Legume-derived foods have been shown to have comparatively low greenhouse gas (GHG) intensities whilst providing high amounts of nutrients. However, processing legumes into meat analogues can incur significant energy costs. Here, we undertake a comprehensive life cycle assessment of plant-based and (Brazilian and Irish) beef burger patties. Sixteen impact categories are supplemented with the carbon opportunity cost of land occupation, and benchmarked against nutrient density units (NDU) to provide holistic evidence on the potential contribution of plant-based patties to environmentally-sustainable nutritional density. Plant-based patties have a smaller environmental footprint across most categories, including a 77% smaller climate change burden, but incur 8% more energy use compared with Brazilian beef patties. Normalised scores (person equivalents) were significantly larger (p < 0.05) for the beef products across key categories including land use, acidification, and marine and terrestrial eutrophication. Sensitivity analyses indicated significant variance across impact categories if beef cattle are reared in South Africa, France or the United States, including a 16-fold difference in land occupation. Biophysical allocation of co-products reduced environmental burdens of beef burgers. However, owing to a 68% higher NDU per serving, reflecting higher fibre and essential fatty acid content, plant-based patties are associated with 81–87% less climate change and 92–95% less marine eutrophication per NDU compared with beef burger patties. Accounting for carbon opportunity cost of land further increased the climate change advantage of plant-based patties by 25–44%. A simple extrapolation indicates that switching from beef to vegetable patties in the UK could save between 9.5 and 11 million tonnes CO 2e annually, representing up to 2.4% of territorial GHG emissions.