How supplementing breast milk with formula could affect your baby

After you begin supplementing breast milk with formula, you may notice some differences in your baby’s eating habits, including:


  • Refusal of breast
  • Eats faster
  • Goes longer between feedings
  • Does not pass stool after a few days

These changes are common and do not always signal a problem. But if these conditions last longer than a few days, or if you have questions about your baby's health, contact your pediatrician.


As a gentle introduction to formula, Similac® offers Similac® For Supplementation as well as a range of other formulas — hypoallergenic, soy, organic, sensitive, and more — to support your baby's unique needs, including:


  • Lactose sensitivity
  • Frequent fussiness and gas
  • Allergies and colic due to protein sensitivity
  • Frequent spit-up

We also have formulas with 2’-FL Human Milk Oligosaccharide (HMO),* a prebiotic previously only found in breast milk. Similac Pro-Advance and Similac Pro-Sensitive help strengthen your baby’s immune system to be more like a breastfed infant’s than ever before.


Similac has OptiGRO™, our exclusive blend of DHA, lutein and vitamin E. These nutrients are like those found in fish, spinach, and broccoli, respectively, and are especially helpful during the critical early stages of your baby's brain and eye development. If you need help picking or switching to the right baby formula, talk with your baby's pediatrician.


Try to prevent your baby from confusing your breast with the bottle

Your baby associates your smell with the act of breastfeeding, and might be confused if you are the one to give that first taste of formula. When your baby tries formula for the first time, it might be better if you are out of the room, or even out of the house altogether. Knowing you are around will make it more likely that your baby will hold out for breastfeeding.


Your baby can eat from a bottle faster than from your breast

Once your baby begins taking feedings from a bottle, you might be surprised at how quickly she eats. This happens because the bottle delivers milk and/or formula faster than your breast. But this is not always a sign that your baby is hungry for more. Also, be sure to try to get a burp midway through the feeding if possible, and definitely after the feeding, to relieve the pressure that can arise in your baby’s stomach from quicker eating.


Your baby can go longer between feedings without showing signs of hunger

Since formula takes longer to digest than breast milk, your baby will feel full longer, so you’ll notice him feeding less frequently. Consistent feedings are still important, though. Waiting too long could affect your baby’s health (and temperament). You can stay on top of this by keeping a record of every feeding using our printable Feeding Tracker PDF(24.3MB), or the free Similac Baby Journal app that tracks your baby’s feedings, sleep patterns, diaper changes, and more.


Your baby's stool might become firmer and develop a stronger odor

If your baby gets constipated consistently (passes stools that are hard and dry), consult your healthcare professional. Do not give over-the-counter stool softener unless advised by your healthcare professional.


What about my milk supply?

Once your baby gets used to the bottle, she might prefer it to the breast. If this happens, try breastfeeding when she is sleepy. If your milk supply is diminishing, leading to more work for less milk, pumping sessions might increase your production.



*Not from human milk.
†At significant levels.