Modulation of Gut Bacterial and Fungal Microbiota in Fibromyalgia Patients Following a Carb-Free Oloproteic Diet: Evidence for Candida Suppression and Symptom Improvement

Fibromyalgia (FM) is a complex chronic syndrome characterized by widespread pain, fatigue, and gastrointestinal complaints. Clinical observations and preliminary metabolomic data suggest a possible link between symptom severity and intestinal dysbiosis, including fungal overgrowth. This study investigates whether a carb-free oloproteic diet can beneficially modulate the gut microbiota in FM patients. Thirty-four female patients with diagnosed FM were enrolled in a controlled, parallel-arm nutritional intervention. Group FM1 (n = 22) followed a 45-day carb-free oloproteic diet followed by a 45-day low-glycemic (LOGI) diet. Group FM2 (n = 12) received a continuous LOGI diet for 90 days. They were collected at baseline (T0), after 45 days (T45), and at 90 days (T90). Microbial profiles were analyzed by 16S and 18S rRNA gene sequencing to assess bacterial and fungal composition. In FM1, the oloproteic phase led to a marked reduction in fungal abundance (Ascomycota) and an increase in butyrate-producing bacteria such as Faecalibacterium and Roseburia. These changes were partially reversed after the LOGI phase. In FM2, no significant microbiota shifts were observed. Clinical improvements paralleled microbiota modulation only in FM1. The carb-free oloproteic diet may support gut microbial rebalancing in FM, particularly through transient suppression of fungal overgrowth. These findings support further investigation into nutritional strategies targeting dysbiosis in FM management.