The first study^[i], a randomised controlled trial (RCT) undertaken at the University of Western Australia, showed that egg ingestion during breastfeeding was associated with increased measures of immune tolerance to eggs in the infant.

The second^[ii], a study carried out in mice at Boston Children’s Hospital, found that lactating mothers sensitised to egg protein passed antibodies on to their offspring, allowing them to tolerate the foods.

"These two new papers are significant additions to our understanding of how maternal diet affects infant egg allergy," says Dr Juliet Gray, Registered Nutritionist.

"We already know that giving eggs to babies early in the weaning process – from around 6 months - may help protect the baby against future egg allergy, but there has been little information on the effect of breastfeeding on allergenic potential later in childhood.

"These new studies both showed that eating eggs when breastfeeding may influence the development of infant oral tolerance to eggs."

The first study investigated how maternal dietary egg ingestion during early breastfeeding influences egg protein (ovalbumin) levels detected in human breastmilk and whether this influences sensitivity or tolerance to egg protein in the infant.

Women were allocated to a dietary group for the first six weeks of lactation: high-egg diet (> 4 eggs per week), low-egg diet (one-three eggs per week) or an egg-free diet. Breastmilk samples were collected at 2, 4 and 6 weeks of lactation for the measurement of ovalbumin.

Blood levels of egg-specific immunoglobulin E (a measure of sensitisation to egg) and immunoglobulin G4 (IgG4) (an indication of protection against allergy and tolerance to egg) were measured in the infants at 6 weeks as well as before introducing egg in solids at 16 weeks.

Average maternal egg ingestion correlated with breastmilk ovalbumin concentration; for each additional egg ingested each week, there was an average 25 per cent increase in ovalbumin concentration.

Ovalbumin concentrations were significantly higher in the breastmilk of the 'high-egg' group compared with the 'egg-free' group. Blood levels of egg-specific IgG4 in the infants were positively related to maternal egg consumption, with an average 22 per cent increase in infant egg-specific IgG4 per additional egg consumed each week.

The researchers concluded that increased maternal egg consumption is associated with increased breastmilk ovalbumin, and with markers of immune tolerance in infants. These results highlight the potential for maternal diet to benefit the development of oral tolerance in the infant during lactation.

The second study, published this month in the Journal of Experimental Medicine, was a controlled investigation to demonstrate protection against food allergy by breastmilk.

Through a series of experiments in a mouse model which had similar features to human food allergy, the research team showed that pregnant and breastfeeding mice exposed through the skin barrier to ovalbumin (egg protein) transferred protective antibodies to their babies through their breastmilk.

The antibodies caused the babies to produce allergen-specific regulatory T immune cells, also known as Treg cells, which appears to have enabled them to tolerate the allergenic food. The babies from sensitised mothers who were then subjected to skin sensitisation and oral challenge to ovalbumin showed a much smaller allergic response to the allergen.

Breastmilk appeared to protect against food allergy even when it was fed to unrelated offspring whom had not experienced in utero exposure to maternal antibodies. Furthermore, when mothers had not been sensitised, but were supplemented with ovalbumin-specific antibodies whilst breastfeeding, the babies were also protected.

Even after the mother’s antibody disappeared from the babies’ circulation, they showed no allergic response to skin or oral challenges with ovalbumin, suggesting a long-lasting effect.

The researchers also examined mice born to allergen-exposed mothers nursed from mothers that had never consumed allergenic foods.

"We still saw protection from the in utero exposure, but the protection was better when the mice were also exposed through breastfeeding," says Michiko Oyoshi, PhD, of Boston Children’s Division of Allergy and Immunology, who led the study

"If you combine both in utero and breastfeeding exposure, you have optimal induction of food tolerance.

"It’s hard in human studies to know when mothers and babies first encountered a specific food.

"But in a mouse model, we can control exposure to food."

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.

[i] Metcalf et al. (2016)
Clin Exp Allergy. (link is external) 2016 Dec;46(12):1605-1613. doi: 10.1111/cea.12806. Epub 2016 Oct 7.
[ii] Ohsaki et al. (2017) doi: 10.1084/jem.20171163 http://jem.rupress.org/content/early/2017/11/17/jem.20171163