Do Food Allergies Contribute to ADHD, Autism and Asthma?

There is a lot of research and discussion about this topic. Delayed food allergies (IgG antibodies) can trigger allergic reactions that can cause symptoms of these disorders after a few days. What do you think? I've read in 'Flourishing with Food Allergies' and 'Healing New Childhood Epidemics' positive results.
there's a blog entry at www.flourishingwithfoodallergies.com