The Link Between Breastfeeding and Allergies

As a new mom who’s breastfeeding, you’ve probably heard the old adage, “your baby eats what you eat.” But is this really true? And what does it mean for allergenic foods like peanut butter? Read on to learn more about the connection between breastfeeding and allergies. 

What Is In Breast Milk?

Breast milk is made in the breast tissue when your body takes protein, fat, water, and sugar from your blood supply and turns them into breast milk. Colostrum, the thick milk made in the first couple of days after birth, early milk made by your breasts, is made mostly of protein and immune cells (antibodies). Regular breast milk is mostly water to keep your baby hydrated, and fat and sugar to gain weight. 

Breast milk is not directly made of what you eat. 

When you eat Cheetos or kale, your breast milk does not have Cheetos or kale in it. Your body will take the sugar, protein, fat, and water from your food and turn it into breast milk.

Breast Milk Passes Immune Cells to a Baby

While you’re not exactly passing the same food you’re eating to your baby through breast milk, you are passing important immune cells to your baby, because they are in your blood. 

When a baby is first born, they cannot make their own immune cells or fight off bacteria and viruses. Babies get their first immune cells, like antibodies, from their mother’s breast milk. 

Some immune cells a mother gives to her baby help the baby’s body learn to fight off viruses. Other immune cells from mom actually teach a baby’s immune system when to stay calm and not react. Together, these immune cells help a baby find balance between recognizing threats and acting normal.

Breastfeeding for even the first 2 to 3 days of your baby’s life can give your baby most of their immune starter-kit from the colostrum. Breastfeeding for two months will keep adding new antibodies until a baby is more capable of making their own immune cells.

Breast is Best for the Early Microbiome

Breast milk also helps babies develop the right gut microbiome, which also plays a role in a healthy immune system. Breast milk turns the sugar in your body into special sugars called complex oligosaccharides. While infant formula does contain all the nutrition a baby needs, only breastmilk has these special sugars. 

There is a bacteria called B. infantis that eats breast milk sugars and turns them into the mucus that strengthens a baby’s stomach and intestines. Babies cannot make this mucus on their own, and B infantis can only get their sugars from breast milk!

After a baby starts solid foods, their microbiome changes dramatically. Breastfeeding until the start of solids will make sure that the early microbiome gets the food it needs.

Is Your Baby Reacting to Breast Milk ?

While breast milk is mostly water, fat, and sugar, it does contain some protein. Babies cannot react to water, fat, or sugar, but they can react to proteins in breast milk.

How much protein is in breast milk differs from mother to mother. For example it has been shown that in about 40% of women, peanut proteins were detectable in the expressed breast milk one to two hours after peanut consumption. 

Some doctors now think that mothers with leaky guts are more likely to have undigested food protein in their bloodstream and therefore more likely to pass that protein through their breast milk. So, it is possible that proteins from food make it directly into breast milk. 

For a baby to react to proteins in breastmilk, undigested food proteins need to be in a mother’s milk, and the baby has to have developed antibodies to those proteins. This is somewhat rare but it does happen. 

A reaction to breast milk can appear as:

  • Eczema or dry, red skin
  • Belly pain
  • Constipation
  • Runny poops, or blood poops
  • Reflux
  • Excessive crying

Teething, viruses, and other things can cause these same symptoms, but symptoms that last for more than a week or worsen should not be ignored or brushed aside. Your pediatrician may suggest an elimination diet or switching to hypoallergenic formula to see it clears the symptoms. 

If your baby is reacting to a protein in breast milk, eliminating it from your diet for as little as 1 day will clear it from your breast milk. However, the symptoms can last for up to two weeks.  Check out the resources at to learn more.

Breastfeeding Cannot Not Train Food Tolerance

Although breastfeeding does support a healthy immune system and healthy gut microbiome, studies comparing food allergy rates in breastfed and formula fed infants shows no difference. 

Studies dating back to the 1970’s all the way through today show that there isn’t a difference in allergy rates between children who are breastfed, given cow’s milk formula, or soy formula.

On the other hand, daily supplementation with an ounce of formula has been proven to prevent cow’s milk allergy.

Why? As we discussed above, most mothers’ breastmilk does not contain much if any food proteins, only water fat and sugar. When drinking breast milk, most babies are not getting very much or any exposure to the actual foods. They are not getting any training to tolerate those foods.

Eating allergenic foods, or not, while pregnant or nursing probably has little effect on allergy rates, unless your child is showing signs of reacting to breast milk. Whether a child reacts to breast milk or not, only early allergen introduction, once a baby can start solid food, can train a baby’s immune system to tolerate proteins like peanut, egg, and more.