eliminating offending foods from the diet and giving the body rest time to cure the sensitivities is probably the best bet
wheat, gluten, dairy, corn, peanuts, tree nuts, vinegar, citric acid (industrially created with aspergillis niger -fruit citric acid is ok), sugar
these are very common triggers. if he eats any offending foods/chemicals at all, a reaction will likely happen and its very disheartening
trying out foods, rotatating, and eliminating is the best bet to figure out what personal intolerances are.
from there hopefully something like the makers diet will help..i am going to start it to see if it will help with my similar problems (candida, EBV mono, food sensitivities , IBS)