Supporting Breastfeeding

La Leche League Canada

Should You Mix Human Milk With Formula?

on June 13, 2016

The Canadian and American Pediatric Associations recommend exclusive breastfeeding for the first six months of life and then the slow introduction of complementary foods while continuing to breastfeed for a year or longer. Exclusive breastfeeding means nothing but breastmilk: no water, no juice and no formula. Many mothers are happy to know that their breastmilk is all baby needs in the first six months but other mothers may consider supplementing with formula for a variety of reasons. Those mothers may have questions about whether it is okay to mix formula into their breastmilk.

Dad and Babe


Here are some science based answers to this question:

It’s best not to mix breastmilk and formula in the same bottle because the storage guidelines for the two substances are very different. If you mix your milk with formula, and the baby doesn’t finish the bottle, then some of your milk goes down the drain. Formula has to be discarded after the feeding (Alberta Health) [1] whereas human milk left in the bottle can be refrigerated for another feed (LLLI Safe Handling and Storage of your milk [2]).

Mixing formula into the breastmilk will affect some of the protective components of human milk. The following quotes are from the Human Milk Banking Association of North America (HMBANA), [3] in their 2005 publication “Best Practice for Expressing, Storing and Handling Human Milk in Hospitals, Homes and Child Care Settings”: “Feed human milk, with or without fortifiers, separate from formula to maximize the benefits of human milk. If the mother is not producing sufficient milk for each feeding, collect as many pumpings as necessary to make one exclusive human milk feeding and use formula at the other feedings.”  The rationale: Quan et al [4] found that when bovine milk based formula is mixed with human milk prior to feeding, there is a significant (41-74%) decrease in lysozyme activity. Additionally, there is significant increase in the growth of E coli, resulting from the decrease in anti-infective properties in the milk. “Adding human milk fortifier causes a 19% decrease in lysozyme but no corresponding effect on the anti-infective properties or increased growth of E coli.”

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It makes sense that human milk, which is alive, would not be in its ideal state by adding a dead substance, possibly containing agents that might bind up some of the live constituents in the human milk, making them hard to absorb by the baby, or maybe not available at all.

The aim for most mothers is to exclusively human milk feed their babies. Therefore, if formula is used because the mother has not enough milk, but might in the future, it is best to treat the formula like a medicine, used temporarily and separately, to ‘top up’ her milk until such time as she has enough of her own.

Mothers with adequate milk supplies who may choose to use formula for some feedings rather than expressed breastmilk, will also want to ensure that their babies get the full benefits of the breastmilk by using the formula separately rather than mixing it with breastmilk.

If you have questions about how to increase your milk supply or any other
breastfeeding questions please contact a LLL Leader.







If you need more information or have a breastfeeding problem or concern, you are strongly encouraged to talk directly to an accredited La Leche League Leader. In Canada, Leaders can be located by clicking or Internationally

If you have found this article helpful, La Leche League Canada would appreciate your support in the form of a donation at so we can continue to help others breastfeed. Thank you!

LLLC Spring Appeal Campaign [5] for the support of breastfed babies: Help LLLC Grow – If you, or someone you know, has benefitted from the support of LLLC, a donation is one way you can “pay it forward”.
Donate Today!
Over 385,000 babies are born in Canada each year and we want to ensure every mother has access to La Leche League Canada support whenever she needs it. We are working hard to grow and we need your support. Every donation helps us provide more support to more families!
Thanks to past donations, we have been working hard to grow our services:
Our volunteer Leaders are the cornerstone of LLLC and the support we provide. We have increased our Leaders by 10% in the past year and Leader Applicants by 40% over the past 2 years!
More than 13,000 mothers attend LLLC meetings and another 20,000 receive one-to-one phone support from Leaders.
We have doubled our community and health professional outreach in just one year!
5 new Information Sheets in various languages were made available free of charge to mothers and health professionals
A new Communication Skills program was developed to strengthen health professional and breastfeeding peer support skills and our Best for Babies pre-natal program continues to grow.
Our Leaders are a vital part of LLLC’s breastfeeding foundation. They freely devote their time to help other parents give their children the optimal start in life. You, the donor, make up the other part of the foundation on which the LLLC breastfeeding services rest. Your gifts mean that our Leaders can carry out the valuable help families need. Frankly, we would be unable to deliver services to families without you or our Leaders so please take a moment to consider how valuable your support is and make a donation, either online or by using our pledge form. If a one-time donation is not suitable for you, perhaps spreading your gift over a year would make sense. Our pledge form has the monthly donation option for your convenience.
We are proud of our growth – but we want to do so much more! We need your support to help us serve even more mothers. Please donate today so we can grow to serve the mothers and babies of tomorrow.
Thank you for taking the time to consider supporting La Leche League Canada and our continued efforts to support all breastfeeding families who need us.




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