Most of these use cow's milk as the protein source and have added fat, carbohydrate, vitamins and minerals. There is very little nutritional difference among them. They all come in forms containing iron, a very important mineral for infants. Many people believe iron can make a baby constipated. Actually, there is no scientific evidence for this, so you should always use an iron-containing formula to keep your child from becoming anemic.
Some infants develop a lot of gas or diarrhea while on formula.
They should be switched to a soy-protein formula such as Nursoy, ProSobee, or Isomil. These formulas are also popular among families who are strictly vegetarian. They are almost identical to one another and are not nutritionally inferior to cow's milk formulas. Powder is usually the least expensive. If you use the concentrated form, be sure you dilute it to the proper strength according to the directions on the package.