CMPA in the Breastfed Baby & How Long Does Dairy Really Stay in Breastmilk?

It's not uncommon for parents to be told it takes 2-6 weeks for dairy to leave breastmilk (depending on the advice giver). This can naturally lead to some parents choosing to switch to a hypoallergenic formula, with the belief this will result in a more rapid removal of milk proteins for baby and thus relief of symptoms.

It's of course therefore that we're basing such a big decision on an evidence base, but this is actually where the problems begin.

"β-lactoglobulin (β-Lg), which is not expressed by humans, has often been monitored as a cow's milk marker. With specific concern to cow's milk allergens, exogenous β-Lg has been detected in only a limited number of mothers' milk samples, and its presence is not related to atopic or non-atopic conditions."

The search for cow's milk allergens in breast milk has been the subject of fervent research. Human and bovine β-casein, αs1-casein, and α-lactalbumin share a medium to high degree of sequence homology (53, 31, and 73% homology, respectively) and, hence, a certain immune cross-reactivity" (1)

There's a lot more info on the link I'll drop below, but in short - the protein they were tracking, doesn't appear to be linked to symptomatic babies. Symptoms didn't correlate with the appearance or removal of this, and many mothers didn't consistently show it in their milk.  Oops

Scientists of course got back on it, and identified peptides fragments - or teeny tiny bits of broken down proteins, which both appeared to correlate with consumption AND symptoms.

They found that peptides could be identified very rapidly after consumption, leaving milk quickly  with a maximum of 6 hours recorded in a 2019 study.  Authors established peptides, not proteins was a far more effective way of tracking a constituent via breastmilk and thus future studies can explore this further for other food groups.  

"Dietary peptides were already detected at 1 h (T1) after the consumption of cow's milk and peaked after 2 h, whereas none of them was detectable 6 h (T5) after the oral load." (1)

This means there is very little delay removing dairy when mum stops eating it.

This blogger and mum of a baby with allergies, who also happens to hold a Ph.D. in Cellular and Molecular Biology got digging when they were diagnosed:

"What I found was SHOCKING.
It typically takes 2-8 hours for breast milk to be clear of food allergens after ingestion.
Ingested food allergens do not always make their way to breast milk. 

Mind. Blown. Scientists have conducted several studies of breast milk at different time intervals after ingestion by the mother. For instance, one lab gave 23 women a serving of peanuts. Only half of them ended up with detectable levels of peanut protein in their milk. The milk that did contain the allergen peaked in concentration between 1-2 hours and steadily decreased from there [1].

So why didn’t my doctor tell me this?

The question emerges: WHY would doctors say it takes 2 weeks? WHY would online articles spread this lie?
I believe the answer is two-fold. First, scientific research explains that it may take up to 2 weeks for the infant to be clear of symptoms. This is the case whether the child is placed on hypoallergenic formula OR breastmilk in conjunction with an elimination diet (let’s call this hypoallergenic breast milk). So, while mothers may be clear of allergens, their infant will likely continue to show symptoms for a few more weeks."

Her blog is great, well referenced and worth a dig around if you have a baby with allergies.

Why do symptoms persist for 2 weeks if I slip up and have dairy then?

It can take up to 4 weeks for the intestinal mucosa to heal after it has been exposed to an allergen. This may be more rapid in babies receiving breastmilk due to the growth factors and pre/probiotics, anti-inflammatory constituents etc (2,3)

In practice if dairy is the issue, we see a very rapid response via breastmilk removal, which echoes the science above.

This means parents can be confident that once they stop consuming dairy, their breastmilk is rapidly clear and they can continue breastfeeding if they wish.

1. Picariello G, De Cicco M, Nocerino R, et al. Excretion of Dietary Cow's Milk Derived Peptides Into Breast Milk. Front Nutr. 2019;6:25. Published 2019 Mar 12. doi:10.3389/fnut.2019.00025
2. Brill H. Approach to milk protein allergy in infants. Can Fam Physician. 2008;54(9):1258–1264.
3. Czerwionka-Szaflarska M, Łoś-Rycharska E, Gawryjołek J. Allergic enteritis in children. Prz Gastroenterol. 2017;12(1):1–5. doi:10.5114/pg.2017.65677