There may be a good reason your child "self-limits" to these foods. Opiates, like opium, are highly addictive. If this "opiate excess" explanation applies to your child, then he is actually addicted to those foods containing the offending proteins. Although it seems as if your child will starve if you take those foods away, many parents report that after an initial "withdrawal" reaction, their children become more willing to eat other foods. After a few weeks, many children surprise their parents by further broadening their diets.