The present invention relates to methods of determining the levels of endogenous margaric acid before and after a meal in a companion animal, wherein the meal is a pet foodstuff having a particular protein to fat ratio, which is useful in increasing the endogenous levels of margaric acid post-prandially and having the beneficial effects as described herein. The pet foodstuff comprises a ratio of protein to fat of 1 :0.27 to 1 :0.63 on a gram:gram as fed or dry matter basis. The invention also relates to methods of determining levels of lipid metabolites, such as palmitic acid, diacylglycerol (DAG), triacylglycerols (TAGs) and ceramides before and after a meal in a companion animal, wherein the meal is a pet foodstuff having a particular protein to fat ratio, which is useful in controlling,, regulating and stabilizing lipid metabolites post-prandially to prevent and/or reduce lipotoxicity in the companion animal.
