Around 20-30% of Fibromyalgia patients modify their dietary habits after diagnosis, including avoiding certain food groups such as cereals. In this systematic review, we used the PRISMA guidelines to select the main studies that have evaluated the effectiveness of restrictive diets, including elimination and vegetarian diets, in patients with Fibromyalgia. Data on vegetarian/vegan diets are more consistent than data on elimination diets due to higher quality and better results of the published studies. Although the results are favorable in most of the studies, their heterogenicity and the scarce and low quality of the evidence (small number of patients included, often non-randomized and uncontrolled studies and multiple confounding factors and biases) does not allow for a positive recommendation about these restrictive diets in Fibromyalgia patients. Several factors other than food restriction could influence the symptomatic and functional improvements observed after restrictive diets, such as the placebo effect, weight loss that often occurs, coexistence with gastrointestinal diseases and positive effects of unrestricted foods. We must advance more and improve in our knowledge of the effectiveness of restrictive diets and variables related to them before recommending them systematically to all patients with Fibromyalgia. Randomized, placebo-controlled trials with large sample sizes, longer follow-up periods and standardized outcome measures that explore predictors of dietary response are needed to better understand the relationship between Fibromyalgia and nutrition.
Keywords: diet; fibromyalgia; food; nutrition.