Just wondering what a good high fiber diet would be with protein and stuff so that it’s natural food and healthy.

i want to get a 6 pack and i was wondering if a high fiber diet help burn belly fat and eat protein for one meal every day

i run 2-3 niles every day
i don’t eat fast food and fried food

so this is what im planning to do:
breakfast- 2 bowls of cereal
lunch- protein food(chicken, lamb, etc) with rice
dinner- oatmeal

Experimentation with a high fiber/whole grain diet for 8 months made me surprisingly extremely, severely ill. I was completely cured as soon as I resumed my original diet. All I can find is data praising high fiber diets. Is there any information that suggests that these diets can be harmful?
Has this happened to anyone else?