It is a commonly held belief that the L-tryptophan contained in turkey makes a person sleepy. However, research has shown that sleepiness after eating a holiday meal is more likely due to overindulgence, and is exacerbated by alcohol consumption.
L-tryptophan is an amino acid found in foods such as fish, poultry and dairy products. Tryptophan ingestion does assist in the production of serotonin, which creates feelings of relaxation and well-being. However, turkey does not contain any more tryptophan than other varieties of poultry, and actually has less than chicken. Because carbohydrates directly affect serotonin levels, sleepiness after a holiday meal is more likely the result of eating large quantities of stuffing, cranberry relish and dinner rolls.