Romans in General were heavily into a wheat and grain diet. Hence the ‘bread and circuses’ bit. The legions had their own bakeries and they ground wheat, barley and other grains to produce the muesli sort of porridge eaten daily. There is an unconfirmed legend that pizza began from the legionaries during the Jewish War taking the shew bread the Jews baked and making it more palatable by baking it again with cheese and whatever vegetable toppings they could gather.
Nooooooooooooo...the "bread" in the "BREAD AND CIRCUSES" saying is about what was FREE/what the government gave out to the poor and lower classes.
Ancient Romans of higher classes ate meat...the flesh of fowls, fish, and animals; though not as much of the latter! I've seen ancient cookery recipes, from ancient Roman times and they ate things like dormice, various cuts of pork, and chicken, with unsparing amounts of ghastly garum, which is a stinking ( as it smelled to high heaven )fermented fish sauce, made from fish innards, heads, tails, and stuff like that.