The consumption of meat and dairy products raise enormous environmental concerns. Circa 80% of global greenhouse gas emissions (GHG) from the livestock industry originate from beef, milk and pork production. Changing the production and consumption of meat and dairy products is considered to offer an important contribution to achieving the Paris Agreement climate targets (UNFCCC, 2015), and could reduce the import of soybean meal to Europe from countries where it is linked with deforestation. However, individual diet substitutions may have indirect and unintended environmental consequences across interlinked livestock systems – hence a wider assessment of impacts of consumption changes is required using consequential life cycle assessment (LCA). In this study, we investigated the environmental consequences of two independent yet interconnected diet choices in a German context: (i) replacing dairy milk with soy milk, and; (ii) replacing beef meatballs with pea protein balls. We related commodity demand to detailed agricultural rotations and land use changes via farm scale economic modelling coupled with consequential LCA. The substitution of beef meatballs with pea-derived protein balls can result in GHG savings of 2.4 kg CO2e per 100 g serving, and up to 7.3 kg CO2e per 100 g serving if spared land is afforested. Environmental problems related to nutrient leakage such as acidification and eutrophication are also mitigated. Meanwhile, unless accompanied by dramatic reductions in beef consumption, the substitution of cow milk with soy-based milk does not lead to significant GHG mitigation owing to the displacement of dairy-beef production to less efficient suckler-beef systems. Nonetheless, land sparing by cow milk substitution could support overall GHG mitigation if combined with afforestation. This study confirms that legumes can play an important role in diet transitions towards climate neutrality, especially via substitution of meat (as opposed to dairy) products.