Dietary Phytonutrients in Fibromyalgia: Integrating Mechanisms, Biomarkers, and Clinical Evidence-A Narrative Review

Background and Objectives: Fibromyalgia (FM) is associated with chronic pain, oxidative stress, low-grade inflammation, and disturbances in signalling along the gut-brain axis. These pathways may be modulated by plant-derived phytonutrients. This narrative review summarises mechanistic and clinical evidence on phytonutrient-based strategies in FM. Materials and Methods: Following SANRA guidelines, we searched PubMed, Web of Science, Scopus and ScienceDirect for human and relevant preclinical studies published between 2005 and October 2025 that evaluated phytonutrient-rich dietary patterns or isolated bioactives in relation to FM symptoms or underlying mechanisms. Results: There is a consistent association between FM and increased oxidative damage and reduced antioxidant defences. Adopting plant-based diets, particularly Mediterranean-type and low-FODMAP diets, has been linked to improvements in pain, fatigue, sleep, and gastrointestinal symptoms, as well as modest gains in quality of life. However, the effects on inflammatory markers are conflicting. Trials of selected bioactive compounds, such as coenzyme Q10, curcumin-based formulations, L-carnitine and certain probiotics, suggest beneficial effects on symptoms, whereas others show little or no effect. Studies of the microbiome indicate a loss of butyrate-producing bacteria and altered microbial metabolites. Early dietary or probiotic interventions may partially mitigate these changes to some extent. Preclinical studies have identified SIRT1 as a potential mediator, but there is a lack of human data. Reporting on safety, dosage and formulation is often inadequate. Conclusions: Given the narrative design of this review and the methodological heterogeneity of the included studies, the overall certainty of the evidence cannot be formally graded and should be regarded as limited and heterogeneous. Nevertheless, current data supports phytonutrient-rich, food-based approaches as adjuncts rather than alternatives to standard FM care. Well-designed randomised trials with standardised outcomes and reporting of dose, formulation and relevant biomarkers are needed to identify the most effective strategies and the patient subgroups most likely to benefit.