Breastfeeding protects against food allergy: We have evidence

Mother breastfeeding her baby. Is she helping her child avoid food allergy?

Eating allergenic foods during pregnancy can protect your child from food allergies, especially if you breastfeed, suggests new research. The findings, in a mouse model of allergy, underscore recent advice that pregnant or nursing mothers not avoid allergenic foods like eggs and peanuts.

The study is the first controlled investigation to demonstrate protection against food allergy from breast milk, while also pointing to a biological mechanism for inducing food tolerance. It was published online today in the Journal of Experimental Medicine.

“Whether mothers should eat allergenic foods during pregnancy or avoid them has been controversial,” says Michiko Oyoshi, PhD, of Boston Children’s Division of Allergy and Immunology, who led the study in collaboration with Richard Blumberg, MD, of Brigham and Women’s Hospital, her co-senior author.

“Different studies have found different results, in part because it’s hard in human studies to know when mothers and babies first encountered a specific food,” says Oyoshi. “But in a mouse model, we can control exposure to food.”

Allergy protection from maternal antibodies

Through a series of experiments in allergy-prone mice, Oyoshi’s team showed that breastfeeding prevented food-related anaphylaxis and production of immunoglobulin E and expansion of mast cells (hallmarks of the allergic response). Specifically:

  • Pregnant mice that consumed allergenic foods such as eggs and peanuts transferred protective antibodies to their babies through their breast milk. The antibodies caused the babies to produce allergen-specific regulatory T immune cells, also known as Treg cells, which enabled them to tolerate the allergenic foods.
  • Breast milk protected against food allergy even when it was fed to unrelated offspring that hadn’t had the benefit of in utero exposure.
  • Breastfeeding was protective even when mothers had never consumed allergenic foods, but breastfed their offspring after receiving food-specific antibodies from other mothers.
  • Offspring remained free of food allergies even after the mother’s antibody disappeared from the babies’ circulation, suggesting a long-lasting effect.

Prenatal exposure and breastfeeding: A synergistic effect

Finally, Oyoshi and colleagues had mice born to allergen-exposed mothers nurse from mothers that had never consumed allergenic foods.

Mother breastfeeding in bed. Is she protecting her baby from food allergy?

“We still saw protection from the in utero exposure, but the protection was better when the mice were also exposed through breastfeeding,” says Oyoshi. “If you combine both in utero and breastfeeding exposure, you have optimal induction of food tolerance.”

Human breast milk was also protective in mice whose immune systems were tailored to respond to human antibodies, suggesting that the mouse findings may translate to human infants.

Teaching tolerance

The study also revealed the stepwise process of food tolerance, shown in this schematic. Mothers exposed to food allergens transfer antibodies to their offspring via breastmilk. Their immune systems make a complex of the antibody and allergen (the IgG-IC complex), which is transferred to nursing offspring through cells in the intestine, with the help of a receptor called FcRn.

How breast feeding protects against food allergy
Click to enlarge. (Michiko Oyoshi/Nancy Fliesler)

Dendritic cells, a type of immune cell, then process the Ig-IC complex and present it on their surface to nearby T cells. This stimulates production of Treg cells, which interact with other immune cells to suppress food allergy.

Human studies now enrolling

Do the same protective mechanisms apply to humans? Does breast milk harbor protective factors besides antibodies? To find out, Oyoshi and colleagues are now collecting milk from actively breastfeeding mothers. They will compare milk from mothers whose infants are at high versus low risk of food allergy. Risk is based on whether an older sibling is allergic, or whether the baby has early risk factors such as eczema.

“We are asking: Why is this protective mechanism not functioning in the allergic population?  Is it just lack of antibodies?” says Oyoshi, also an assistant professor at Harvard Medical School. “Maybe the mother cannot make the antibodies, or maybe something is blocking the protective pathway. We don’t really know how tolerance is induced in normal circumstances, and what causes normal tolerance to break down.”

For information on participating in the breastmilk study, phone 857-218-4729 or email

If the infant is at low risk for food allergy, the researchers will compare breast milk samples before and after the mothers eat egg or peanut. Mothers with or without a personal or family history of food allergies are eligible to enroll.

Pending the results of these studies, Oyoshi sees the possibility of treating infants at risk for food allergy with purified antibodies to those foods. In the meantime, she says, her team’s findings indicate that “you should a keep balanced diet to create antibodies to everything.”

But she adds: “Our study does not suggest that mothers’ peanut eating will guarantee a healthy baby. Given the complicated interactions between genetic and environmental factors, there is not going to be just one diet or one set of behaviors that will make children allergic or healthy.”


Asa Ohsaki in the Oyoshi lab was first author on the paper. Nicholas Venturelli, Tess M. Buccigrosso, Stavroula K. Osganian and John Lee of Boston Children’s Hospital were coauthors. The work was supported by the National Institutes of Health (#DK053056), the Harvard Digestive Diseases Center (P30DK034854), Food Allergy Research & Education (FARE), a HOPE APFED/ARTrustTM Pilot Grant, the William F. Milton Fund, the Harvard Catalyst Clinical and Translational Research Center (#8UL 1TR000170) and the Boston Children’s Hospital Pediatric Associates award.

More research from the Division of Allergy and Immunology.