There is a need to find sustainable alternative protein sources in order to meet the increasing protein demand of the growing population. Legumes such as faba beans are underutilized protein rich sources and can be valorized as hybrid protein ingredient through dry fractionation technologies. Also, cereal side streams can be interesting sources towards multifunctional protein ingredients. The aim of this study was to assess the environmental impacts of the production of oat protein concentrate (OPC) and faba bean protein concentrate (FBC) using life cycle assessment (LCA) methodology and to compare the impact per kg protein to other relevant proteins. The OPC is obtained as a side stream of the beta glucan extraction process, which also produces valuable oat oil, while FBC is the only main product obtained from dehulled faba beans. Average European oat cultivation and faba bean cultivation with low and high yield were modelled. Data for protein concentrates production was from real factories who have suitable facilities, but are not currently producing concentrates commercially. The major hotspot in the carbon footprint of oat protein concentrate comes from energy consumption in processing. For faba bean protein concentrate, energy consumption in processing is lower and cultivation of faba bean is the main hotspot. The carbon footprint of oat protein concentrate is more than 50 percent lower, compared to dairy proteins per kg protein, while the carbon footprint of faba bean concentrate protein is 80–90 percent lower. Compared to legume protein sources, OPC has four times higher impacts. This is mainly due to the lower amount of processing steps needed to reach high protein content concentrates from faba beans resulting mainly from relatively lower level of lipids, which enables more energy-efficient dry separation, and high initial protein content of legumes compared to cereals. Moreover, legume cultivation requires very little nitrogen fertilizers due to symbiotic N2 fixation. This study shows that OPC and FBC have lower carbon footprints than animal protein sources. However, it should be remembered, that the environmental impacts of OPC are very sensitive to the allocation method and allocation basis. In this study economic allocation was used and prices of the different products (OPC, oat oil and beta glucan) play a key role in defining the climate impacts of OPC.