A method of improving the immunity of a companion animal. The method can include administering to the companion animal a glucose anti-metabolite. The glucose anti-metabolite can be 2-deoxy-D-glucose; 5-thio-D-glucose; 3-O-methylglucose; 1,5-anhydro-D-glucitol; 2,5-anhydro-D-glucitol; 2,5-anhydro-D-mannitol; mannoheptulose; and mixtures and combinations thereof. The companion animal can be a dog or a cat. Improving the immunity can include altering the proliferative ability of T and B immune cells, and altering the relative distribution of immune cell phenotypes, for example.