Schwarzenegger, who has encouraged his followers to cut down on meat in the past, said: "I ate a lot of meat - I ate my 10, 15 eggs a day. I had my 250 grams of protein in a day because I weighed 250 pounds.
"As I got older and I started reading up on it, I recognized the fact that you really don't have to get your protein from meat - or from animals. So we started going more in a direction of a vegetarian kind of diet.
"Now we're doing it the right way, with spices, and all of a sudden I love it much more than the meat."
The star also said ditching meat resulted in his cholesterol dropping to around 109 - the lowest it had ever been in his 'entire life', but didn't clarify whether he is now vegan or still vegetarian.
Schwarzenegger shared a trailer of The Game Changers on his Instagram earlier this year, saying the documentary 'terminates outdated myths about protein, strength, and performance'.
"I ate a lot of meat. They show these commercials - 'steak, that's what a man eats' - selling the idea that a real man eats meat," Schwarzenegger commented.
"But you've got to understand - that's marketing. That's not based on reality"
The Game Changers, directed by Oscar-winner Louie Psihoyos and executive produced by Oscar-winner James Cameron, 'documents the explosive rise of plant-based eating in professional sports, mixing real-time, groundbreaking science with cinematic stories of struggle and triumph'.
"The film features some of the strongest, fastest and toughest athletes on the planet - and it's backed by them too - with additional EPs including Formula One champion Lewis Hamilton, top-ranked tennis player Novak Djokovic, and nine-time NBA All-Star Chris Paul," says the film's description.
Game Changers will be available in theatres across the world from September 16.
You can buy tickets here