There is Dotsie Bausch, a seven-time U.S. national cycling champion who, at 39, was the oldest cyclist to ever qualify for the Olympics, not to mention return home with a silver medal. There is Patrik Baboumian, the former Germany’s Strongest Man who holds multiple world records, including lifting a staggering 1,213 pounds over his head. There is one of the greatest ultramarathoners of all time, Scott Jurek, who ran the Appalachian trail in 46 days, eight hours, and seven minutes—three hours faster than anyone else at the time, and months shorter than the average hiker. There are Roman gladiators, gorillas, and Arnold Schwarzenegger, all of whom have two things in common: superpower strength, and a plant-based diet.

“When I first saw the study that indicated Roman gladiators were eating almost exclusively plants, I thought it had to be bs,” says James Wilks, a special forces trainer, winner of The Ultimate Fighter, and the star of The Game Changers, a new documentary set out to debunk the myth that meat is necessary for protein, strength, and good health through an exhaustive—and persuasive—lineup of tests and interviews with pro athletes, soldiers, and scientists. “After thousands of hours of research, [I realized that] everything I thought about nutrition—eating meat and eggs and milk for your bones—was totally untrue . . . I was shocked.”

What was once a passion project for Wilks, a way to recover as quickly as possible after an injury took him out of the ring and onto the couch, with plenty of time to poke around the Internet, swiftly became a personal mission. About midway through his research, his father, a healthy, active meat eater, had a heart attack and required emergency surgery that left him with two stents and few options. Wilks’s shock quickly morphed into anger, directed towards a meat industry that, he says, has been profiting off the foods that may increase risk for preventable diseases such as heart disease, cancer, and diabetes.

And so, Wilks called in the big guns. “I liken it to a MMA [mixed martial arts] fight, with three rounds,“ he says of the six-year filmmaking process, which started with a Craigslist-bought handheld camera and eventually led him to an award-winning documentary team that includes director Louie Psihoyos (The Cove), executive producer James Cameron, and writers and editors that are responsible for the likes of An Inconvenient Truth, Chasing Ice, and the non-commercial, fact-based website NutritionFacts.org. The result is a groundbreaking picture, which premiered at the Sundance Film Festival, that follows top athletes and regular people alike across four continents for the pursuit of truth in the name of protein. Here, the five most fascinating facts surrounding a plant-based diet.