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

Despite the clear effect of food resources on wildlife disease dynamics, few studies have investigated how shifts in diet, specifically macronutrient content, shape vertebrate host responses to infection. While each individual macronutrient plays a vital role in physiological processes necessary for pathogen defense, it is often difficult to disentangle the role of an individual macronutrient on disease pathology. We explored the effects of dietary macronutrient composition on disease pathology and feeding behavior of canaries ( Serinus canaria domestica) infected with Mycoplasma gallisepticum (MG). First, we provided canaries with isocaloric diets comprised of identical ingredients that varied in macronutrient content (high-protein or high-lipid) then MG- or sham-inoculated birds. We then offered both diets to canaries before and after MG- and 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 to 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 host tolerance and pathology and thus affect host-pathogen transmission dynamics.