Detection of bovine milk–, but likely not soy–derived, peptides in human milk after maternal consumption of bovine milk and soy beverage: a randomized, cross-over, dietary intervention trial
When a breastfeeding mother eats dairy or drinks soy milk, do proteins from those foods show up in her breast milk? And if she stops eating them, how long does it take for those proteins to disappear?
College of Health researcher(s)
College unit(s)
Abstract
Background
Food-borne allergens in human milk (HM) may cause allergic responses in HM-fed infants, but variability of allergen transfer complicates recommendations for individuals nursing food-allergic infants.
Objective
We aimed to identify bovine- and soy-derived peptides in HM after maternal elimination and reintroduction of bovine milk (BM) and soy beverage (SB).
Methods
In this randomized, cross-over, dietary intervention trial, 38 lactating participants underwent 2 study phases, each including a 5-day diet elimination, 3-day diet intervention, and 2-day washout. Each diet intervention required daily consumption of increasing amounts of BM or SB (175, 295, and 415 mL). Peptidomics analysis was performed on a subset of HM samples (24 participants) collected after dietary elimination, and 2 and 4 h after BM/SB consumption (415 mL). Peptides were isolated via ethanol precipitation and C18 solid-phase extraction, analyzed by LC–MS/MS, and identified with Proteome Discoverer.
Results
We identified 121 bovine-derived peptides (associated with 6 proteins) in HM collected during the BM phase. From most to least abundant, these proteins were β-lactoglobulin, κ-casein, αs1-casein, β-casein, α-lactalbumin protein variant D, and glycosylation-dependent cell adhesion molecule 1. Generalized linear mixed models demonstrated differences in relative abundance for 14 peptides when comparing before, and 2 and 4 h after BM consumption. We identified 8 peptides of possible soy origin in HM collected during the SB phase, but they were not matched to parent proteins with adequate confidence.
Conclusion
The relative abundance of some BM-derived peptides, while low overall, may differ in human milk collected after maternal BM dietary elimination compared to 2 and 4 h after BM consumption. Five days of dietary elimination may not be adequate for the elimination of BM-derived peptides or low levels of these non-human peptides may be present in HM from other sources. No confident soy-derived peptides from the SB were identified in HM after consumption.
Cow's Milk and Soy in Breast Milk: An FAQ on the Latest Research
What was the main goal of this study?
The core issue this study addressed is that food allergens consumed by a nursing mother can enter her breast milk and potentially trigger allergic reactions in her baby.
The primary objective was to use highly sensitive and rigorous methods to determine if peptides—small fragments of proteins—from cow's milk and a soy beverage could be detected in human milk. The researchers tested this by having participants first eliminate these foods from their diet and then systematically reintroduce them while providing milk samples for analysis.
Can food allergens from a mother's diet really pass into her breast milk?
Yes. Research has demonstrated that various allergens from a mother's diet can be transferred into her milk. Specifically, proteins and peptides from foods like bovine milk (cow's milk), eggs, and peanuts have been shown to appear in human milk after maternal consumption.
Critically, the presence and concentration of these allergens are known to be highly variable. This variation occurs not only between different individuals but also within the same person at different times, which makes it challenging to create universal recommendations for nursing parents of food-allergic infants.
What did the study find about cow's milk proteins in breast milk?
The researchers successfully identified 121 unique bovine-derived peptides in the human milk samples they analyzed. These peptides were fragments of larger cow's milk proteins.
The six parent proteins these peptides were associated with, listed from most to least abundant in the study, were:
- β-lactoglobulin
- κ-casein
- αs1-casein
- β-casein
- α-lactalbumin protein variant D
- glycosylation-dependent cell adhesion molecule 1
While these protein fragments were clearly detectable with advanced methods, the study concluded that their overall relative abundance in the milk samples was low. This finding of low abundance is important, as it directly relates to the risk of triggering an allergic reaction.
How long do cow's milk proteins stay in breast milk after a mother stops consuming dairy?
In an unexpected finding, the study identified bovine-derived peptides in all human milk samples, including those collected after the mothers had completed a 5-day dietary elimination period for cow's milk. This was surprising because some previous, smaller-scale research had suggested these peptides might clear from milk in a matter of hours. This study's use of more sensitive methods suggests the process may be more complex.
This result suggests two main possibilities:
- A 5-day elimination period may not be long enough to completely clear all bovine peptides from human milk.
- Alternatively, very low levels of these non-human peptides may be persistently present due to factors like unintentional dietary exposure to trace amounts of bovine peptides in processed foods, or environmental exposure, such as when other household members continue to consume dairy products in the home.
Are the detected amounts of cow's milk peptides enough to harm an allergic infant?
While the study measured the relative abundance of peptides rather than their absolute quantities, the levels found were consistently very low.
Based on these findings, the study concluded that the low abundance of these peptides is likely below the threshold needed to trigger an allergic reaction in over 99% of infants with an IgE-mediated cow's milk allergy (CMA). It is important to note that this estimate is based on IgE-mediated allergies, and the study did not directly measure clinical reactions in infants. While these findings are reassuring, they do not account for other mechanisms, such as non-IgE-mediated reactions.
What did the study find about soy in breast milk?
The study did not confidently identify any soy-derived peptides in human milk after mothers consumed a soy beverage.
Although the initial analysis found 8 peptides of "possible soy origin," the researchers could not match them to soy parent proteins with adequate confidence to confirm they came from the soy beverage.
Why was it difficult to confirm the presence of soy peptides?
The inconclusive findings for soy were due to two significant analytical challenges:
- High Similarity to Other Foods: Several of the potential soy peptides shared a high degree of similarity with proteins from other sources, including other plants and common foods like potatoes and peas. This made it difficult to be certain that the peptides originated from soy.
- Absence in the Source Beverage: This was the key piece of evidence. When the researchers directly analyzed the soy beverage that participants consumed, they found that none of the 8 potential soy peptides detected in the human milk samples were actually present in the beverage itself. If the peptides found in the breast milk weren't in the soy beverage the mothers drank, it's almost certain they came from another source.
In simple terms, how was this research conducted?
The study was designed as a randomized, cross-over dietary intervention trial, which is a robust way to test the effects of a specific diet. The process for each of the lactating participants involved a sequence of clear steps:
- Step 1: Elimination and Reintroduction: Participants eliminated either cow's milk or soy from their diet for 5 days. Then, over the next 3 days, they consumed increasing amounts of that specific beverage while providing milk samples for analysis.
- Step 2: A Rest and Reset Period: Participants took a 2-day break, during which they continued to avoid the test food.
- Step 3: The Crossover: The entire process was repeated with the other beverage. For example, if a participant had cow's milk in Step 1, they would have the soy beverage in this step.
This design allowed each participant to serve as her own control, strengthening the study's conclusions.
What made this study's methods particularly powerful?
This research stood out because of its rigorous and highly sensitive methodology. The key strengths included:
- Advanced Technology: The study used a technique called liquid chromatography–tandem mass spectrometry (LC-MS/MS). This method is exceptionally powerful because it can detect very small protein fragments (peptides) at extremely low concentrations that might be missed by less sensitive techniques.
- Reliable Design: The crossover design, where every participant acted as their own control, reduces the influence of individual differences and makes the results more powerful.
What is the main takeaway for parents and researchers?
The study's primary conclusions can be synthesized into three key points:
- Cow's Milk: Peptides from cow's milk are present in human milk after maternal consumption, but in very low amounts.
- Persistence vs. Risk: These peptides can persist even after a 5-day elimination diet. However, their levels are likely too low to cause an allergic reaction in the vast majority of infants with a cow's milk allergy.
- Soy: Using highly sensitive methods, peptides from the consumed soy beverage could not be confidently detected in human milk.
The study highlights the need for future research to better understand the individual variability in allergen transfer, the timing of clearance from milk, and, most importantly, to confirm what these trace amounts mean for managing an infant's symptoms and allergies in the real world.