The study will be conducted at the Fibromyalgia Clinic (Rheumatology Unit, Sourasky Medical Center). For each patient/volunteer, all assessments (BMI, questionnaires, blood test) will be performed at a single visit. The principal investigator (K.A.) will enroll eligible and willing participants from among the female patients treated at the clinic. Eligible patients will receive a description of what is entailed in participating in the study. Suitable and willing patients will sign the informed consent form and then 1) undergo venopuncture [10 ml venous blood] and 2) complete questionnaires, with the guidance of an investigator. Data and blood samples obtained from patients will be de-identified (recoded) and stored in Clinical Research Forms (CRFs) and in test-tubes at -70oC, respectively. Blood samples will undergo fatty acid analysis (see laboratory methods) and magnesium concentration. Serum will be stored and kept for potential future analysis (e.g. for pro-inflammatory cytokines), but will not be subjected to genetic analysis.