Metformin does not improve insulin sensitivity over hypocaloric diets in women with polycystic ovary syndrome: a systematic review of 12 studies

To improve insulin action, most clinicians prescribe Metformin in patients with insulin resistance (IR). Women with polycystic ovary syndrome (PCOS), in which IR is an important physiopathological mechanism, treatment with Metformin and specialized diets have been suggested to reduce the patient’s IR. However, numerous studies have demonstrated conflicting results with respect to supplementing a diet with Metformin. Therefore, we conducted a meta-analysis to determine if Metformin provides a benefit in conjunction with hypocaloric diets to improve insulin sensitivity in PCOS women. PubMed, SCOPUS, LILACS, and EBSCO databases and retrieved studies’ bibliographies were searched for prospective studies that investigated the effect between Metformin and hypocaloric diets in PCOS women until April 2020. Pre- and post-intervention values for fasting plasma glucose (FPG), fasting plasma insulin (FPI), and IR indices (HOMA1-IR, ISI, and QUICKI) were extracted. Using Comprehensive Meta-Analysis software, the pooled standard difference in the means (SDM) and 95%CIs were calculated. 11 publications (12 studies) were selected. There was not a benefit of adding Metformin to a hypocaloric diet with respect to FPG (SDM= −0.17; 95%CI: −0.48–0.14, p = .28) and FPI (SDM = 0.16; 95%CI: −0.24–0.55, p = .45). None of the IR indices also demonstrated any benefit of using Metformin when a diet intervention was implemented (HOMA1-IR: SDM = 0.28; 95%CI: −0.27–0.84, p = .315; ISI: SDM = 0.344; 95%CI: −0.17–0.85, p = .186; QUICKI: SDM= −0.01; 95%CI: −0.42–0.41, p = .968). Here, we determined that adding Metformin to hypocaloric diets did not improve serum glucose or insulin concentrations as well as IR in PCOS women.