As a lifelong vegetarian - who is NOT an extreme athlete, just an average executive assistant in the corporate world - I consider good diet as the primary contributor to my good health into my late 60s. But I had never heard the kind of shocking evidence from the experience of athletes who (like me) have been culturally persuaded all our lives that humans must eat animal protein to be healthy and who found out otherwise by eating the plant-based diet and measuring results.
That being said, I do not find these testimonies in support of a plant-based diet surprising at all. I have observed my own evidence personally. I come from a large family (similar genetic makeup) who all eat the usual American diet which emphasizes animal protein as a necessity, and I feel and look younger than all of my siblings who are younger than me. Diabetes runs in my family, my sisters have to address it medically, but I've never been diagnosed with it. My blood pressure and cholesterol have always been low and well below the desired targets.
I have a 12-year old nephew who has embraced a plant-based diet based on his concern as one of the youngest generation to live on this planet, for its well-being. This documentary also briefly covers the compelling arguments for reducing the production of animal protein for the sake of the longevity of the planet.
So it's kinda all there -- from an unusual perspective: Those who were reluctant to consider a plant-based diet to begin with.