Woody Harrelson became a vegan after realising he was lactose intolerant.
The clean-living eco-warrior is at the forefront of meat-free culture, but he admits it was a chat with a lady on a bus that prompted him to give up dairy.
The Messenger star tells Hustler magazine, "When I was 23, 24, I used to have a really bad runny nose, mucus, tons of acne, reddishness all over. A woman on a bus I took looked at me and said I was lactose intolerant.
"(She said), 'Stop dairy for three days, and all this is going to go away.' I stopped dairy, and sure enough it was gone three days later, never to return except when I get dairy accidentally."