Most of us have heard about the relaxing benefits of drinking a warm glass of milk before bed, or have experienced the inevitable drowsiness that results from spending a couple of hours at a Thanksgiving table. Many foods that induce drowsiness contain a naturally occurring substance called tryptophan. Tryptophan, one of 20 so-called amino acids, is found not only in poultry and dairy products, but also in beef, fish, peanuts, and whole grains. What role does this chemical play and how much effect do tryptophan-rich foods really have on our ability to stay awake for dessert?
Evidence for the Health Claim
When tryptophan is absorbed into the blood stream, it is ultimately converted into serotonin, a neurotransmitter with a variety of effects, one of which is to calm certain areas of the brain leading to a sensation of drowsiness. This presumably accounts for why you may see a number of family members nodding off after eating a lot of turkey at the big Thanksgiving dinner.
In fact, so secure was the belief in the sleep-inducing benefits of tryptophan that it was manufactured as a dietary supplement in the 1980s to treat people suffering from insomnia .
Evidence Against the Health Claim
Studies carried out by Simon Young, PhD, a research psychologist at McGill University in Montreal, have shown that while tryptophan can make you sleepy, the amount of it that the body is able to process from eating a turkey dinner is actually less than is necessary to cause much of an effect. One reason for this is that tryptophan has to compete with other, more abundant amino acids in the blood stream to gain entry to the brain.
Young also points out that turkey contains substantially less tryptophan than other protein sources and that the reason for the Thanksgiving “post-turkey torpor” is more likely the result of drinking alcohol and eating too many starchy and sugar-laden carbohydrates.
Other scientific research has suggested that tryptophan would have a far more significant effect if turkey was eaten on an empty stomach, when tryptophan can be most readily absorbed into the blood stream, and that even then, the level of tryptophan found in a reasonable serving would be far too low to be sleep-inducing.
It is also important to note that the US Food and Drug Administration (FDA) banned the import and use of tryptophan as a dietary supplement in 1990, after about 5,000 people who were taking it developed eosinophilia-myalgia, a muscle disorder that resulted in the death of at least 37 people. Although a contaminant, rather than the tryptophan itself, was to blame for these adverse effects, the product is still not widely available in the US.
While research supports the potential sleep-inducing effects of drinking a warm glass of milk or eating a turkey dinner, those effects are apparently compromised when too much of too many different types of food are consumed in the same meal. Therefore, one could argue that the best way to reap the benefits of tryptophan may well be to snack individually on tryptophan-rich foods (eg, turkey, chicken, fish, cottage cheese, bananas, eggs, nuts, avocados, milk, cheese, beans, and peas) on an empty stomach an hour or so before bed.