A growing and ageing population increasingly adds pressures on the world's resources to provide healthy, diverse and sustainable foods, of which proteins are an essential component. Increased demand for animal-based proteins has a negative impact on the environment and climate change, and the development of plant-based protein production as well as alternative sources for direct human consumption could represent suitable sustainable alternatives. The NSLive 2020 conference, ‘Proteins: sources, benefits and global challenges’, included presentations related to the physiological determinants for protein requirements, considering varying needs across the lifespan as well as sustainable development for protein production. Papers presented in this issue provide insights on the latest methodological developments to assess protein metabolism, as well as on various issues related to protein nutrition, such as vegan and vegetarian diets in children, metabolic health, sustainable protein production and healthy ageing. Adequate protein intake is essential for optimal development and healthy ageing, but current recommendations for protein and amino acid intakes may need revising to optimise physiological requirements, particularly for elderly people. Greater political will, with integrated involvement of wider stakeholders and industries, is essential to address sustainable protein production while ensuring food security.