I have found foods to be very important with regards to temperment. If I get lax at all with my DD's diets, I either get bloody curtling screaming for 6-8 hours a day, or violent diarrhoea. Its painful for everyone. Certain things set either child off. If DD2 gets too many salicalytes in her diet she gets horrible diarrhoea, this is in avocados, bananas and tomatoes... so not even "bad" foods. For DD1 its most additives and chemicals that she reacts to behaviourally. BUT I found that even freshly squeezed apple juice sets her off. Any form of apple juice has serious behavioural side effects. She could drink a whole litre of limonaide and be fine... but give her 1/2 cup of apple juice and she is a mess.

Have a look into elimination diets or google Sue Dengate or Fail safe diets. Its all about behaviour & diets.