SiameseFighter is right, very meaty foods can cause bloat in Mbuna. I should have been more specific as some fish from Malawi can handle meaty foods. Here's a quote from an article on Cichlid-forum.com explaining more.
"Mbuna are exclusively Herbivores (with the exception of Labidochromis). They spend all day picking and scraping at the thick mat of algae that covers the rocky shoreline of Lake Malawi. This algae is their primary staple, which is supplemented with the insects and crustaceans that live in the algae. While Mbuna, officially, are vegetarians, they will eat almost anything that can fit in their mouths. Careful attention to their diet is required if you want to keep these fish healthy.
The digestional tracts of Mbuna are made for vegetable matter. They have long intestines designed to extract the proteins and carbohydrates from the hard-to-digest algae. Cows and other ungulates use several stomachs to digest grass. Mbuna, on the other hand, do it with only one stomach and a very long intestine. If you feed them too much animal protein (e.g., worms, shrimp, feeder fish), it will only be a matter of time before they develop an intestinal blockage, swell up, and die from the infamous Malawi Bloat."