Please be aware that natural food chemicals (amines, glutamates & salicylates) in 'healthy' food like fruit, vegetables, browned meat, etc can also affect behaviour in the same way that artificial food chemicals do. Typical offenders are really common foods like bananas, corn, zucchini, cheese, tomatoes etc. Probably the only way you will find out is by reading up on resources like Sue Dengate's website and book, and doing an elimination diet and then reintroducing foods until you work out what's setting him off.

Oh, and the food chemicals have a cumulative effect too. So while eating a banana one day might be ok, if they also have a tomato based pasta sauce and cheese for dinner on the same day that total amount of chemical could tip them over the edge. HTH - I hope you find some answers and start getting some good results soon.