Aaron Carroll debunks it:.
The truth is, turkey is not to blame for your sleepiness. Chicken and ground beef contain almost the same amount of tryptophan as turkey about 350 milligrams per 4 ounce serving. While you might have heard someone claim that turkey made them drowsy, you have probably never heard someone say that chicken, ground beef, or any other meat made them sleepy. Swiss cheese and pork actually contain more tryptophan per gram than turkey, and yet the American classic, a ham and cheese sandwich, somehow escapes blame.
The reason you get drowsy:
Large meals have been shown to cause sleepiness regardless of what is eaten because the body increases blood flow to the stomach, and decreases blood flow and oxygenation to the brain. Meals both high in proteins or in carbohydrates may cause drowsiness. And don’t forget about the booze. One or two glasses of wine, especially for people who only drink occasionally, can increase drowsiness.