I just came across of dubious food fact about bananas. The tryptophan in bananas has sleep-inducing properties. Therefore, if you eat a banana before going to bed it will help you sleep. Anyone who has suffered bouts of insomnia will not have to be told that this is highly unlikely, but what about turkey? Everyone knows that Thanksgiving turkey is full of tryptophan and this is why you always feel so sleepy after a holiday meal.
As you know, everyone knows is certainly how facts are born and propagated, but these are not the kind of objective facts I’m concerned with here on CulinaryLore. I’m concerned with actual scientific fact. So, what follows is a two-part series on tryptophan. This first article cover holiday meals and sleepiness from tryptophan in turkey. Afterward, I will discuss warm milk and tryptophan, tryptophan supplements, and safety.
Many people, with or without any scientific evidence, are firmly convinced that the particular foods they eat have a direct influence on their mood, anxiety level and alertness. Perhaps the most well known manifestation of this belief is that certain foods make us sleepy, particularly those with high levels of the amino acid tryptophan. Turkey, at least in the US, is thought to cause sleepiness due to it’s high level of tryptophan and this is said to explain why we are so desperate for a nap after Thanksgiving dinner.
The hormone melatonin, or N-acetyl 5-methoxytryptamine, is derived from the amino acid tryptophan in the brain and tryptophan is also used to synthesize the excitatory neurotransmitter serotonin, or 5-OH tryptamine. The level of these substances in the brain certainly have an influence on our state of restfulness or restlessness.
Nevertheless, the turkey tryptophan connection has been largely debunked. The reason for this, however, is generally misunderstood or misreported. The levels of tryptophan in turkey are comparable to other meats. So, for example, a pork chop contains as much, or more tryptophan as an equivalent amount of turkey, meaning turkey and it’s tryptophan content alone cannot be taken to be the culprit for the drowsiness so many of us experience after the holiday meal.
Holiday Meals, Tryptophan, and Sleepiness: It’s the Carbs
The actual culprit seems to be the huge carbohydrate blast, including alcohol, that we usually get during these feasts. These meals contain a much larger ratio of carbohydrate to protein when the starches, vegetables, deserts, and alcohol is factored in. A carbohydrate rich meal can increase levels of brain tryptophan and serotonin. As a matter of fact, this can happen even if the meal completely lacks tryptophan.
What happens is that the release of insulin from the carbohydrate ingestion causes the uptake of most of the large neutral amino acids such as valine, leucine, tyrosine, and phenylalanine into muscle cells, leaving tryptophan behind in the blood plasma. Just why tryptophan levels do not decline like the LNAA’s is not exactly clear but it may be due to it’s binding to albumin molecules on sites that were freed when the free fatty acids occupying them were also released by insulin action. As a result, after this large carbohydrate infusion, plasma tryptophan levels are relatively high.
The LNAA’s and tryptophan usually compete for a common carrier molecule for transport across the blood-brain barrier into the neurons. So, when the plasma levels of the LNAA’s decrease significantly from a high carbohydrate meal, tryptophan gets a free ride, causing neuronal levels of serotonin to increase. This is what makes us sleepy after a large holiday meal, one that is typically loaded with carbohydrates.
How Much Turkey Would It Take to Make You Sleepy?
So, if these meals really do make us sleepy it is the carbohydrate that is thought to be responsible, regardless of protein levels in the meal. Still, it has often been reported that turkey doesn’t make us sleepy “because there isn’t enough tryptophan in it”. This, further, has led to statements concerning the amount of turkey it would take to actually make one sleep due to direct action. I have read statements such as “it would take 40 pounds of turkey to get enough tryptophan to make you sleepy”.
What this type of calculation is based on is not clear but it is likely an effort to correlate the amount of tryptophan in turkey with the typical dosage that people take in supplement form. This is a mistake. The amount of turkey or any other protein source you eat should have no influence on sleep as the intake of LNAA’s from this protein source will result in an increase of plasma levels of these amino acids. This will cause competition for brain-uptake of these aminos to increase since, again, the LNAA’s and tryptophan compete for a common carrier. So a large protein intake causes brain levels of tryptophan (and serotonin) to decrease, not increase. 1Groff, James L., and Sareen Gropper. “Chapter 16: Nutrition and the Central Nervous System.” Advanced Nutrition and Human Metabolism. Belmont, Calif. ; London: Wadsworth, 2000. 536-40. Print.
Warm Milk and Tryptophan for Sleep
Warm milk before bed is a tried and true remedy for sleep. Except for the fact that its more tried than true. While many may find it relaxing, if not sleep inducing, others will get no results at all. But how could warm milk work if the amount of tryptophan, as we’ve seen from the turkey discussion, doesn’t really matter?
It may be the same mechanism as above, which is why this doesn’t really rate a seprate article. How the milk being warm affects this is unknown, if it affects it at all. It is true that lactose, the carbohydrate in milk reacts to very high temperature treatment by browning and isomerization. The browning is called the “Maillard reaction” and this occurs between the lactose and the milk’s proteins. The flavor and color of milk is affected by the Maillard reaction and a bitter taste occurs. The isomerization causes the lactose (bonded galactose and glucose) to be rearranged to lactulose which is one galactose molecule linked to one fructose molecule. However, this isomerization occurs at very high temperatures, upwards of 275 degrees farenheith (135 degress celcius) and would probably not affect the availability of carbohydrate or influence the carbohydrate- serotonin reaction. Still, it is at least feasible that milk or any moderately high carbohydrate intake before bedtime could influence sleepiness. This would presumably occur regardless of the protein level in the food and the tryptophan content of milk has no bearing, warm or not. 2By Kurt. “Carbohydrates.” Cornell University Milk Facts Website. Web. 14 Sept. 2010. <http://www.milkfacts.info/Milk Composition/Carbohydrate.htm>.)),3By Kurt. “Heat Treatments and Pasteurization.” Cornell University Milk Facts Website. Web. 14 Sept. 2010. <http://www.milkfacts.info/Milk Processing/Heat Treatments and Pasteurization.htm#PastConds>.
Milk, for its part, at least has more tryptophan than the food I started with, banana. One-hundred grams of milk contains about 80 mg trytophan, while bananas contain about 10 mg. Turkey does contain a lot more than either of these at around 240mg per 100 grams. I won’t bother converting this into volume measurements, because it really doesn’t matter when you consider that egg whites contain an entire gram of tryptophan per 100 grams, making it a juggernaught compared to these others. Eggs also contain a full complement of essential amino acids which will compete for uptake.
So, if tryptophan is to have a chance of working any kind of magic, it probably needs to be taken alone. The next article covers tryptophan supplementation.
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|1.||↲||Groff, James L., and Sareen Gropper. “Chapter 16: Nutrition and the Central Nervous System.” Advanced Nutrition and Human Metabolism. Belmont, Calif. ; London: Wadsworth, 2000. 536-40. Print.|
|2.||↲||By Kurt. “Carbohydrates.” Cornell University Milk Facts Website. Web. 14 Sept. 2010. <http://www.milkfacts.info/Milk Composition/Carbohydrate.htm>.))|
|3.||↲||By Kurt. “Heat Treatments and Pasteurization.” Cornell University Milk Facts Website. Web. 14 Sept. 2010. <http://www.milkfacts.info/Milk Processing/Heat Treatments and Pasteurization.htm#PastConds>.|