with the large meal can also act as a sedative in the person’s system, contributing to his or her sleepiness.