The article says the higher levels of strontium in their bones is from vegetables, but this source[1] says it's from consuming a tonic of plant ashes after their fights. They're trying to then correlate this to vegetarianism, but it's unrelated: they were artificially increasing their strontium-calcium ratio.

It's pretty well documented that bread and porridge were the staple foods of the Roman world[2]. You could mix anything into your porridge, from vegetables and dried fruits to expensive things like olive oil, meat and fish. Garum, a fish-based condiment, was put on everything.

Their higher carb intake is probably not because they were avoiding meat or protein, but because they just needed more calories, and carbs like grains and beans are a cheap plentiful source of them. There were many different kinds of gladiator from all walks of life, so it's insane to think at least some didn't eat meat. In fact, in the bone studies quoted, at least 2 of the 22 gladiators analyzed showed elevated consumption of meat.

If you're a slave gladiator and your owner is a cheap bastard, then your dinner (like the rest of the poor people of Rome) will be mostly carbs. But if you're a well-off gladiator, you probably ate meat when you felt like it.

[1] https://www.sciencedaily.com/releases/2014/10/141020090006.h... [2] https://en.wikipedia.org/wiki/Ancient_Roman_cuisine