This is a randomized clinical trial, aimed to analyse the effects of a potentially anti-inflammatory nutritional intervention in disease assessment parameters, inflammatory markers, and quality of life of Fibromyalgia patients. Patients in the intervention group will adopt an anti-inflammatory diet and a diet with a low ingestion of fermentable oligo-, di- and monosaccharides, and polyols (FODMAPs), for a 3 months period. Group control will adopt a diet based on general recommendations for healthy eating in accordance with the World Health Organization.

The presence of low grade intestinal inflammation has been reported in Fibromyalgia (FM) patients. Other studies associate the persistence of symptoms described in FM to possible alterations of the intestinal microbiota composition, i.e. dysbiosis, with consequent existence of Small Intestinal Bacterial Overgrowth (SIBO). A sample of 100 female patients diagnosed with FM, followed-up at Portuguese Rheumathology Institute in Lisbon, will be distributed randomly in two groups. Group 1 will adopt an anti-inflammatory diet, which is characterized by the exemption of the intake of potentially inflammatory foods, namely gluten, dairy and ultra-processed foods, over a consecutive period of 3 months. During the first month, a low FODMAPs diet will be implemented, along with the anti-inflammatory diet, followed by the reintroduction of all fruits and vegetables over a consecutive period of 2 months, for a total of 3 months of intervention. Group 2 will adopt a diet based on general recommendations for healthy eating in accordance with the World Health Organization. The Ethics Committee of the Portuguese Institute of Rheumathology approved this intervention study.

The results of this study are expected to determine whether a change in patient nutrition helps to alleviate symptoms, which would optimize medical intervention.

Inclusion Criteria:

• Diagnosis of FM performed by the physician, according to the Rome III criteria of the American College of Rheumatology, revised in 2010;
• Ability to read and sign the Informed Consent;
• Stable dose therapy within 4 weeks before study start.

Exclusion Criteria:

• Patients with pathologies that prevent the follow-up of the given dietary protocol;
• Patients currently undergoing lactation or pregnancy;
• Prior or current clinical history of abuse of drug or other substances;
• Change of therapy during the intervention period;
• Presence of other inflammatory diseases;
• Uncontrolled medical conditions (eg. Diabetes Mellitus, decompensated heart disease, renal failure, neoplastic diseases, liver diseases).