The adaptive nature of taste discrimination has been questioned on the basis that marked differences in taste thresholds for soluble sugars across mammals may not correspond to distinct dietary tendencies and further imply inaccurate prediction of the energetic value of food. Appropriate models of the evolution of taste, however, require not only consideration of adaptations to diet but also recognition of phylogenetic and allometric effects. Here, we analyse these factors in primates exhibiting various diets and covering a wide range of body weights. Taste thresholds for sucrose and fructose are negatively related to body weight overall but are commonly similar in closely related species irrespective of dietary specialisations. By contrast, major interspecific differences in the discrimination of quinine hydrochloride are observed in the absence of any allometric effect. We propose that this asymmetrical differentiation of sweet and bitter taste discrimination reflects divergent evolutionary trends for meeting energy requirements and for avoiding noxious substances.