Another good post from News Moms Need (March of Dimes). I'm reprinting here:

Medical research on the prevention of food allergies unfortunately is limited and incomplete. After reviewing a wide range of medical research, the American Academy of Pediatrics has made these recommendations about food allergies in children:

• Avoiding certain foods in pregnancy does not appear to prevent food allergies in children.
• We don’t know for certain if breastfeeding can prevent or delay food allergies. For infants who have a parent, brother or sister with a food allergy, drinking only breast milk for at least four months may reduce the risk of allergy to cow’s milk. Certain formulas that do not contain cow’s milk may also reduce the risk.
• Soy-based infant formula does not appear to prevent food allergy.
• Doctors recommend that most babies start eating solid foods between 4-6 months of age. Some people have thought that food allergies might be prevented if parents delayed giving their babies certain solid foods (for instance, fish, eggs, peanut butter). But current research doesn’t support this idea.

Thankfully, food allergies are often outgrown during early childhood. Approximately 80% to 90% of egg, milk, wheat, and soy allergies are gone by age 5 years. Some allergies are tougher and last longer, so you need to be certain they are gone before reintroducing the food to a child’s diet. For example, AAP says 1 in 5 young children will outgrow a peanut allergy and fewer will outgrow allergies to nuts or seafood. Your pediatrician or allergist can perform tests to track your child’s food allergies and watch to see if they are going away.

Medical research about food allergies is continuing and we’ll give you updates when we learn more. If you have any questions about food and your baby, ask your child’s health care provider.