The purpose of this study was to investigate patterns of dietary generalism in a large widely distributed mammalian omnivore, through the lens of macronutritional niche theory. To that end, we selected the brown bear (Ursus arctos) as an exemplar model species. The brown bear has an ecologically and geographically wide (i.e., circumpolar) distribution (Pasitschniak‐Arts, 1993). Across its range, the brown bear has a polyphagous diet consisting of a wide range of foods that vary in physical, ecological, and nutritional properties, depending upon both seasonal and local availability (Bojarska & Selva, 2012; Coogan, Raubenheimer, Stenhouse, & Nielsen, 2014). As apex predators, brown bears consume a range of animal prey, such as small and large mammals, insects, fish, and birds (e.g., Ciucci, Tosoni, Di Domenico, Quattrociocchi, & Boitani, 2014; Rigg & Gorman, 2005). Brown bears also consume a variety of graminoids and forbs, consume both soft mast (i.e., fruit) and hard mast (i.e., nuts), and possess the ability to dig for and consume belowground vegetation (e.g., roots and corms, Hamer & Herrero, 1987). Brown bears are also known to obtain a variety of both plant‐ and animal‐based foods from anthropogenic sources, including grain, livestock, and human food waste (Gunther et al., 2004; Murray, Fassina, Hopkins, Whittington, & St Clair, 2017). In the context of the multidimensional nutritional niche, the brown bear can thus be characterized as a generalist in both food exploitation (level 1 above) and food composition (level 2 above).