It is pretty hard to be a vegetarian in the US and eat low carbon food. If you grow it yourself or only buy from tiny farms maybe. AG in the US is petroleum based top to bottom.
Since all inputs to animals are coming from fertilizer-based crops, by definition meat is an order of magnitude more carbon intensive than simply eating plants.
Unless you assert that most animal feed is significantly less carbon intense than plants grown for human consumption, this holds. While grazing animals do exist, the vast majority of animal feed is farmed.
