The grey-haired, former paediatrician turned professor at Stanford University School of Medicine, now turned start-up founder, may be softly spoken but he doesn't mince his words.
A vegan, he's come to the World Economic Forum in Davos to evangelise about how ditching meat can save the planet.
At Davos, where helping the United Nations reach its goal of eradicating hunger by 2030 is one of its goals, he's got a receptive audience.