You’re told your baby may have a protein intolerance or allergy. You need to change your diet to continue breast or body feeding. You feel like you’ll do whatever you have to do for the health of your baby.
Then you’re told it may take up to two weeks for food proteins to clear out of your system. And then two more weeks to clear out of your baby’s system.
Something is wrong with your baby and you’re concerned. And now you have to wait a month for hopes of improvement. Even worse, some groups state that it can take up to 8 weeks!?
The timing doesn’t seem to add up and many professionals don’t seem confident in their answers either.
So...here you are reading every label and hoping that your breast milk isn’t harming your baby.
Here at Free to Feed our mission is to provide scientific evidence and help parents reach their feeding goals through food reactivity.
Here are some facts backed by science on how long food proteins remain in human milk.
Food Proteins Do Transfer into Breast Milk
We know a nursing parent's diet is important while breastfeeding. We also know what we consumes goes to the baby. When you’re told you need to change your diet, you have lots of questions.
How much is getting to the baby?
How long do proteins stay in my breastmilk?
How long are the proteins in my baby’s system?
It’s impossible to answer these questions definitively. There is still a great need for more research on protein transfer and breast milk studies. We know the medical field is lacking in this research as the number of infant food allergies and intolerances continues to grow.
We’re happy to say Free to Feed is currently holding the first study looking at both cow’s milk protein and soy transfer!
It’s hard to place a value on breastmilk. Some refer to it as liquid gold. Even the best formula cannot replicate what human milk gives to infants (when it is an option).
But if your baby has allergies, it’s easy for the medical field to push formula to solve the problem. This can be stressful for families that wish to breast or body feed.
Let’s take a look at some common food allergens including cow’s milk protein, peanuts, egg, and wheat.
How Long Does Dairy Last In Breast Milk?
Cow’s milk protein allergy (CMPA) is the most common source of reactivity for infants. If your baby is suspected to have a food allergy, it’s likely recommended to stop all cow’s milk protein (all forms of dairy products) first. This is where you’ll likely get answers about it taking weeks to leave your system.
A small study showed lactating individuals who ingested milk prior to being dairy-free, found cow’s milk protein peaked at 2 hours post-ingestion and was undetectable at 6 hours . Although the study was small it was using mass spectrometer ion intensity testing which is incredibly accurate.
Let that sink in for a moment... Undetectable at 6 hours!
Also, the Journal of Pediatric Gastroenterology and Nutrition reports “for an immediate reaction the maternal elimination diet needs to be maintained for only 3 to 6 days. If delayed reactions are suspected (such as allergic proctocolitis which can cause bloody stool), then the diet should be continued for up to 14 days. If there is no improvement, then it is likely that diagnoses other than CMPA are the cause of the symptoms and the child should be further evaluated.” 
If we take a step back and think about this we can learn and understand from these studies. If cow’s milk protein was still present in human milk weeks after consumption, then acute reactions - those which happen within hours of exposure and heal quickly - would continue past a few days. Chronic reactions - those responses which take longer to occur (often within 6-48 hours) and longer to heal because they essentially cause a wound - would take longer than two weeks to resolve as well.
Are you scratching your head yet?
How Long Are Peanuts Detected in Breastmilk?
Most of us are aware that peanuts have been a growing allergic concern for children and adults. Remember when they used to hand out peanuts on airplanes? You won’t see that often due to the increase in peanut allergies among the population.
But how long are they in breastmilk?
A study conducted in Toronto showed that of 23 lactating participants, only 11 showed peanuts in their breast milk after consumption. Peak levels were noted at 1-2 hours after ingesting 50 grams of peanuts. 
In 10 of the 11 people, peanut proteins were undetectable after 8 hours of consuming peanuts. 
Let me repeat that, undetectable after 8 hours.
Although this is only one study, it’s fascinating that in some, the peanut protein was never detected in their breast milk. There is likely a multitude of factors contributing to this. However, we can learn that not all proteins will transfer to your milk every time.
How Long Does Egg Last in Breastmilk?
Scientists have found that daily consumption of egg did not result in the accumulation of egg protein in breast milk over time in a study where lactating participants were given a daily muffin containing egg. 
We’re often told the more we consume something the more it “builds up” in our system, thus the longer it takes to clear out. The egg study shows us this isn’t the case.
The same study also found that egg concentration peaked within 8 hours of consumption.  This study also provided more information on how food being cooked can alter the protein concentration. So there is a clear difference between eating a muffin versus a plain egg.
How Long is Wheat in Breastmilk?
There is a specific protein in wheat called gliadin which is also known as gluten. A study was conducted showing that 53 lactating participants consumed 20 grams of wheat and only 41 tested positive for gliadin . This again shows us not all proteins will transfer to breast milk with consumption.
Another study showed 6 individuals who were put on a 3-day wheat-free diet and their breastmilk did not detect gliadin.  This could mean wheat cleared of their system much sooner than 3 days, but it definitely didn’t take two weeks!
The Science On How Long Food Proteins Are In Your Breastmilk
There are important key points that we want you to take with you from reading this. First, not all ingested proteins enter into human milk (the peanut and wheat example). Second, when proteins were detected they cleared reactivity-inducing concentrations within 24 hours, often much sooner within 6-8 hours. Research indicates that this is the case across all dietary proteins we consume. This makes sense because it matches what we know about other molecule transfer such as flavonoids and alcohol.
This goes against what many professionals tell families. Unfortunately, leading to more worry and confusion for parents. This can cause some parents to stop nursing because their milk will “poison” their baby for weeks on end and accidental exposures are incredibly stressful. If anyone tells you that protein stays in your milk for weeks, ask them for their scientific sources. Because there aren't any that support that narrative.
All of this gives us hope at Free to Feed and we understand the importance of continuing to breastfeed through infant allergies and intolerances. If you want to continue breastfeeding, we’re here to help you.
For more scientific data we have found and to learn more, visit here.
If you're suffering trying to find what's causing your baby's reaction, consider a one-on-one consult for resources and support!
Picariello, Gianluca, et al. "Excretion of dietary cow’s milk derived peptides into breast milk." Frontiers in Nutrition 6 (2019): 25.
Koletzko, S., et al. "Diagnostic approach and management of cow's-milk protein allergy in infants and children: ESPGHAN GI Committee practical guidelines." Journal of pediatric gastroenterology and nutrition 55.2 (2012): 221-229.
Vadas, Peter, et al. "Detection of peanut allergens in breast milk of lactating women." Jama 285.13 (2001): 1746-1748.
Palmer, D. J., M. S. Gold, and M. Makrides. "Effect of maternal egg consumption on breast milk ovalbumin concentration." Clinical & Experimental Allergy 38.7 (2008): 1186-1191.
Troncone, R., et al. "Passage of Gliadin Into Human Breast Milk." Pediatric Research 20.7 (1986): 696.
Chirdo, F. G., et al. "Presence of high levels of non-degraded gliadin in breast milk from healthy mothers." Scandinavian journal of gastroenterology 33.11 (1998): 1186-1192.