The United States food system is highly centralized with only three of the fifty states producing more than 75 percent of U.S. fruits and vegetables. The high reliance on long-distance transportation and cold chains undermines the sustainability of the food system and adds to its vulnerability. This was most recently demonstrated during the COVID-19 pandemic which caused significant disruptions to food supply chains. A promising alternative is a more decentralized and localized food system which reduces the reliance on long-distance transportation and long supply chains. Since such a food system will likely consist of smaller producers, questions have been raised about its economic viability. This precipitated the idea of Food Hubs as market aggregators. The model was first introduced by the U.S. Department of Agriculture as a way to aggregate the agricultural product of small farms. It has since evolved to imply a more flexible food system that can complement various parts of the food supply chain. This study develops a framework to assess the social and environmental sustainability contributions of Food Hubs and especially of urban Food Hubs, since 80 percent of U.S. food consumers live in urban and metro areas. Using our framework, we conducted a content analysis of publicly available information for 50 Food Hubs in metropolitan areas across the United States. We find that Food Hubs contribute to environmental sustainability by reducing food transportation through sourcing from local farms. They also perform relatively well in contributing to lowering food waste and loss. Their contributions to improving water management and adopting more sustainable food production methods, however, appear to be less strong. Similarly, Food Hubs appear to enhance some of our selected aspects of social sustainability such as improving access to fresh and healthy food to local consumers, and organizations such as schools and hospitals. Only a few of the Food Hubs in our sample, however, address our other aspects of social sustainability such as improving food security. We conclude our study by offering an aggregate ranking of the sustainability contributions of our selected Food Hubs based on our assessment framework.