Within the dietary repertoire of any animal species, some resources are crucially important for species fitness, influencing the socio-ecology, geographic range and population density. Namely, preferred and fallback resources are hypothesized to exert evolutionary and ecological pressures in a way that other resources do not. Fallback foods are those whose consumption increases significantly inversely to the availability of preferred food. They are typically available over extended periods of time and have low nutritional value. In contrast, a preferred food is a seasonal resource of high quality and consumed disproportionately when available (significant positive relationship). From a three-year study identifying and quantifying fruit remains in western lowland gorilla faeces and monitoring fruiting phenology of adult trees in a site in southeast Cameroon, we operationally define preferred and fallback fruit species. We further distinguish ‘staple’ and ‘filler’ fallback fruits, where the former can seasonally represent the sole fruit supply, but the latter never does. Among 24 important fruit species, four fulfil the characteristics of fallback food, three as filler and one as staple (Uapaca spp.), and four others as preferred food. As Uapaca trees are characteristic of secondary growth forests, like the other well-known fallback food taxon, terrestrial herbaceous vegetation, the role of past disturbances on present day habitat suitability is discussed.