Coral reef fisheries are a vital source of nutrients for thousands of nutritionally vulnerable coastal communities around the world. Here, we evaluated the potential effects of expanding sustainable-use marine protected areas (MPAs) to improve the nutrition of coastal communities. Using information from underwater visual surveys from 2,518 sites located in 53 countries, we developed a Bayesian hierarchical model to estimate the average effect of existing sustainable-use MPAs reef fish biomass and explored how that may alter fish catch, and the nutrients supplied to local communities. We then estimated the potential nutritional benefits of expanding sustainable-use MPAs to all non-MPA coral reefs globally. We found that existing sustainable use MPAs have on average 15% more biomass than open access reefs. Translating this into catch, we estimated that expanding sustainable-use MPAs could increase catch potential by 0-20%, which could prevent 0.53-1.95 million cases of inadequate micronutrient intake globally, a fraction of the people who would continue to be sustained by this foundation of coastal food systems. Our study estimates the potential nutritional benefits of expanding sustainable-use MPAs and pinpoints locations with the greatest potential to reduce inadequate micronutrient intake levels, critical knowledge given the strong international movement to cover 30% of our oceans with MPAs by 2030.