What's in my milk? | Tryptophan

Happy Thanksgiving, friends! With the Thanksgiving holiday upon us, it is the perfect time to kick off our new series on the various components in human milk starting with the amino acid, Tryptophan!  


What is tryptophan? 

Tryptophan, also known as l-tryptophan, is an essential amino acid that comes from our diet and it is needed for a variety of roles in the body. Some of the most well known responsibilities of tryptophan include promoting infant development and helping make melatonin and serotonin which regulate processes like our mood and sleep pattern (1).

Perhaps tryptophan sounds familiar to you - ever heard of a post-Thanksgiving "turkey coma?" Turkey, fish, eggs and dairy are some of the main sources that contain l-tryptophan and many people believe that the post-Thanksgiving dinner drowsiness is from all the tryptophan from turkey! But is this fact or fiction?!

Ready for it? It's FICTION! Turkey actually doesn't contain an especially high amount of tryptophan and the Thanksgiving sleepies may simply be due to an extra large, carb-heavy meal (2)! 


Tryptophan IS IN HUMAN MILK.

Our breast milk contains components that help regulate our baby's circadian rhythms AKA baby's internal clock regulating when they are sleepy or awake (3). One of these main sleep-inducing components is tryptophan and the levels of tryptophan found in our milk constantly changes depending on the time of day. Here is some cool science for you - when we're pregnant, baby's sleep pattern is influenced by hormones in our body like cortisol and melatonin, but once they are born it takes about 2-4 months for their own bodies to regulate the sleep-wake cycle which is why many newborns have their days and nights switched (3)! Researchers believe that human milk and those sleep-inducing components like tryptophan helps to regulate the sleep-wake cycle while baby's body is still trying to figure out life outside the womb (3). 

Human milk is ever-changing -- your milk in the morning will be slightly different than your milk in the evening and your milk tomorrow will be a little different than your milk today. Our bodies and babies are quite remarkable in that our milk changes based on what our babies need. This includes changing the levels of sleep-inducing components like tryptophan based on the time of day! 

Yes, you read that right! Human milk can change in composition throughout the day to make baby sleepier at night. In fact, the levels of tryptophan in human milk naturally fluctuate with higher levels in the evening reaching its peak concentration at 3am and its lowest at 3pm and this is largely believed to help babies regulate their sleep-wake patterns (4).


Will eating turkey make my baby sleepier?

We wish we could answer yes to this one! Sleep is elusive for many new parents and while we are big believers that sleep is developmental, it would be nice if all we had to do was eat some turkey or other tryptophan filled food and our baby would instantly sleep better.  Despite our best wishes for an easy sleep fix, research tells us that the amount of tryptophan in our milk is based on our own natural circadian rhythm (body's internal clock) and consuming a supplement of tryptophan does not seem to make a difference in the level of tryptophan in our milk (5). But we can dream right?!

For now, our best advice is feed on demand and allow baby to load up on those higher levels of tryptophan in your milk at night. If you're a pumping mama, there is some research that suggests giving baby expressed milk at the same time of day it was originally pumped promotes the natural sleep/wake cycle due to the varying levels of components in our milk across the day (6).  Try labeling your expressed milk with the time you pump and feeding baby with milk from that time of day - so if you pump at 8pm, try giving that milk to baby at night. If you're interested in learning more about natural infant sleep and development as it relates to breastfeeding stay tuned! 



  • Human milk changes constantly to perfectly cater to our baby's needs.

  • There are a few components in our milk that are involved in helping to regulate our baby's sleep/wake cycle. One of these components is tryptophan which is involved in making serotonin and melatonin which helps regulate baby's sleep patterns and moods.

  • The level of tryptophan in human milk changes throughout the day and peaks around 3am in the morning with its lowest around 3pm in the afternoon.

  • While we cannot eat more tryptophan-filled foods like turkey to elevate our breast milk levels of tryptophan - if we are nursing on demand then our milk should be adjusting naturally throughout the day to promote sleep for our babies.

  • If you're pumping, try labeling your milk with the time of day and making sure baby is drinking around similar times to promote the natural sleep/wake cycle with our milk.



(1) National Center for Biotechnology Information. PubChem Compound Database; CID=6305. Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/6305 

(2) Lewis, T. (2013). Thanksgiving Myth Busted: Eating Turkey Won't Make You Sleepy. Retrieved from https://www.livescience.com/41543-thanksgiving-myth-busted-eating-turkey-won-t-make-you-sleepy.html

(3) Arslanoglu, S., Bertino, E., Nicocia, M. & Moro, G. (2012). Potential chronobiotic role of human milk in sleep regulation. J. Perinat. Med. 40, 1–8

(4) Cubero, J. et al. (2005). The circadian rhythm of tryptophan in breast milk affects the rhythms of 6-sulfatoxymelatonin and sleep in newborn. Neuro Endocrinol Lett., 26, 657 – 661.

(5) Dowlati, Y. et al. (2015). No effect of oral L-tryptophan or alpha-lactalbumin on total tryptophan levels in breast milk. European Neuropsychopharmacology, 25, 779–787. 

(6) Sánchez, C. et al. (2013). Evolution of the circadian profile of human milk amino acids during breastfeeding. J Appl Biomed, 11, 59-70.