There is really no evidence that a raw or vegan diet is any better than a omnivore diet that uses some discretion. My wife who actually has this thing called a degree in Nutritional Science agrees.
Meat (properly raised that is) is not bad, and for Christians, we are commanded to eat it. Peter was told by God to eat all forms of creatures and that God considered all creatures clean to eat. Paul told the Christians that when they are a guest at someone's house, they are to eat what is put before them. Meat or otherwise. The Bible says that Christians who don't eat meat are of weaker faith.
Veganism and raw diets can cause cause problems if you are not combining your foods correctly. I had a friend almost die during childbirth because her body was nutritionally unbalanced during labor. Even afterwards her health suffered until she started eating meat. She had been even craving meat, but did not eat it because her husband was a veg-head and she didn't want to upset him. Then she went on a long vacation without him, started eating meat, and felt 100% better.
Why do vegan and raw diets seem to work? Its VERY SIMPLE, it forces the practitioner to PAY ATTENTION TO WHAT THEY ARE EATING. No junk food. No processed food. No fast food. Etc. If an omnivore does the same thing, they will have similar beneficial results.