Lately I've been hearing a lot of people saying that the advice to start solids between 4-6 months is out of date. For example, KellyMom, a usually fairly respected parenting resource says:
Health experts and breastfeeding experts agree that it’s best to wait until your baby is around six months old before offering solid foods. There has been a large amount of research on this in the recent past, and most health organizations have updated their recommendations to agree with current research.
The following organizations recommend that all babies be exclusively breastfed (no cereal, juice or any other foods) for the first 6 months of life (not the first 4-6 months)
But when a friend of mine started digging into this supposed "current research" that supports this position, she couldn't find it. So we are on the quest to find out whether there's actual research that supports this notable claim.
Even in that article, some of the sources cited do not appear to actually support the claim. For example, the article summarizes one study:
One study has shown that babies who were exclusively breastfed for 4+ months had 40% fewer ear infections than breastfed babies whose diets were supplemented with other foods.
But since that study found 4+ months was better, it doesn't support the claim that it's better to wait until 6 months.