I was just reading this article by David Katz, M.D. in HuffPo:
So while this starts out with some reservations about what can be scientifically proven about diets, and Katz is not a vegan himself, he comes around and supports veganism (or at least mostly plant-based diets) because of ethics and environmental reasons.
I think when most vegans say that the vegan diet is the best for human health, it's meant as a statement of belief, not a statement of scientifically established fact. That belief might of course be based on supporting scientific evidence, but not definite proof.
More: Zeal, Veal and Veganism | David Katz, M.D. (20. July 2015)When my vegan friends and colleagues say that a vegan diet is categorically the best for human health, it is an excess of zeal. We simply do not have evidence to substantiate the claim. I know; I've looked- hard.
If you are inclined to doubt my assertion, just consider what such evidence would look like. [...] I think what we really mean is: leads, on average, to the most years in life, and the most life in years over an entire lifetime. The "best health" is enjoyed by people who live long, and prosper from their enduring vitality.
Given that, the trial to show that any given diet is truly "the best" has not been done, and is unlikely ever to be done.
So while this starts out with some reservations about what can be scientifically proven about diets, and Katz is not a vegan himself, he comes around and supports veganism (or at least mostly plant-based diets) because of ethics and environmental reasons.
I think when most vegans say that the vegan diet is the best for human health, it's meant as a statement of belief, not a statement of scientifically established fact. That belief might of course be based on supporting scientific evidence, but not definite proof.