For the common plebs of Europe, and not connected and affluent people like DaVinci, how common was eating meat anyway? I was always under the impression that people were mostly 'vegetarians' by default due to the expense of meat, but ate it whenever they could save up for it
Follow up question, assuming that being a vegetarian in the 1500's was not unique to De Vinci; are there writings about animal welfare from this time or was it purely motivated by a desire to be healthy?
Isn't there some kind of grey area in Roman Catholicism where fish isn't considered "meat" in relation to Lent and fasting? Perhaps Da Vinci's vegetarianism would be the equivalent of a modern day pescatarian.
I'm not a historian and this is not an answer, but I would like to see a follow-up. I think OPs question is very good.
Eating nothing but vegetables might have marked you out as a Cathar which wouldn't have been very desirable as the Roman Catholic church had spent the last 2-300 years hunting them down and killing them^1. Carthars, according to one former adherent-turned-inquisitor, considered it to be a mortal sin to eat meat, eggs, and cheese, and in one court case in Toulouse, one claimant said that he ate meat, apparently to deflect suspicion away from him being a Cathar. While Catharism, and its spinoffs continued to percolate down the coffeepot of time, there was another strand of vegetarianism which went back a bit early to Pythagoras (and others), but had recently come into view with the Renaissance's penchant for translating things. Pythagoras had a thing for animal rights (as we might consider it today), and that idea also trickled down into Renaissance and Early Modern writers such as Erasmus, who had unflattering things to say about people who hunted animals, and More's Utopia (1516) had a section on the devastation that rearing cattle had on the land. Leonardo is part of this tradition (animals have feelings!) and his writings on this are fairly well known, if not completely verifiable.
However, placed against these examples (and some others), you have to place the vast amount of meat that was consumed by everybody, everywhere. Reading the accounts of what was eaten during feasts, and even if you take them with a pinch of salt, there was still a prodigious amount of food being consumed, most of it animal in origin (vegetables are suspicious but still consumed). This had consequences on the gut, and gout was a frequent visitor - Henry VIII probably suffered it among many others.
So as for being common, it wasn't - we can't really call it 'vegetarianism' because that doesn't really appear until the 18th century - but a few people lived austere, herb-oriented diets that we know of, but it's a question of whether they were vegetarians in the sense of 'meat is bad!' or whether it was 'meat makes me feel bad!' as a contemporary of Leonardo discovered when he began play with his diet after suffering intolerable indigestion. The latter is probably the more common perspective in general, but that is unlikely to extend much past the social classes who could afford to play around with their diet. The lower classes would have had much less choice in the matter.
Is it even true that he was?