That's right: most ancient gladiators were vegetarians, but not necessarily for reasons you might think.

The gladiators of the ancient world were fearsome warriors who often had no choice but to fight or die. Many aspects of their lives were optimized to tailor them to the blood sport.
When you think of a gladiator's diet, it's easy to envisage a mighty warrior messily devouring a juicy steak. The truth, it seems, is that many gladiators were actually vegetarians, eating a diet consisting of health foods such as beans, grains, oatmeal, and dried fruit.
These were often washed down with a drink that consisted of vinegar and plant ash, used like a modern-day sports drink to fortify the body after physical exertion and promote bone health.
Researchers believe that despite their meat-free diet, gladiators were well-built, muscular people who were larger than modern-day athletes, giving them extra protection from the blows.
German researchers confirmed the theories about the Roman gladiator diet after they tested corpses in a Roman cemetery from the 2nd century.