They studied a number of nations.

First one of course to mention is the US, the 7th day Adventists,
vegetarians live longer. Community I'm sure helps. Of course,
compared to Mormons, which also don't drink alcohol or smoke no such
differences were founds.

Other countries were not vegetarian. But their traditional means
yielded equal amounts of centenarians, male and female. The commonality
was they eat little meat, and a LOT of fresh vegetables and exercise daily.

It would appear that less meat is healthier, especially red meat, more
local produce, grow your own gardens if possible and exercise.

Not that modern society intoduces potato chips and junk food, the
benefits of modern civilization.