The present invention relates to prevention and treatment of obesity and obesity-related metabolic syndrome, particularly to prevention and treatment of obesity by change of intestinal flora. In the present invention, it was ascertained that the characteristics of intestinal bacteria are transformed by administration of a microorganism preparation which improves free fatty acid absorption by the bacteria, and free fatty acid absorption in the gastrointestinal tract is thereby decreased by introduction thereof The present invention provides a method for preventing and treating obesity and obesity-related metabolic syndrome, a pharmaceutical composition and diet supplement for prevention and treatment thereof, and modified probiotic strains usable for such purposes on the basis of these experimental results. The present invention shows a weight loss effect equal to that of orlistat which is most widely used as an anti-obesity therapeutic agent. The present invention shows that the absorption of fatty acids in the gastrointestinal tract is blocked by improving the characteristics of intestinal bacteria and transplanting them, thereby enabling the treatment of obesity.
