Dietary changes can affect both human health and the environment. Reducing meat consumption, especially ruminant meat, has been proven to significantly reduce greenhouse gas (GHG) emissions, reduce agricultural land use, and improve human health. Whereas the shift to a plant-based diet from meat is by far the most commonly investigated dietary change pattern, nutrient-rich forage fish with a low carbon footprint is receiving increasing interest from a global food system perspective. In this study, we attempted to fill the current research gap to better understand the environmental and nutritional impacts of forage fish as a substitute for ruminant meat by 2050. We developed environmental- and nutrient-based consumption scenarios for meat substitution. Global ruminant meat demand and potential forage fish supply were projected using a global economic model and catches over the last few decades. We found that the potential forage fish supply could replace 10 % of global ruminant meat consumption, resulting in global ruminant-related reductions in total GHG emissions and land use by up to 15 % and 10 %, respectively, by 2050. Such a dietary change could also increase the intake of essential nutrients, such as omega-3 fatty acids (DHA and EPA), vitamin B12, and calcium, especially in deficient regions. Our analyses highlight the potential of forage fish as part of a portfolio of sustainable dietary solutions, while effective fisheries management and sociocultural acceptance of forage fish consumption are necessary to realize the potential of forage fish.