Everywhere I look and everyone I talk to has a different opinion of when to start babies on solid foods. Most of the literature I have come across says 4-6 months, but I am starting to see more and more recommendations to wait until 6 months- and their reasoning seems very sound.
One of my favorite breastfeeding resources, kellymom.com, explains that during 4-6 months of age, a baby’s intestinal lining begins to change. When they are born, they possess an “open gut” meaning that proteins and pathogens can enter into the bloodstream. This can be a good thing for breastfed babies because it allows all of the beneficial antibodies to enter the bloodstream and help fight off potential infections. The problem happens when the baby still has an "open gut" and proteins from food enter into the bloodstream. The immune system recognizes the protein as a foreign organism and may produce an antibody to fight it off, thus making a food allergy more likely. Because there is no way to know if their gut has closed yet by outward physical signs, waiting until 6 months increases the likelihood that their gut has matured and allergy risk is (theoretically) much lower.
|Diagram from kellymom.com showing the difference between "open" and "closed" gut|