This is not new. It's been around for a long time. Sylvester Graham, the guy what invented Graham crackers and Graham flour (and who had some really odd ideas about sex), was a whole grain and veggie kind of guy. So was Harvey Kellogg, an apostle of healthy eating (with equally odd ideas about sex and, of course, bowel movements), whose brother founded the Kellogg cereal empire. Bread has been called the Staff of Life since ancient times.
All this comes from those who look at the Neolithic Revolution in agriculture and see the human organism as fundamentally designed to run on plant matter. Health and religion both look to those days. Ah, but later anthropologists looked at our evolutionary history and said, "what about before the domestication of crops? what did we eat then?" And the answer is, Meat.
Anthropologists point out that the driving force in human evolution, dietarily speaking, was meat -- and the FAT that comes with it. Back in the days when our ancestors were scavenging carrion, fat was scarce, and so we came to greatly desire it. This is why "fat makes food taste better," to quote Julia Child. And from our increasing skill at hunting came a diet richer in protein and fat, which led to bigger brains and the development of modern Homo sapiens.
The biblical story of Cain and Abel -- in addition to whatever else it is fraught with -- is a story of two different lifestyles. There is Abel, the pastoralist, and Cain, the farmer. The Old Testament was written by pastoralists, and their opinion of Cain is well known. If the farmers had written Genesis, Cain might have gotten better press.
But let's get real. The best diet is to eat less and exercise more. In the end, unless you have a specific condition that shapes your body's needs, it doesn't matter if you're a vegetarian or a carnivore.