Trust your doctor (and I don't always say that!). If your son is having difficulty with absorption, he will fall below his personal growth curve. Unless your child has diarrhea (truly watery stools), I don't see any reason that you should be concerned about absorption. I'm guessing you are introducing solids slowly, as you should, in which case the majority of his diet is still breast milk. Also, one week is not very long for a baby's system to adjust. Averages for things like BMs are often not that helpful. You can have lots of kids who have one every other day and lots who have two per day and end up with an average of one per day but with few kids who actually go once a day. Obviously this is just an exaggerated example to make a point, but, even with adults, the "normal" range for frequency of bowel movements ranges from 3x per day to once every three days. Babies who are breastfed have more frequent poops than babies who are not. The one poop per day average likely includes kids who are on formula. Even if not, unless your son's poop is truly watery, you likely have nothing to worry about. My son had lots of stomach problems from quite young until he was about three, I have IBS, and I have close friends with Crohn's and ulcerative colitis. I am not one to dismiss digestive concerns. However, if your concerns are solely based on the info you have included in your post, I really do not think anything is wrong. Please do not introduce soy, as another poster suggested, because soy allergies are relatively common in children under five. From Lucile Packard Children's Hospital at Stanford's website:
"Approximately 90 percent of all food allergies are caused by the following eight foods:
The longer you wait to introduce these foods, the less likely your son will be to develop allergies to them. Most recommendations I've seen say to wait until at least 12 months for these foods (except nuts, because they're still a choking hazard at that age) and to wait longer if there is a family history of a specific food allergy. Most kids grow out of soy allergies in a few years, but why add a variable unnecessarily? The Lucile Packard website has suggestions for what types of foods to introduce next and how to do it if you're interested in more info.