Can You Mix Breast Milk & Formula?

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Breast milk is the best nutrition your baby needs for growth and development. It’s packed with vitamins, minerals, and even antibodies. These antibodies provide your newborn’s intestinal tract with its first source of adaptive immunity to help prevent illnesses. (1)

You can opt to pump and store your breast milk if you need to be away from your baby.

Infant formula is the next best choice if you aren’t able or choose not to breastfeed. Formula is meant to mimic breast milk’s nutritional composition closely.

But you might be wondering whether you can mix pumped breast milk and formula.

Is it safe to mix the two? What possible side effects might your baby experience? Can it lead to medical issues?

Many parents are scared and confused given the recent major formula recalls and formula shortages. Apparently, formula can also cause illnesses, even death.

Angry parents have also filed an Enfamil and Similac baby formula lawsuit after some studies showed that their products might cause NEC (Necrotizing Enterocolitis). (2)

NEC is a serious gastrointestinal condition that can cause inflammation and death of intestinal tissues. If that happens, waste and bacteria can pass into your baby’s bloodstream. (3)

In a 2012 study, the digested forms of the following infant formulas led to the death of intestinal cells in vitro: (2)

  • Enfamil Infant
  • Enfamil Premature
  • Enfamil EnfaCare
  • Similac Advance
  • Similac Soy
  • Similac Special Care
  • Similac Expert Care NeoSure


Fresh human breast milk didn’t lead to the same results. (2)

The lawsuit alleges that baby formula makers should have known about the potentially harmful effects of their products and informed consumers of the risks. However, none of their products contain a warning label.

Is It Alright To Mix Breast Milk & Formula?

Yes. You can mix breast milk and formula.

Combining the two doesn’t appear to be dangerous as long as the breast milk was pumped and stored hygienically and the formula was stored properly.

Also, be sure to check for baby formula recalls regularly, so you won’t accidentally give your baby a contaminated formula.

However, you should also be aware of the risks of using baby formula and mixing it with breast milk.

Why Should You Not Mix Breast Milk With Formula?

Mother Nature provides you with breast milk for free, and it’s considered liquid gold.

If you directly mix breast milk with formula, you risk wasting your liquid gold if your baby doesn’t consume the entire bottle. Remember that you need to discard the contents of an unfinished bottle because it can easily become a breeding ground for bacteria. (4)

What’s The Best Way To Mix Breast Milk & Formula?

Instead of mixing the two, it’s better to prioritize feeding your baby breast milk (pumped milk in a bottle will do), then supplement with a formula bottle if necessary.

Mixed feeding is the combination of breastfeeding and formula feeding within the same period.

The AAP (American Academy of Pediatrics) recommends exclusive breastfeeding for your baby’s first six months of life. They also recommend continued breastfeeding for one year or longer while providing your baby with nutritious foods. (5)

However, this isn’t really practiced in reality.

Studies show that as much as 23% to 32% of babies are provided nourishment through mixed feeding.

A 2011 study in The Journal of Pediatrics showed that mixed feeding could lead to an increased risk for obesity between ages 2 and 6 years than four months of exclusive breastfeeding. (6)

Mixed feeding is also associated with shorter overall breastfeeding duration. (6)

Effects Of Mixing Breast Milk & Formula

Reduced Breast Milk Supply

Regular mixed feedings can reduce your breast milk supply because it tricks your body into thinking that your baby no longer needs a lot of milk.

Potential Interactions

Although it tries to mimic breast milk as closely as possible, some formulas these days contain special ingredients or might have a different composition of fat blends, carbohydrates, and other nutrients. (7)

These ingredients can lead to potential interactions that could affect your little one.

Can Mixing Formula & Breast Milk Cause Upset Stomach?

The combination might not be dangerous but it could upset your baby’s tummy.

Studies show that your baby’s intestinal microbiome can vary depending on what they eat. So, an exclusively breastfed baby has different gut bacteria than a formula-fed one. (8)

Surprisingly, the gut bacteria communities of mixed-fed babies were more similar to exclusively formula-fed infants than exclusively breastfed ones. (8)

Does Mixing Breast Milk & Formula Cause Constipation?

It’s fairly common for babies to experience constipation when they first start using formula. So, giving them a mix of breast milk and formula might trigger a similar effect.

Exposure To Contaminated Formula

Giving formula can increase your baby’s risk of exposure to contaminated formula.

For example, at least nine infant deaths were reportedly linked to recalled Abbott Nutrition (Similac) formulas. (9)

Infant Formulas & NEC

Formula-fed premature babies have an increased risk for NEC (necrotizing enterocolitis). (3)












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