The protein shift, or transition, entails a reduction in the production and consumption of animal-source foods, and an increase in plant-based foods and alternative proteins, at a global level. The shift is primarily motivated by the need to minimise the impact of the food system on social-ecological systems. We argue that rather than focusing singularly on transitioning a ‘protein gap’ in diets, redressing the ‘justice gap’ is a prerequisite for transformative change in food systems. In this context the justice gap is understood as the gap delineating those who have access to just food systems and those who do not. To substantiate our argument a justice lens is used to analyse the political–economic dimensions of such a transformation and to propose that the future of protein must engage with three core elements to be transformative—disruption, innovation and redistribution. Disruption entails challenging both the food trends that encourage the ‘meatification’ of diets, and the influence of ‘Big Meat’ in perpetuating these trends. Innovation emphasises that true novelty is found by designing justice into practices and processes, rather than by firing alternative protein silver bullets within existing food system paradigms. Redistribution stresses that food system redesign is predicated upon establishing fair shares for remaining protein budgets, using approaches anchored in contextual specificity and positionality. Through the application of a justice framework, we expose existing food system injustices related to production and consumption of protein, invite discussion on how such injustices can be addressed and reflect on implications for food system transformations. By reshaping the crux of the protein debate around the more salient concern of the justice gap, food system transformation can take shape.