According to the present invention, a lipid metabolism improving agent containing hydrogen molecules that is in a liquid or gas state is provided. The lipid metabolism improving agent of the present invention comprises a liquid or gas containing at least hydrogen molecules. It may comprise a medium containing oxygen molecules. Further, such medium may comprise water, an aqueous solution, or a gas. The lipid metabolism improving agent has effects of suppressing body fat accumulation, arteriosclerosis, and the like.