"The Game Changers" is billed as a documentary about meat, protein, and strength. Its mission is to show people that for many professional athletes, a vegan or vegetarian diet gives an edge over their competition.

And it can do the same for you in the gym, on the field, at work, and at home.

As the vegan strongman Patrik Baboumian says: "When people ask me, 'How can you get strong as an ox without eating meat?' my answer is, 'Have you ever seen an ox eating meat?' "

Researchers from the University of Sao Paulo in Brazil back up the documentary's claims. It turns out that it's the amount, not the source, of protein that matters when it comes to building lean muscle mass and strength.

Their research, published in the journal Sports Medicine, compared the effects of strength training on healthy men eating a vegan or an omnivorous diet. For 12 weeks, volunteers took in 1.6 grams of protein for every 2.2 pounds of their body weight every day, either from a mixed diet containing animal and plant protein plus a whey protein supplement or from a plants-only diet along with a soy-based protein supplement. Both groups increased lean muscle mass and strength equally.

The American College of Sports Medicine says that if you exercise regularly or are older, that's a good amount of protein to take in.

Vegans and vegetarians need to make sure they get enough protein daily from whole grains, tofu, and legumes, as well as a vegan or vegetarian protein supplement.