Ranking of different foods/commodities by #environmental footprints changes based on production differences, but also based on the assumptions of the modeler(s) and the functional unit (denominator of the footprint). Here's global livestock with crude protein as the denominator 
Here's a UK specific example using nutrient density as the functional unit where beef has a lower carbon footprint than chicken.
Here's a ranking using essential amino acids as the functional unit that shows beef with less land use than peas.
Here's a ranking that shows processed vegetables having a higher GHG footprint than meat products, and sugary sweets have the lowest footprints.
Life cycle assessments that generate footprints are great tools, but comparing products assumes common modeling methodologies, true fungibility/nutritional substitution across foods, and typically ignores any indirect effects of major changes or potential unintended consequences.
Brushing over these limitations and uncertainties is bad IMO & the impact categories we examine with LCA are currently limited. Critical components to a sustainable food system, like soil, ecosystem services, livelihoods, & affordability don't usually make the cut
