This study aimed to investigate the effects of infant feces-derived Bifidobacterium breve CCFM1078 on rheumatoid cachexia (RC). Twenty-four female Wistar rats were assigned to 3 groups: CON group (normal saline by gavage), CIA group (collagen-induced arthritis (CIA), normal saline by gavage), and CCFM1078 group (CIA, 3 × 10⁹ CFU/(rat·day) B.breve CCFM1078 gavage). The results demonstrated that B. breve CCFM1078 not only improved skeletal muscle function in CIA rats, but also modulated the gut microbiota, skeletal muscle metabolism and hormone levels, reduced inflammation in the knee joint and skeletal muscles, decreased activity of the nuclear factor κB (NF-κB) inflammatory signaling pathway, enhanced the insulin receptor substrate 1 (IRS1)/phosphatidylinositol 3-kinase/protein kinase (PI3K/Akt) signaling pathway, promoted skeletal muscle differentiation, and maintained skeletal muscle fiber diameter, consequently slowing down the progression of RC. These findings suggested that B. breve CCFM1078 may have a beneficial role as part of a dietary intervention for RC, enhancing overall therapeutic effects.