SummaryThere is a growing interest in vegetable‐based sources of proteins. Despite its high nutrient content, lupine has been rarely exploited as a protein source due to the presence of high levels of non‐nutritive compounds such as alkaloids, which impart a bitter taste. Here, we evaluated the effect of debittering and solid‐state fermentation on the nutritional contents of three lupine varieties (Lupinus mutabilis Sweet). These processes induced significant changes (P < 0.05) in the nutritional composition of the three lupine varieties (INIAP‐450, INIAP‐451 and Criollo) and increased the protein levels to 644.55 g kg−1 (Criollo variety) and the levels of several constituent amino acids such as valine (54.62 g kg−1), methionine (42.47 g kg−1), isoleucine (59.27 g kg−1) and leucine (76.32 g kg−1). The ether extract of INIAP‐450 showed increased levels (up to 244.03 g kg−1); especially, monounsaturated fatty acids (559.78 g kg−1) and polyunsaturated fatty acids (293.17 g kg−1) were observed. The omega‐6/omega‐3 ratio in the debittered grain oil reached the minimum requirement established for good‐quality oils (5/1). However, the levels of other components decreased, showing levels up to 13.04 g kg−1 (total starch) in the Criollo variety, 22.62 g kg−1 (resistant starch) in INIAP‐450, 6.53 g kg−1 (potassium) in INIAP‐451, 46 g kg−1 (iron) in INIAP‐451 and 29.75 g kg−1 (zinc) in INIAP‐450.