That's interesting! Dean Ornish does say that no nutrition, lifestyle, or conventional medicine treatment program, is effective for everyone. I myself tried all sorts of diets, except full carnivore - was too scared to try that one! But I've tried keto, paleo, and so on, mainly cos I have an autoimmune disease. Many diets helped me but only temporarily. I actually didn't want to try vegan, for whatever reason, but finally I did, and near-vegan is the diet I've had the longest success with. The current science definitely favors plant-based, but there's so much we don't know yet. There's thousands of studies about plant-based on pubmed, barely 200 on paleo, and I can't find any on carnivore that isn't about mammals other than humans! Definitely under-researched. Who knows how many decades, or more, it will be before we fully figure these things out.

But there's another serious problem with carnivore, and that's sustainability: we can't feed 8 billion humans on a regular omnivore diet, much less one that's only meat! Individuals in rich countries can do it for now, but long term it's impossible, unless technology somehow solves the problem, as it often does (lab-grown meat, say).