Individual macronutrients in the diet contribute to immune processes and the immune system’s ability to efficiently clear an infection. Some studies have shown that infected animals will consume protein to enhance survival, while other studies have shown that lipids can reduce inflammation and increase antibody production. By altering the ratios of specific macronutrients, the interplay and individual impact they have on immune responses can be better understood. Using an avian host-pathogen system and isocaloric diets, I explored the effects of dietary macronutrient composition, specifically lipid and protein content, on disease pathology and behavior of canaries (Serinus canaria) infected with Mycoplasma gallisepticum (MG). Female canaries provided a protein-rich diet, whether infected or not, consumed more calories per week than female canaries on a lipid-rich diet. Also, all birds that were infected exhibited illness-induced anorexia in the first week post infection. Infected birds also experienced a significant decline in fat scores and body mass post infection. Diet did affect disease pathology; infected birds on the lipid diet experienced clinical signs of infection (swollen eye conjunctiva) longer than birds on the protein diet, as measured by eye score. Despite these differences in eye score over time, post-infection levels of MG specific antibodies were not significantly different between infected birds fed the different diets. These data indicate that diet macronutrients could play an important role in individual variation in disease severity among hosts infected with a pathogen. These data suggest that host diet could affect pathogen growth and reproduction, and thus, disease transmission. Future plans include estimating pathogen load in birds used in this study.