The Effect of a Plant-based Diet on the Active Rheumatoid Arthritis Activity.

The increase in autoimmune diseases in Western countries has been linked to environmental factors, and diet is considered a modifier of rheumatoid arthritis (RA). A high-fat diet promotes systemic inflammation and alters the microbiome. Certain bacteria in the intestinal microbiota generate proinflammatory metabolites from components of red meat, eggs, and dairy products. However, fruits and vegetables can modulate the gut microbiota and have been associated with reduced inflammation in RA patients. The aim of this study is to determine the changes in RA activity associated with plant-based dietary modifications. The study will evaluate men and women aged 18 years and older with low, moderate, or severe RA activity, and the intervention will involve an individualized, isocaloric plant-based diet for 14 days. The 28-joint disease activity score index and c-reactive protein (DAS 28-PCR) will be used to determine disease severity, in addition to analyzing the expression of inflammatory cytokines and microRNAs associated with RA.

The recent increase in autoimmune diseases in Western countries has seen environmental factors as important triggers of disease, as the genetic basis in affected populations has remained apparently constant. Diet has been seen as a modifying factor for several years in rheumatoid arthritis (RA).

A high-fat diet alters the structure of the microbiome even in the absence of obesity. However, it is also an important factor that promotes excessive accumulation of white adipose tissue (WAT) and systemic inflammation. For several decades, it has been evaluated how the intestinal microbiome participates in the metabolism of some components of the diet and has the potential to modify the circulating proinflammatory or anti-inflammatory mediators. In the context of patients with RA, it has been found that the bacterium Prevotella Copri, found in greater proportion in patients with newly diagnosed rheumatoid arthritis, generates a pro-inflammatory metabolite called N-trimethylamine oxide derived from choline and carnitine present in red meat, eggs, and dairy products. On the other hand, fruits and vegetables can modulate the gut microbiota through dietary fiber. The proportion of anti-inflammatory bacteria Faecalibacterium Prausnitzii, is higher in vegetarian diets, which has been seen in fecal flora as beneficial in patients with RA associated with reduced inflammation.

For several years, it has been reported in the literature that patients associate certain foods with increased or improved symptoms of the disease. However, a diet that combines several suggested strategies to reduce inflammation may represent a more significant intervention than just including specific foods in the diet. The role of the plant-based diet on RA activity has not been fully elucidated.

Based on this background, the objective of this work will be to determine the decrease in RA activity associated with plant-based dietary modifications. To carry out this protocol, women and men aged 18 and over with low, moderate, or severe rheumatoid arthritis activity will be evaluated. For dietary intervention, at the beginning of treatment, patients will be evaluated anthropometrically (weight, height, body mass index, waist and hip circumference, waist-hip index, percentage of total fat, visceral fat, and percentage of muscle), and a basal blood sample will be taken at the end of the procedure. The kilocalories typically consumed will be calculated through a 24-hour reminder to set your personalized meal plan. A dietary table will be made with the following distribution of macronutrients: carbohydrates 57%, protein 18%, and lipids 25%. Subsequently, the food will be distributed in an equivalent distribution table, complying with the kilocalories and the percentage of macronutrients established. The consumption of food of animal origin will be reduced, replacing this protein with vegetable protein.

The intervention will be carried out for 15 days, the menu will be modified at 7 days of intervention following the same specifications. At the end of the treatment, the patients will be evaluated under the same anthropometric conditions, and blood sampling for laboratory analyses. To determine the severity of the pathology, the DAS (Disease Activity Score) index will be used. A scale that measures RA activity. This scale influences the tumor and painful joint count on 28 joints, the rate of globular sedimentation (GSR), and the evaluation of the disease by the patient. This scale has a value of 0.0 to 9.4.

Eligibility Criteria:
Inclusion Criteria:

* Subjects over 18 years of age.
* Established diagnosis of rheumatoid arthritis according to American College Rheumatoid (ACR) 1987 or ACR/European Alliance of Associations for Rheumatology (EULAR) 2010 criteria.
* Disease activity according to DAS 28 (defined as all \> 2.6).

Exclusion Criteria:

* Systemic autoimmune superposition syndrome (with the exception of: fibromyalgia, thyroid pathology, Type 1 Diabetes Mellitus, syndrome Sjögren and antiphospholipid syndrome)
* Patients on treatment with coumarins
* Patients with cancer, chronic hepatitis, HIV, pregnancy
* Weight variations associated with diet in last 6 months