Dr. Greene’s Answer:
There are several reasons a child could develop mild diarrhea from a formula based on cow’s milk. There could be an intolerance to one of the proteins or perhaps, rarely, to the lactose. (Breast milk contains lactose so babies are very rarely lactose intolerant. That tends to develop after age 2.)
In general, soy formula results in firmer stools, and most kids who don’t tolerate cow’s milk will tolerate soy, though there are some–perhaps 20 percent–who overlap and will keep the loose stools on soy. Most of those kids do well on a hydrolysate formula, such as Nutramigen. Thankfully, most of these intolerances or allergies will get better with age. Kids who can’t take cow’s milk as an infant will usually be able to as they get older. Lactose intolerance is an exception to this–once it sets in, it often continues.
I’m in favor of formulas that have the amount of DHA and ARA recommended by the World Health Organization. Because you are nursing, your baby is getting DHA and ARA from your breast milk. You can be sure your baby is getting a rich supply if you eat one serving of salmon a week (it doesn’t take much).