Most of the real issues has little to do with meat or no-meat and everything to do with what has been brain-washed into people as "healthy." The notion of breakfast being the most important meal of the day (nominally consisting of tons of grains and sugars with the grains turning into sugars as well) is completely wrong. It originated with an advertiser in the 1920's.
There's a lot more than this of course, but I had some serious gut issues and removing almost all grains and drastically lowering my sugar intact solved them. It's basically a war between the "good" gut bugs and the bad.