BackgroundPolycystic Ovary Syndrome (PCOS) is known as the most common endocrine disorder of women in reproductive ages. With the increasing prevalence of PCOS in different countries, the use of herbal medicine as an alternative treatment is growing in these patients. This study aimed to evaluate the effects of flaxseed powder supplementation on metabolic biomarkers of patients with PCOS.MethodsThis randomized open-labeled controlled clinical trial was conducted on 41 patients with PCOS. The participants were randomized to take either flaxseed powder (30 g/day) plus lifestyle modification or only lifestyle modification for 12 weeks. Anthropometric and biochemical evaluations were performed for all patients at the beginning and end of the study.ResultsThe flaxseed group showed a significant reduction in body weight, insulin concentration, Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), Triglycerides (TG), high-sensitivity C-Reactive Protein (hs-CRP), and leptin and an increase in Quantitative Insulin-Sensitivity Check Index (QUICKI), High Density Lipoprotein (HDL), and adiponectin compared to the baseline (p < 0.05). Flaxseed supplementation also led to a significant reduction in insulin concentration, HOMA-IR, TG, hs-CRP, Interleukin 6 (IL- 6), and leptin and an increase in QUICKI, HDL, and adiponectin compared to the control group (p < 0.05). No significant changes were observed in other parameters.ConclusionsFlaxseed supplementation plus lifestyle modification was more effective compared to lifestyle modification alone in biochemical and anthropometric variables in patients with PCOS.Trial registrationThe trial protocol was approved by the Ethics Board at Ahvaz Jundishapur University of Medical Sciences and was registered at Iranian Registry of Clinical Trials (code: IRCT20120704010181N11).