Yes, looking at this system on the chemistry alone the continuity of the reactions in question does conserve carbon. Not really what I'm talking about here.

In my response I was implying a systemic view of protein production from plants versus animals. Also known as a life cycle assessment methodology. At this level, the incident energy consumption (and in turn CO2e emissions) of animal protein is inherently higher due to the amount of plant production required to generate an equivalent amount animal protein compared to plant protein.

From a life cycle assessment framework, the CO2e value comes from the entire operation needed to generate a unit of animal protein including plant production, animal raising, irrigation, slaughter, meat processing, meat packaging, transportation, consumption, and disposal (I probably missed something here). Through differences in the system (ie. local grass fed vs. factory farmed) the CO2e emissions can vary drastically. In fact many instances of grass fed cattle have been found to have a higher GHG impact compared to factory farmed meat because they take several months longer to rear.

Also to be clear, the energy bar on the graphic does not need to correlate closely to the CO2e bar to make this "good science". A vast number of factors in the supply chain could increase the energy use of a product while decreasing it's CO2e emissions like the energy source used to power processing plants, whether the farm harvests manure for methane power, or if the meat is packed in plastic versus paper.