Food supplement for increasing lean mass and strength

Food supplement compositions and their methods of use in increasing lean mass and/or muscle size and/or strength in individuals, particularly, athletes is described. The food supplements described comprise a substance which increases nitric oxide production in the body, and, a source of amino acids. Other food supplements described comprise a substance which can enhance and/or mimic insulin activity, and a source of amino acids. The food supplement compositions described are suitable for supplementing the diet of an athlete and particularly for enhancing an athlete's muscle size or strength.