One of the questions I’m asked repeatedly on my Feeding Baby Green book tour is, "What is the best timing for starting solids." My take on the best timing to start solid foods is different than what I’ve seen elsewhere. It depends on what kids are taking before that first bite of solids.
 
Breast-fed babies are already getting perfect, complex real food. Not only does breast milk provide ideal nutrient building blocks, provide ideal immune building blocks, provide an ideal closeness with Mom, and provide the greenest feeding choice imaginable, but it also provides a myriad of subtly different flavor combinations — helping to teach the baby to enjoy variety and to enjoy the foods that Mom eats. I suggest exclusive breastfeeding until babies vigorously demand solids, usually about 6 months (watching the baby for cues, not the calendar). Continuing breastfeeding in addition to solids remains valuable long after the first birthday.
 

Dr. Greene with Kelly Rutherford of Gossip Girl and Fame
at Big City Moms

Formula-fed babies, though, are getting a simple, processed food that addresses only the main nutrient needs we understand so far. I’m grateful we have them for when needed, but the babies are exposed to only one flavor profile, again and again for months on end. I suggest starting real food much earlier for these babies, when they demonstrate strong interest in what Mom is eating — usually around 4 months. This gives them complex nutrients for building blocks now and extends the window of flavor-preference learning before Neophobia (a phase of suspicion of new foods) sets in with toddlerhood.
 
Delaying or avoiding any real food beyond 4 to 6 months has never been shown to decrease allergies. Rather, I suggest avoiding the most allergenic foods when a child is taking antibiotics or when the gut is otherwise inflamed, as from illness.