By chemicals, I am talking more flea powders, heartworm preventions, and other chemical I guess pesticides/poisons would be a better description. Food chemicals do not seem to affect him. He has not been tested, but my vet is monitoring him. She says that because his siezures have become so rare (maybe once every six months if even that often) to just keep an eye on him. She is the one that suggested that he may be hypoglycemic, though you are right, he is a bit on the large side for blood sugar issues.
Oddly enough, he did not start having them till he was almost two years old, right around the time he was microchipped...it has always made me wonder if his chip is somehow affecting him, but I have never heard of a microchip causing seizures. The fact that he didn't have his first one until such a late age also suggests that it is not hypoglycemia, but on the other hand, when he doesn't eat frequently he is more prone to seizures.
You dont know food chemicals dont affect him unless you have had him off all processed foods for a good period of time. You'd be amazed at how many dogs stop having seizures after things preservatives and dyes are out of their bodies.