There are a number of controversial areas in medicine when it comes to ADHD. Food allergy is certainly one of them.
The classic allergic reaction, which is classified as the type-1 hypersensitivity reaction, can be elicited by food, but this is fairly uncommon. When we discuss food sensitivities in ADHD we are discussing a different, not well-defined, mechanism.
See the full article at ADHD and Food Allergies