It’s generally accepted that breast milk is best when it comes to infant nutrition, but why, exactly? We turned to registered dietitian Dana L. Kearney, MS, RD, LDN, CHC, to learn how to ensure that your choice in formula is the next best thing to breast milk.

We all know that breast milk is best, but what’s in there that makes it the gold standard? Breast milk is the perfect food for infants, and provides many benefits for your baby’s growth, health and immune system. The composition is always changing to provide exactly what your baby needs. The protein, calorie and fat content evolves as the baby’s nutritional needs change—especially during the first 6 months of life. It also contains antibodies and good bacteria to help develop baby’s immune system. Some studies even show that breast milk differs according to the gender of the child. And for moms who can’t or choose not to breastfeed (or, are supplementing), what matters most in selecting a formula? What are the key ingredients/differentiators? The type of protein used in formula is what’s really important. Protein can be tough on baby’s tiny tummy, so it is important to find a formula that breaks down the protein structure to retain its benefits, while also making it easy for baby to digest. The second factor is that babies’ nutritional needs vary dramatically as they grow—especially in the first year of a life, so formula should come in different stages tailored specifically to their development. How do babies’ specific nutritional needs change during the first months of life? A baby’s growth rate is the highest during the first month. During the second and third months, growth slows down. Solid food is typically introduced around month 6, and it’s generally low in essential fatty acids, a component that’s key to brain development. Baby’s nutritional needs again change during this transition. Many pediatricians recommend a Tri-Vi-Sol supplement for exclusively breastfed babies. How about babies who consume a combo of breast milk and formula? Exclusively formula-fed babies? When you start supplementing, you automatically receive some of these additional vitamins, as most formula is fortified. That said, always seek the advice of a pediatrician to determine if additional vitamins are needed. And, when it comes to frequency of feeding, does the schedule change depending on whether a baby is consuming breast milk versus formula? During the early weeks, a breastfed baby will most likely nurse 8 to 10 times a day for 10 to 20 minutes on each breast. Once they’ve reached a weight that the pediatrician is comfortable with, feedings can happen on an on-demand basis. For formula fed babies, after the first few days, you can generally offer a 2-3 ounce bottle every 3-4 hours (note, this is an average amount for the first few weeks). By the end of the first month, you might offer 4 ounces every 4 hours to provide about 24 ounces per 24 hour period. Not all babies consume the same amount of formula, so another useful guide is to allow 2 ½ ounces per pound of body weight for babies who have not yet started solid foods. Keeping track of daily wet diapers, monitoring growth at regular well visits, and discussing your baby’s intake with your pediatrician are all ways to help you understand if your baby is getting enough.