A high-lipid diet leads to greater pathology and lower tolerance during infection.

Altered food landscapes contribute importantly to wildlife disease dynamics and may play a critical role in host heterogeneity in disease outcomes through changes in host diet composition. We explored the effects of dietary macronutrient composition on disease pathology and feeding behavior of canaries (Serinus canaria domestica) infected with Mycoplasma gallisepticum (MG). In the first experiment, we provided canaries with isocaloric diets composed of identical ingredients that varied in macronutrient content (high protein or high lipid) then MG- or sham-inoculated birds. In the second experiment, we offered both diets to canaries before and after MG or sham inoculation. In experiment one, high-protein diet birds consumed more food than high-lipid diet birds and experienced a more pronounced decrease in food intake after infection. High-protein diet birds were more tolerant to MG infection, exhibiting reduced pathology when compared with high-lipid diet birds, despite the two treatments having similar levels of MG-specific antibodies and MG loads. When birds had access to both diets, they consumed more of the high-protein diet and experienced pathology for less time than lipid- or protein-restricted birds. These results highlight that macronutrient makeup of the diet can shape vertebrate host tolerance and pathology, which has direct implications for host-pathogen transmission dynamics.