Tryptophan is an essential amino acid. Your body needs it in order to make protein and important chemicals like serotonin. But you can’t make tryptophan yourself; you need to get it in your diet. There are a number of dietary sources of tryptophan, including nuts, seeds and fish. Turkey is also high in tryptophan.
Tryptophan’s Role in Your Body
Tryptophan serves a number of purposes in your body. Your body uses tryptophan to synthesize niacin, which can help ensure that you’re getting enough niacin even when you’re not eating adequate amounts of the B vitamin. Your body also uses tryptophan to make serotonin, a neurotransmitter that’s responsible for a number of body functions, mostly to do with mood and sleep. Tryptophan deficiency can lead to low serotonin levels, which can cause depression, anxiety and insomnia, as well as problems in concentration and focus, overeating and other appetite problems, impulsiveness and impatience.
Foods High in Tryptophan
There are a number of foods that are high in tryptophan, including nuts and seeds, oily fish, diary products, shellfish, bananas and soy products. A number of meats are high in tryptophan, including turkey.
Does Turkey Make You Sleepy?
Popular wisdom would have it that since turkey is high in tryptophan, it’s the reason why so many people feel groggy and sleepy after eating Thanksgiving dinner. Your body does use tryptophan to make serotonin, which plays a key role in your ability to sleep. You also use tryptophan to make melatonin, the hormone your brain produces just before and during sleep. However, that doesn’t mean that eating foods high in tryptophan makes you sleepy.
Eating foods, like turkey, that are high in tryptophan will increase levels of tryptophan in your blood, but that doesn’t mean that all that tryptophan makes it into your brain, where it can be converted into serotonin and melatonin. The tryptophan you eat has to compete with all the other amino acids in your food to cross the brain blood barrier and gain access to your brain–so most of it remains in your blood. The tryptophan that does make it to your brain won’t be converted to melatonin right away. Your brain makes melatonin from serotonin, so eating a turkey dinner doesn’t increase melatonin production in your brain, until later, when you fall asleep.
Scientists believe that it’s actually the carbohydrates in your meal that make you feel sleepy. Carbohydrates don’t contain tryptophan, but eating them does cause an increase in blood sugar, which stimulates your pancreas to produce insulin. Insulin doesn’t just lower blood sugar levels; it also lowers the levels of most amino acids in your blood, except for tryptophan. This means that eating tryptophan in combination with carbohydrates makes it easier for tryptophan to reach your brain, since there aren’t so many other amino acids struggling to cross the brain blood barrier. So, really, it isn’t the turkey itself that makes you sleepy, but the large number of carbs you eat along with the turkey.