Unique nutrient requirements of cats appear to bediet–induced evolutionary adaptations

Cats have requirements for essential dietary nutrients additional to those needed by other animals. The object of this review is to relate the idiosyncratic nutritional requirements of cats to activities of enzymes involved in the pathways of these nutrients. The high protein requirement of cats follows from the lack of regulation of the aminotransferases of dispensable nitrogen metabolism and urea cycle enzymes. The dietary requirements for the amino acids taurine and arginine are consequences of low activities of two enzymes in the synthetic pathways of these two nutrients that have a negative multiplicative effect on the rate of synthesis. Cats have obligatory dietary requirements for vitamin D and niacin due to high activities of enzymes that catabolize the immediate precursors of these vitamins to other compounds. The requirement for preformed vitamin A appears to be the result of deletion of enzymes required for cleavage and oxidation of carotenoids. While the requirement for the long chain n–3 polyunsaturated fatty acids has not been defined, low activities of desaturase enzymes indicate that cats may have a greater dietary need for these nutrients than other animals to maintain normal plasma concentrations. The present day nutrient requirements of domestic cats support the thesis that their idiosyncratic requirements arose from evolutionary pressures from a rigorous diet of animal tissue. These changes favoured energy conservation by deletion of redundant enzymes and modification of enzyme activities to result in metabolites more suited to the cat’s metabolism. However, our retrospective viewpoint allows only recognition of association rather than cause and effect.