Obesity is a major global health concern. Studies suggest that the gut microflora may play a role in protecting against obesity. Probiotics, including lactic acid bacteria and , have garnered attention for their potential in obesity prevention. However, the effects of -fermented products on obesity have not been thoroughly elucidated. , which exists in the gut of animals, is known to enhance lipid metabolism. During fermentation, it produces acetic acid, which has been reported to improve glucose tolerance and insulin resistance, and exhibit anti-obesity and anti-diabetic effects. Functional foods have been very popular around the world, and fermented milk is a good candidate for enrichment with probiotics. In this study, we aim to evaluate the beneficial effects of milks fermented with strains on energy metabolism and obesity prevention. Three strains (Bif-15, Bif-30, and Bif-39), isolated from newborn human feces, were assessed for their acetic acid production and viability in milk. These strains were used to ferment milk. Otsuka-Long-Evans Tokushima Fatty (OLETF) rats administered Bif-15-fermented milk showed significantly lower weight gain compared to those in the water group. The phosphorylation of AMPK was increased and the expression of lipogenic genes was suppressed in the liver of rats given Bif-15-fermented milk. Additionally, gene expression related to respiratory metabolism was significantly increased in the soleus muscle of rats given Bif-15-fermented milk. These findings suggest that milk fermented with the strain Bif-15 can improve lipid metabolism and suppress obesity.