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What Is the Truth About How Long Proteins Last in Your Breastmilk?

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.

Woman breastfeeding child and looking off into the distance

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. 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

Breastfeeding is not just feeding—it's a complex biological interaction. As parents, we're often concerned about what passes through breast milk to our babies, especially when allergies are involved. How much of what we eat makes its way to our children, and how long do these proteins persist in both our milk and their bodies?

Dr. Trill - molecular biologist - holding flask with breastmilk in a lab and labcoat

Despite the importance of these questions, research in this area has been limited, leaving families with more questions than answers as food allergies in infants rise. We're excited to share that Free to Feed is pioneering the first study focused on the transfer of both cow’s milk protein and soy, exploring these critical questions. You can read all about this research on our study overview and stay tuned for the peer-review publication by subscribing to our site!

Recent studies, such as the work by Zhu et al., have begun to peel back the layers of this complex issue [1]. Their research identified numerous non-human proteins in human milk, predominantly from dairy products. This groundbreaking study utilized advanced mass spectrometry techniques to detect and quantify these proteins, providing a clearer picture of how maternal diet influences breast milk composition and potential allergen exposure.

Woman eating bowl of healthy food and smiling

What this and similar studies show? All dietary proteins can and do transfer to the breast!

As we delve into common allergens like cow's milk protein, peanuts, eggs, and wheat, let's keep these insights in mind, understanding the profound impact our diet can have on our nursing journey.

Breastfeeding is a profound example of nature's efficiency, transferring not only essential nutrients like proteins, vitamins, and minerals from mother to baby, but also a complex array of dietary proteins. This transfer is a biologically normal function, designed to nurture and protect the infant. As we dive into the complexities of how specific allergens such as cow’s milk protein influence this natural process, it's important to remember that the presence of these dietary elements in breast milk is fundamentally natural. Studies, including recent advancements by Zhu et al., underscore the sophistication of breast milk and its capability to mirror the maternal diet [1]. This understanding can empower and reassure parents navigating the challenges of food sensitivities in their infants.

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 hear misinformation about dietary proteins taking weeks to leave your system. Let's dig in!

Beta Lactaglobulin in human milk chart showing clearance of protein in 6 hours
Time course of the cow's milk proteins β-Lg f(125–135) (blue line) and β-casein f(81–92) (red line) in breast milk [2].

A small study showed lactating individuals who ingested milk prior to being dairy-free, found cow’s milk protein concentration peaked at 2 hours post-ingestion and was undetectable at 6 hours [2]. Although the study was small it used a 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.” [3]

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 much longer than two weeks to completely heal as well [4].

Are you scratching your head yet? Here are some additional peer-reviewed clinical studies on this often misunderstood topic!

Some reviews have pointed to minuscule concentrations of CMP as argument against elimination diets. While we wholeheartedly do not wish an elimination of ANY food unless it is absolutely necessary, these studies have unfortunately been misleading because they are typically looking to detect the WHOLE protein within human milk. Instead, several studies have demonstrated that small fragments of CMP, rather than whole proteins, can be detected in breast milk after maternal consumption of dairy products [5].

After consuming dairy, mothers can transfer CMP fragments to their milk, which are then consumed by the breastfeeding infant. For instance, specific fragments of β-lactoglobulin (β-Lg) and αs1-casein have been identified in the milk of individuals who consume cow's milk, but these are absent in mothers on dairy-free diets [6].

Two children drinking milk and blowing bubbles in it with the straws

The presence of these peptides in breast milk does not necessarily mean they will cause an allergic reaction. In order to elicit symptoms in a child, the portion of the protein that we transfer to the breast has to match the portion of the protein that our child is reactive to [7]! This is why some families don't find out that their child has food allergies until they start solids while others of us find out through our lactation journey. It also means that some parents can continue to consume a trigger food after it has been identified through a direct trial while others cannot [8].

For parents, this information underscores the importance of monitoring both diet and infant reactions during breastfeeding, particularly if there is a family history of allergies. It's also a reminder that maternal diets need not be overly restrictive without clear medical indication. This is exactly why Free to Feed helps families conduct confirmation trials! We don't want anyone to eliminate any food long term without a clear indication that it is needed!

A 2017 study reported detectable levels of β-lactoglobulin in human milk up to 7 days after cow milk ingestion [9]. Although the findings might appear significant, the study is notably flawed due to the absence of a essential controls. This omission is critical as it prevents verification that the β-lactoglobulin detected was actually due to dietary intake rather than other variables. Furthermore, the highest concentration noted was far below the threshold known to trigger food intolerance or allergy, suggesting that the presence of this protein at such low levels may not be clinically relevant. This lack of proper controls raises significant doubts about the study's conclusions and undermines its reliability in discussing breastfeeding and food allergies.

How Long Are Peanuts Detected in Breastmilk?

The study conducted by Peter Vadas and colleagues at two North American hospitals from March 1999 to October 2000 was pivotal in establishing the scientific foundation that peanut proteins can be transferred to breast milk following maternal consumption of peanuts [10]. This research involved 23 healthy, lactating women, aged between 21 and 35 years, who participated in a controlled intake of 50 grams of dry roasted peanuts. Subsequently, breast milk samples were collected at regular hourly intervals to analyze the presence of total peanut proteins and specifically the major peanut allergens Ara h 1 and Ara h 2 [10].

Time Course of Appearance of Peanut Protein in Breast Milk
Time course of appearance of peanut protein in breast milk [10]

The findings were significant: peanut protein was detected in nearly half of the participants (11 out of 23), predominantly within the first two hours post-consumption, with one case noted at six hours. The median peak concentration of peanut protein in the breast milk was measured at 200 ng/mL, with a range from 120 to 430 ng/mL. This demonstrated not only the passage of peanut proteins into breast milk but also their substantial concentration, which could potentially expose breastfeeding infants to these allergens [10].

Further expanding our understanding, a recent study developed two sensitive and specific sandwich ELISA assays to detect the peanut allergens Ara h 2 and Ara h 6 in human breast milk. This study, conducted on a German cohort of 40 lactating women, revealed that these allergens could be detected at low nanogram levels shortly after peanut consumption. Ara h 2 was found in 35% of the participants, and Ara h 6 in 22.5%, with concentrations ranging significantly based on the time of testing post-consumption [11]. The detection of these allergens in breast milk is crucial as it provides insights into potential early exposure to allergens through breastfeeding.

Peanut proteins Ara h 2 and Ara h 6 concentrations in breast milk samples [11].
Peanut proteins Ara h 2 and Ara h 6 concentrations in breast milk samples [11].

Additional research also highlights that peanut allergens can be rapidly transferred to breast milk, with potential for preventing sensitization in infants. A study by Bernard et al. found that peanut allergens, particularly Ara h 6, were detected in breast milk as soon as 10 minutes after ingestion, with peak levels within the first hour [12]. This rapid transfer suggests that even short-term exposure to peanuts can lead to the presence of allergens in breast milk.

The study also explored the immunological activity of these allergens, demonstrating that they could bind to IgE antibodies and potentially trigger allergic reactions in vitro [12]. However, intriguingly, when these breast milk samples were administered to young mice, the exposure did not lead to sensitization. Instead, it appeared to induce a form of oral tolerance, suggesting that the presence of these allergens in breast milk, combined with other immunomodulatory components of milk, might help to protect against the development of peanut allergies in children [11].

The implications of these findings are considerable, given the rising prevalence of peanut allergies, particularly in Western countries where peanut consumption is high. The study underscored breast milk as a potential route of exposure to allergens, which might contribute to the sensitization or tolerance of infants to peanuts even before their first known direct exposure.

How Long Does Egg Last in Breastmilk?

Person cracking an egg into a bowl to be beaten

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 [13]. 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 and cleared within 8 hours of consumption [13]. This research 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.

s Mothers with egg-sensitive, eczematous breastfed infants were randomly allocated to consume one muffin per day containing one egg (egg group, n = 16) or a similar egg-free muffin (control group, n = 16) for 21 days (Days 3–23).
Mothers with egg-sensitive, eczematous breastfed infants were randomly allocated to consume one muffin per day containing one egg (egg group, n = 16) or a similar egg-free muffin (control group, n = 16) for 21 days (Days 3–23) [14].

In a fascinating trial titled "Effect of cooked and raw egg consumption on ovalbumin content of human milk: a randomized, double-blind, cross-over trial" conducted by D. J. Palmer and colleagues, breastfeeding women attended clinic days where they consumed meals with varying amounts of egg [14]. This study specifically measured the ovalbumin (OVA) concentration in breast milk and found a direct dose-response relationship between the amount of cooked egg consumed and the peak OVA concentration in breast milk. For instance, half a cooked egg resulted in significantly higher OVA levels compared to no egg at all. Additionally, OVA was detectable up to 8 hours after consumption, which challenges the notion of long-lasting protein presence [13]. Notably, the study revealed no significant difference in OVA excretion when comparing the intake of one raw egg to half a cooked egg, highlighting how the form of the egg (cooked vs. raw) impacts its detectability and concentration in breast milk [14].

The research further underscores the need for precise, controlled studies to better understand how dietary proteins like egg affect breastfeeding and infant health. This study is crucial as it helps illustrate that dietary proteins may not linger as long as previously thought, providing reassurance to breastfeeding mothers concerned about diet and allergies.

How Long is Wheat in Breastmilk?

Person's hands preparing dough

Understanding the transfer of wheat and gluten (aka gliadin) to breast milk is less researched compared to other dietary proteins. However, key studies provide insights: In one study, after consuming 20 grams of wheat, gliadin was detected in 41 out of 53 breast milk samples within 2-4 hours, highlighting that not all consumed gliadin transfers to breast milk [15].

Another study observed that after a 3-day wheat-free diet, gliadin was not detectable in breast milk samples from six participants, suggesting a rapid clearance of gliadin from the system [16]. Although the exact duration it remains detectable in breast milk remains unclear from that study, researchers believe that all dietary proteins follow very similar transfer and clearance rates [16]. These findings underscore the need for further research to clarify the mechanisms and timing of gluten transfer in lactation.

The Science On How Long Proteins Last 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. You may consume peanuts today and not see a reaction in your baby then consume them three days later and be confused when there are symptoms that time!

Two women and two children in the kitchen together

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 and groups tell families. Unfortunately, leading to more worry and confusion for parents. This misinformation can cause some parents to stop nursing because they are told that their milk is "contaminated" for weeks on end. Additionally, accidental exposures may become incredibly stressful if moms are told that any slip will cause them to "start over". If you hear claims about proteins lingering in breast milk for weeks, it's reasonable to ask for scientific evidence to back those claims. Because there aren't any peer-reviewed research studies that support that narrative.

Instead of our milk containing dietary proteins for weeks on end, what can take some time is full healing from symptoms. If you are in the midst of symptoms, we are truly sorry that you are in the trenches. Unfortunately, we know that pain all too well. According to the above research as well as working individually with thousands of Free to Feed parents, healing timing depends on how severe the reactions were to start. Once we have effectively removed the right trigger foods we should start to see some form of improvement within 5 days - enough time to clear the proteins, see the peak reactions, & begin the recovery process - and steady healing thereout until your precious little one is symptom free.

All of this gives us hope at Free to Feed and we understand the importance of continuing to breastfeed through infant food reactivity. If you want to continue breastfeeding, we’re here to help you. Understanding how long proteins last in your breastmilk is just the start of this journey and we are proud of you for being 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!

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  1. Zhu, Jing, et al. "Discovery and quantification of nonhuman proteins in human milk." Journal of proteome research 18.1 (2018): 225-238.

  2. Picariello, Gianluca, et al. "Excretion of dietary cow’s milk derived peptides into breast milk." Frontiers in Nutrition 6 (2019): 25.

  3. 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.

  4. Labrosse, Roxane, François Graham, and Jean-Christoph Caubet. "Non-IgE-mediated gastrointestinal food allergies in children: an update." Nutrients 12.7 (2020): 2086.

  5. Picariello, Gianluca, et al. "Antibody-independent identification of bovine milk-derived peptides in breast-milk." Food & function 7.8 (2016): 3402-3409.

  6. Coscia, A., et al. "Detection of cow’s milk proteins and minor components in human milk using proteomics techniques." The Journal of Maternal-Fetal & Neonatal Medicine 25.sup4 (2012): 49-51.

  7. Wal, Jean-Michel. "Bovine milk allergenicity." Annals of Allergy, Asthma & Immunology 93.5 (2004): S2-S11.

  8. Denis, M., I. Loras-Duclaux, and A. Lachaux. "Cow's milk protein allergy through human milk." Archives de pédiatrie: organe officiel de la sociéte française de pédiatrie 19.3 (2012): 305-312.

  9. Matangkasombut, Ponpan, et al. "Detection of β-lactoglobulin in human breast-milk 7 days after cow milk ingestion." Paediatrics and International Child Health 37.3 (2017): 199-203.

  10. Vadas, Peter, et al. "Detection of peanut allergens in breast milk of lactating women." Jama 285.13 (2001): 1746-1748.

  11. Schocker, Frauke, et al. "Detection of the peanut allergens Ara h 2 and Ara h 6 in human breast milk: development of 2 sensitive and specific sandwich ELISA assays." International archives of allergy and immunology 174.1 (2017): 17-25.

  12. Bernard, Herve, et al. "Peanut allergens are rapidly transferred in human breast milk and can prevent sensitization in mice." Allergy 69.7 (2014): 888-897.

  13. 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.

  14. Palmer, Debra J., Michael Steven Gold, and Maria Makrides. "Effect of cooked and raw egg consumption on ovalbumin content of human milk: a randomized, double‐blind, cross‐over trial." Clinical & Experimental Allergy 35.2 (2005): 173-178.

  15. Troncone, R., et al. "Passage of Gliadin Into Human Breast Milk." Pediatric Research 20.7 (1986): 696.

  16. 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.


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