I definitely try to keep some protein in our 4 year old. She has much bigger mood swings if she is just eating carbs. Cheese, yogurt, nut butters, milk, nuts, sandwich meat, boiled eggs are all good easy proteins that work well for her. My 4 year old is very dramatic and emotional (chock full of OEs), so I feel your pain! The food thing does help a bit though!
We also encourage "using your words" and speaking without whining. I won't talk to her or help her until she can pull herself together enough to talk at least somewhat rationally. Sometimes that involves just saying "Come see me when you're ready to talk" and walking away.
Oh I don't know if the tantrums or whining is worse
I'm going to make sure that he's getting a lot of protein as well.
I'm so glad that I found this board. When I mentioned a change of diet to my friends for his problems they looked at me like I was crazy!