Please do not use Dean Ornish as a reference. An ethical vegetarian, he has a history of cherry-picking research to support that as the only healthy option. Evolutionary, cultural and epidemiological research are secondary to that goal.
He first defended very low fat diets to demonize carnivory. His original diet included fast-digesting carbohydrates like bread and rice. Those have been shown to cause insulin resistance and obesity when not buffered by fat, fiber or calorie restriction. He only reduced those after DASH demonstrated the issue.
When research showed both that some fats were essential and that calorie restriction, not macronutrient ratio explained his diet's limited benefits, he migrated to a low fat vegetarian diet. He has not adopted a medium fat diet in spite of its superiority within the DASH diet envelope.
Finding that subjects did not honor his diet long-term without regimentation, he provided meditation, stress-reduction and counseling for the vegetarian arm of a comparison with an ad-libitem conventional diet but he titled the study as recommending his diet in isolation.
Sadly, this kind of ideological bias is rife in Huffington Post.