All infant formulas are designed to replace breast milk as the sole form of nutrition during a baby's first few months of life. According to the Mayo Clinic, all formulas must meet the same government standards in terms of nutrients, but soy and regular cows' milk based formulas have different ingredients. Soy formulas are often marketed as an alternative for babies who are allergic to cows' milk based formulas or whose parents are vegan.
Regular formulas are based on cows' milk. Soy formulas are based on soy milk. According to pediatrician and author Dr. William Sears, who compiled a list of common formula ingredients, regular cows' milk formulas contain nonfat milk and whey protein concentrate, in the form of 60% whey and 40% casein. The protein in soy formula is soy protein isolate.
The fats in both regular and soy formula are the same. Dr. Sears states that all formulas contain a blend of palm oil, high oleic (safflower or sunflower) oil, coconut oil and soybean oil as sources of fat. Like human milk, all formula must contain fat to aid in brain development.
Formulas contain carbohydrates, which gives the formula a moderately sweet taste. The carbohydrate in regular cow's milk formula comes from naturally occurring lactose. Because carbohydrates are not naturally present in soy, corn syrup solids and sucrose are added.
The most common reason for choosing to feed soy formula is that the baby displays symptoms of allergy to cow's milk formulas. Pediatricians will often recommend this after trying several brands of cow's milk formula. Soy formula does not necessarily resolve food allergy issues because many people who are allergic to cow's milk are also allergic to soy and corn, which is also present in soy formulas that contain corn syrup.
Vegans are people who do not consume any animal products, including meat, dairy, honey or gelatin. Because cow's milk formulas contain dairy and soy formulas do not, some vegan parents prefer to feed their babies soy formula. According to the Vegetarian Resource Group, vegan parents who are extremely concerned about avoiding animal products should read the ingredient labels on soy formula carefully, as some may contain animal-derived fats.
The American Academy of Pediatrics (AAP) cautions against giving soy formula to preterm infants. The AAP also says that switching to soy formula is not an appropriate way to attempt to manage colic, even though many people try it for this purpose. Furthermore, a study by the Arkansas Children's Nutrition Center suggested that soy formula may alter drug metabolism later in life and expressed concern about the fact that no one consumes more soy for their body weight than infants fed soy formula.