You’ve heard it before – tryptophan will make you sleepy! That’s why after a Thanksgiving meal you’re tired. And with the rise of “sleepy girl mocktails” made with tart cherry juice, the hype about tryptophan is real. Recently, I saw one article how how tryptophan does NOT make you sleepy. So I decided to dive in and see what the science tells us.
What is tryptophan?
Tryptophan is an essential amino acid, meaning our bodies cannot make it on its own, and we must obtain it from food. Once consumed, it goes through processes to be transformed into several substances, such as: serotonin, melatonin, and nicotinamide (niacin) (1).
It has been proposed to help with sleep, and supplementing with >1g has been shown to shorten wake after sleep onset (3).
Why does it make you sleepy?
Melatonin and serotonin are produced from tryptophan, so by transformation of this amino acid once ingested, yes – it can make you sleepy.
There are a few caveats we can go through here.
Tryptophan can pass through the blood-brain barrier. But so make all large neutral amino acids (LNAAs). These include histidine, isoleucine, leucine, methionine, threonine, phenylalanine, valine, tyrosine, and of course, tryptophan. This means that all of these LNAAs are competing to go across the blood-brain barrier. In theory, less LNAAs attempting to cross would allow for more tryptophan to enter ,and be available for melatonin and serotonin production.
One study promotes consuming carbohydrate rich foods with tryptophan containing food. This elicits insulin release, which promotes muscle protein synthesis (MPS), which (hopefully) would shuttle some of the LNAAs to the muscle instead of the blood-brain barrier, leaving more tryptophan available (2).
what foods have tryptophan?
Foods with tryptophan include (2):
Cheddar cheese: 574mg tryptophan per 100g serving
Salmon, tuna: 280-315mg per 100g serving
Wheat germ: 398mg per 100g serving
Roasted Soybeans: 575mg per 100g serving
Firm tofu: 235mg per 100g serving
Pumpkin and squash seeds: 576mg per 100g serving
Chia seeds: 436mg per 100g serving
Lentils: 81mg per 100g serving
Hazelnuts, almonds, cashews, pistachios: 190-255mg per 100g serving
Chicken breast: 404mg per 100g serving
Turkey breast: 287mg per 100g serving
Whole egg: 167mg per 100g serving
You can see, chicken breast actually has MORE tryptophan than turkey does per 100g serving (roughly 3.5oz for each).
As far as tart cherries go, they do not contain tryptophan, but they do melatonin. However, *tomatoes (minimum 773ng) actually contain more melatonin than tart cherries (135ng) (2). So that “sleepy girl mocktail” with tart cherry juice should really be a “sleepy girl alcohol free bloody mary”, or good old fashioned tomato juice.
So after a Thanksgiving meal, yes you could be tired because of the tryptophan, but you also be tired due to the large amount of food you just ate!
*depends of variety and season
references:
(1) Friedman, Mendel. “Analysis, nutrition, and health benefits of tryptophan.” International Journal of Tryptophan Research 11 (2018): 1178646918802282.
(2) Zuraikat, Faris M., et al. “Sleep and diet: mounting evidence of a cyclical relationship.” Annual Review of Nutrition 41 (2021): 309-332.
(3) Sutanto CN, Loh WW, Kim JE. The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression. Nutr Rev. 2022 Jan 10;80(2):306-316. doi: 10.1093/nutrit/nuab027. PMID: 33942088.
