Animal models using rabbits were developed to accumulate a variable body fat mass (FM) in two groups of animals while the fat-free mass (FFM), eg, total body protein, was maintained essentially similar between the groups. Thiobarbituric acid-reactive substances (TBARS) were measured as an index of lipid peroxidation and were found to be higher in the whole-body tissues of animals with a higher FM. Bacterial toxin (lipopolysaccharide [LPS]) also induced higher lipid peroxidation in animals with a higher FM, with a concomitant incidence of bloody mucous diarrhea. To our knowledge, this is the first evidence to show the effect of body FM to aggravate toxin-induced infections leading to diarrhea. The overall results suggest further investigations to explore the possible role of body fat in infectious diseases in humans.