An anti-obesity agent or a glucose tolerance-ameliorating agent containing a bacterium belonging to the genus Bifidobacterium as an active ingredient, wherein the bacterium belonging to the genus Bifidobacterium exhibits a conversion rate from linoleic acid into conjugated linoleic acid of not more than 10%. The present invention is able to provide an anti-obesity agent and a glucose tolerance-ameliorating agent that are effective for the prevention or treatment of obesity or the amelioration of glucose tolerance and also exhibit superior safety, as well as providing foods or beverages containing these agents. Further, the present invention is also able to provide a bacterium of the genus Bifidobacterium, and in particular a Bifidobacterium breve, that is effective for the prevention or treatment of obesity or the amelioration of glucose tolerance and also exhibits superior safety, as well as providing a pharmaceutical composition containing this bacterium.