When it comes to infant nutrition, breast milk is always the gold standard. So when you supplement or rely exclusively on formula, the decision can be emotional—and the options overwhelming. We turned to pediatric nutritionist Nicole Silber, RD, CSP to get a better understanding of what matters when selecting infant formula.

First thing’s first—what’s actually in formula? Formula aims to mimic breast milk through a combination of proteins, fats, and carbohydrates. While the immune benefits of breast milk can’t be replicated, almost everything else can. Why organic? The milk protein used in organic formula comes from farmers who have higher standards of how they raise their animals.  It also means that the milk is free of hormones and antibiotics. Sounds like the right place to start. What else varies among different brands? All standard (cow’s milk-based) formulas contain fat in the form of a blend that includes sunflower, soybean, safflower, and/or coconut oils. The carb component is derived from a combination of lactose and/or brown rice syrup and corn syrup solid. Whey and casein make up the protein piece of the puzzle. Earth’s Best Organic Infant Formula has a whey/casein mix that closely matches breast milk’s composition. What ingredients should parents look for on formula labels? Look first at the protein source. Unless there’s an allergy or specific sensitivity, a milk-based formula is a good place to start. You want one with more whey than casein, and it should contain lactose, too. It’s also important to look for DHA and ARA fortification, which helps brain and eye development. And how do you introduce formula to a breastfed baby? Breast milk and formula are absorbed differently, so a gradual ease-in is best. Nicole recommends mixing a bottle with 1/4 formula and 3/4 breast milk, then transitioning over a 10 day period. If they spit up, is that a sign that the formula isn’t agreeing with them? No. Babies’ stomachs are immature, and it takes some time to regulate. Spit up and changes in the baby’s poop consistency are normal. Formula isn’t as easy to digest, so some spit up is definitely normal, especially in the beginning. Hard stool and projectile vomiting are signs that something is wrong. Should different formula be used at different developmental stages? Generally speaking, no. Infant formula should cover babies up through age 1 (again, that immature stomach thing means that the less change, the better). And remember, the FDA and USDA regulation on formula is strict. To be called “infant formula,” it has to be a complete product, containing all the calories, protein, fat, and essential vitamins and minerals a baby needs.