A man pulls a turkey out of a deep fryer at Texas Stadium in Dallas, Nov. 27, 2008. Contrary to popular belief, the tryptophan in turkey doesn't cause fatigue after eating. Reuters

The Thanksgiving holiday typically brings an abundance of food, especially turkey. And anyone who has consumed a Thanksgiving meal knows the post-eating urge to sleep that follows shortly after. But contrary to popular belief, turkey and its tryptophan aren't the main culprits.

Tryptophan is an amino acid found in turkey that turns into a vitamin called niacin when consumed. Niacin, in turn, creates serotonin, a hormone responsible for sleep. But tryptophan is just one of many amino acids that make its way to the brain from food, especially during a large and varied meal like the one eaten during Thanksgiving.

Tryptophan is overpowered by the other amino acids and therefore has little effect. However, when eaten with large amounts carbohydrates, the carbs create insulin, which removes all the other amino acids and leaves only tryptophan to do its work. Despite that, it's still not enough to cause extreme fatigue, according to the National Sleep Foundation.

The real reason for fatigue on turkey day is the giant meal. The irresistible Thanksgiving nap is more likely a result of overconsumption of heavy foods like stuffing and mashed potatoes, not the tryptophan in turkey. The composition of a meal and increased blood flow to the gastrointestinal tract can also cause fatigue.

Turkey is served at a homeless shelter in Los Angeles, Nov. 25, 2009. Reuters

Turkey gets a bad rap, but chicken and beef contain almost as much tryptophan. All three meets contain about 350 milligrams in every four-ounce serving. By contrast, recommendations for tryptophan supplements to aid in sleep are about 500 to 1,000 milligrams per dose.

Swiss cheese and pork contain more tryptophan than turkey. Other dietary staples like eggs, nuts and salmon also have significant amounts of the amino acid.

Tryptophan is a necessary amino acid. The body needs it to function properly. Without tryptophan, mood swings and depression can occur. So load up on turkey this Thanksgiving, just don't blame the poultry when you can't resist the urge to sleep.