Dear Jean, I totally agree that sometimes the very fact that baby is on
breastmilk is what is "saving the day."  Sure it leads to delayed dx of a
problem, but the dr should be paying attention to "portal to portal" as you
say, not what is going in.  Because I believe breastmilk is practically
perfect I wouldn't even question that it was about what was "going into
baby", but what baby's body was doing with it after it gets in.
Interesting when you come at it from the other way around.  I'd be looking
for a malabsoption problem and baby would have already been to ped GI
specialist.  Sincerely, Pat in SNJ