text: In this instace, lore almost interects with science.  Turkey does contain Tryptophan, an amino acid which is a natural sedative.  But trytophan doesn't act on the brian unless it is taken on an empty stomach with no protein present, and the amount eaten even during a holiday feast is generally too small to have an appreciable effect.  That lazy, lethargic feeling so many are overcome by at the conclusion of a festive season meal is most likey due to the combination of drinking alcohol and over eating a carbohydrate-rich repast, as well as some other factors.