You learn something new every day:) Apparently, gladiators ate a high-carb diet which was predominantly vegetarian and also consumed a sort of vitamin drink to assist with healing of injuries. This news made all the proponents of paleo and keto very nervous, while vegetarians and even militant vegans right away started claiming gladiators were part of the club (the 2nd link has a really cool video and great discussion in the comments section).
If you look at the original study called Stable Isotope and Trace Element Studies on Gladiators and Contemporary Romans from Ephesus (Turkey, 2nd and 3rd Ct. AD) - Implications for Differences in Diet (which by some reason I couldn't link to, so that you have to search for it on your own) right there on page 13 it says: In this study, the isotopic data suggest a mixed diet with a high share of vegetables.
I think it's quite obvious that they weren't really vegans or vegetarians in the modern sense of the word, and their eating patterns are actually quite typical for an average Roman, though they consumed more barley than wheat. Like it or not, meat was a luxury back then, but fish sauce, for instance was put on absolutely anything.
Mediterranean diet is more or less a continuation of the trend, and its Greek variety which encourages periodic fasting excluding all animal products except some seafood (the kind which doesn't bleed red like squid) is probably the closest to the ancient pattern.
Has anyone tried it? Feel free to share!