Any suggestions for dealing with elderly that act like children when it comes to food; and yes I know he has dementia.

My father-in-law is 82 years old, and is on a lactose, low salt, low fat diet. This makes it hard to find things he can eat for breakfast. His norm is 1 egg, 2 turkey sausage links, and either fruit, 1/2 English muffin w/ 1 tsp. Peanut Butter, or 1 waffle. Now if I come in with it, it's suddenly 'I will throw it up" if he does not like it. You ask what what he wants, it's whatever. I am going to pull my hair out of my head. Now, since he came from respite care last week, all he does is sleep. His hours are so messed up. He has to eat because of meds that need to be taken w/ food. If I give him a cereal bar... (which just like a cookie), that's all he wants for the next week. He has a weight problem,too.