The present invention relates to a method and nutritional supplement which stimulates appetite and slows metabolism of a mammal, thereby enhancing weight gain for the mammal. The method of enhancing weight gain of the mammal comprises administering to the mammal an effective amount of at least two types of alkamide or isobutylamide compound extracted from Echinacea species along with an antioxidant and optionally minerals. The nutritional supplement of the present invention comprises an antioxidant and at least two types of alkamide or isobutylamide compounds derived from Echinacea species. Minerals such as zinc and magnesium can also be added to the nutritional supplement to provide even better effect.