A plant-based diet may alleviate painful symptoms associated with rheumatoid arthritis (RA), according to a new review published in the journal Frontiers in Nutrition.

RA is an autoimmune disorder characterized by inflammation that causes pain and swelling. While genetic factors are important, studies show that lifestyle factors, including diet, play a role. Researchers with the Physicians Committee for Responsible Medicine reviewed clinical trials and observational studies and found strong and consistent evidence that a plant-based dietary pattern can reduce inflammation and improve symptoms associated with RA.

The study authors highlight four ways a plant-based diet may be effective:

1. Plant-based diets reduce inflammation. A 2015 study found that participants randomized to a two-month plant-based dietary intervention experienced reductions in inflammatory scores, when compared to those eating diets higher in fat and animal products. Other studies have found that diets high in fat and processed meat are associated with inflammatory markers, including C-reactive protein (CRP). Plant-based diets and high-fiber diets have been associated with lower CRP levels.

2. Plant-based diets reduce RA pain and swelling. A randomized clinical trial that looked at the effects of a low-fat vegan diet on people with moderate-to-severe RA found that after just four weeks on the diet, participants experienced significant improvements in morning stiffness, RA pain, joint tenderness, and joint swelling. The review authors suggest that plant-based diets are typically low in fat and high in fiber, which can reduce inflammation and decrease pain and swelling.

3. Plant-based diets are associated with a lower BMI. Studies show that excess body weight increases the risk for developing RA and decreases the likelihood of remission if RA is already present. A 2018 analysis found that RA patients who lost more than 5 kilograms of body weight were three times more likely to experience improvements than those who lost less than 5 kilograms. Plant-based diets have consistently proven to be effective for weight loss.

4. Plant-based diets promote healthy gut bacteria. Some studies suggest that the microbiome may play a key role in RA and inflammation. The authors note that high-fiber plant-based diets can alter the composition of gut bacteria and increase bacterial diversity, which is often lacking in RA patients.

“A plant-based diet comprised of fruits, vegetables, grains, and legumes may be tremendously helpful for those with rheumatoid arthritis,” says study co-author Hana Kahleova, MD, PhD, director of clinical research for the Physicians Committee. “This study offers hope that with a simple menu change, joint pain, swelling, and other painful symptoms may improve or even disappear.”

While more research is needed, the review adds to the evidence that diets rich in fruits, vegetables, whole grains, and legumes may be beneficial for autoimmune conditions. Other studies have found that a plant-based diet may be protective against hypothyroidism, hyperthyroidism, and multiple sclerosis.