The incidence of obesity has dramatically increased during the last three decades, leading to a significant increase of obesity-related morbidity, including type 2 diabetes mellitus (T2DM) that is characterized by resistance of target tissues to insulin action. T2DM obese patients may be treated by medications or by bariatric surgery. Both alternatives have limitations due to incomplete resolution of the diseases, high cost or potential procedural related morbidity. An increasing body of evidence points to a role of the enteric microbiota in the pathogenesis of obesity-related insulin resistance. In addition to that, the gut microbiota is directly affected by the diet composition. Studies in T2DM mice carrying human gut germs, demonstrated special interactions between the gut microbiota and the host, creating a typical microbiota composition which changes significantly following diet change from a western diet, rich with sugar, to a vegetarian diet rich with fibers. This rapid alternations in the microbiota composition has also shown in humans, after changing from western to high fiber diet. A change in diet life style may lead to an improvement in T2DM symptoms such as decrease in visceral adipose tissue.