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Can You Mix Breastmilk With Formula?

Can You Mix Breastmilk With Formula? (And The Best Method!)

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Many parents find themselves in a position where they need to mix breastmilk with formula, due to either supply issues or convenience. Understandably, these new mothers may also experience some concerns or guilt at the thought of having to supplement their child’s diet with formula.

Mixing breastmilk with formula (or just supplementing with it) is a perfectly normal, common, and safe method of feeding your little one. In fact, about 1/3 of all American breastfeeding mothers supplement with formula or use combination feeding by the time their baby is 6 months old.

Read on to learn more about combination feeding, nutritional concerns, and the recommended guidelines for mixing breastmilk and formula.

Is it okay to mix breastmilk with formula?

While mothers that choose to breastfeed might be upset about having to use formula, the reality is that there are many reasons why it might be necessary to supplement their breastmilk with baby formula at some point.

From a health standpoint, it is perfectly okay to alternate or even mix breastmilk with formula in the same bottle. As long as you are following all safety guidelines when preparing your formula, there should not be any concern with adding a small amount of breastmilk to the same bottle.

Nutritionally, mixing or alternating breastmilk with formula can be very beneficial for your child if they are not getting enough to eat through breastmilk alone.

Which formula is closest to breast milk?

Many formula companies are now investing significant amounts of time into developing formulas that taste as close to breastmilk as possible. While no formula can perfectly offer all of the benefits of breastmilk, some formulas come closer than others. Some of the most popular formulas that mimic breastmilk include:

Why supplement breast milk with formula

There are many reasons why parents may decide to supplement breast milk with formula. While some women are able to build up their supply by taking supplements, feeding more often or feeding on demand, there are times when it unfortunately just doesn’t work.

Sometimes, the exhaustion of constantly nursing throughout the night is simply too draining, and using formula at night can help new parents get more sleep and share the parenting duties. A mother’s body is very smart, and breastmilk supply will adjust to decrease production during the night if nursing is ceased during the overnight hours.

Supplementing breast milk with formula can make it easier for family members and other caregivers to help with feeding time and experience the same bonding moments with your baby. There is an undeniable convenience factor to being able to send a few packages of formula to daycare or grandma’s house rather than dealing with the hassle of safely transporting and storing pumped breast milk.

If your supply is just not keeping up with your baby’s needs despite your best efforts, or the thought of pumping and storing breast milk from work is just too much to handle at this point in your life, you shouldn’t feel guilty about doing what is right for your family.

What is combination feeding?

If you have ever checked into mixing formula and breastmilk then you have likely heard of something called combination feeding.

Combination feeding is simply a method of feeding your child that combines both formula and breastmilk. It has also been called mixed feeding or partial breastfeeding. Parents may feed their babies formula and breastmilk in the same bottle, or alternate between them at different feedings.

Combination feeding can be a very effective way to ensure your baby gets enough nutrition for proper development, and it is very common among breastfeeding mothers to supplement with formula.

Is breastmilk more filling than formula?

In general, breastmilk is less filling than formula – literally.

Some formulas include thickening ingredients such as maltodextrin that makes formula thicker than breastmilk. In addition, baby formula takes longer to digest. For this reason, many doctors and parents believe that feeding a baby formula at night instead of breastmilk can help them sleep longer.

However, it is important to note that this does not mean that breastmilk is less nutritious than formula. Even the best formula on the market simple cannot mimic the milk produced by the human body.

Potential issues with formula supplementation

While supplementing with formula can be helpful or even necessary for breastfeeding mothers, there are a couple of potential issues that should be noted.

Since the mother’s breastmilk supply responds to the demand of the baby through a complex process in the body, adding in formula can disrupt this equation to some degree. If your baby gets full faster or stays full longer with the formula addition, that’s less crying for breastmilk and over time that could lead to a reduced supply.

Supplementing during the early days when supply is inconsistent or low and you want to ensure that your baby has enough fluids and calories going in to increase weight is incredibly important. However, if you want to breastfeed for the long haul and ensure adequate milk supply then don’t use it as a crutch in the long-term.

As always, establishing a good relationship with a local lactation specialist can be crucial to working through the beginning stages of breastfeeding when there are sometimes more questions than answers. Discuss any issues that you are having there and formula a plan to stay on track!

Rules for mixing breastmilk and formula

If you want to mix breastmilk and formula together in the same bottle, prepare the formula on its own first, separately from the breastmilk.

Baby formulas have their own specific preparation instructions that must be followed to ensure your child’s safety. Once your baby formula has been properly prepared, it can then be added to a bottle of breastmilk.

It is important to keep in mind the following rules:

  • Follow all recommended safety guidelines for storing, mixing and preparing formula.
  • Never use breastmilk in place of water to prepare your powdered or concentrated formula.
  • Never add formula directly into breastmilk (with the exception of ready-to-feed formula).
  • Introduce formula slowly in order to help prevent further supply issues or engorgement.
  • If possible, wait until a good breastfeeding relationship is established – typically when your baby is around 6 weeks old – in order to counter any possible nipple confusion.
  • Contact your child’s doctor with any additional questions or concerns.

Can I mix breastmilk and formula and then refrigerate?

Yes, you can safely store a bottle of properly prepared breastmilk and formula for later – within reason.

Breastmilk can typically be stored in the fridge for up to 24 hours. Likewise, ready-to-use formula bottles can be stored for 1 day. Therefore, any bottles containing a mix of breastmilk and formula should be used or discarded within 24 hours of preparation.

It is also important to note that if you are accustomed to saving and reusing a bottle of room temperature breast milk for several hours, you cannot safely do this with formula. Any partially used bottle containing any amount of formula should be used or discarded within 1 hour.

Adding formula to breast milk to increase calories or weight gain

If you aren’t producing enough milk, your baby may be struggling to gain weight and reach their developmental milestones as expected. In that case, adding some formula to their diet can be a great way to increase calories and promote weight gain. Many formulas are fortified with additional nutrients like iron or DHA in order to help your child grow. Luckily, once supplementation begins, weight gain should occur fairly rapidly and your little one should be able to catch up in no time.

Some of the red flags that your baby may need a diet supplemented with formula include:

  • A loss of more than 10% body weight in the first week of life
  • Slow weight gain or even weight loss
  • Less than 6 wet diapers per day (24 hours)

As always, be sure to discuss any weight or developmental concerns with your child’s pediatrician.

Does mixing breastmilk and formula cause constipation?

While just mixing breastmilk and formula together shouldn’t cause any issues, some babies who have a milk allergy may experience an increase in digestive discomfort and other issues like constipation upon the introduction of formula.

If you do experience an increase in constipation try to cut back on the formula or try a different formula, and check with your child’s doctor. The answer may be as simple as switching to a dairy-free formula.

Alternating breastmilk and formula

Before you begin to alternate breastmilk and formula, there are some things to keep in mind. In general, you will want to wait until a good breastfeeding relationship has been established (typically around 6 weeks) and your baby is capable of accepting a bottle without experiencing nipple confusion.

There may be an adjustment period where your baby begins to reject either the breast or the bottle, and you may need to wait a bit longer before trying again if this occurs. If your baby refuses to accept a bottle at all, you can try a different bottle, a different formula, or a different caregiver to handle the feeding. Your baby might even seem to just hate formula altogether!

Many mothers practice a method known as “top off” feeding to introduce a small amount of formula to their little ones. This is done by offering baby a bottle with a small amount (around 1 ounce) of formula after a typical breastfeeding session.

Topping off with formula in this way can help your baby feel a little bit fuller, sleep a little while longer, and go a bit longer between feedings. It will also help your child get used to the different nipple associated with a bottle and the different taste of formula at a time when they are not hungry or frustrated.

Remember, any amount of breastmilk that you can produce for your baby is beneficial. Even if you are only able to supply your little one with a few ounces of breastmilk per day, they are still getting valuable antibodies and other nutritional building blocks for their growth and development.


As always, if you have any questions or concerns regarding breastfeeding, formula feeding or mixing them together, be sure to discuss them with your child’s pediatrician.

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Joshua Bartlett
Joshua Bartlett

My name is Joshua Bartlett I run this blog with my wife Jarah. We have more than 11 years of parenting experience including three girls and one boy. I started this blog in late 2018 when I realized that I was dealing with baby-related issues on a constant basis…please read more about me here!

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