Swedish researchers found that RA sufferers who followed a vegan diet had fewer swollen joints and an increase in levels of antibodies that fight inflammation than those on a normal diet.
Patients on the vegan diet also reduced their risk of heart attack and stroke, due to lower BMI and lower levels of LDL cholesterol, say the papers.
It is estimated that there are around 350,000 people in the UK who suffer from RA.
What is the research?
The reports are based on a Swedish study that investigated the effects of a vegan diet on cholesterol levels, inflammation and RA symptoms.
Researchers randomly assigned 66 patients with active RA, who were aged 20-69 years, to a gluten-free vegan diet or a normal non-vegan diet for one year.
The 38 patients assigned to the vegan diet consumed mainly vegetables, nuts and fruits. But the eating plan also contained buckwheat, millet, corn, rice and sunflower seeds.
Protein accounted for 10 per cent of daily energy intake, carbohydrate 60 per cent and fat for 30 per cent.
The remaining 28 patients who followed a non-vegan diet ate equivalent proportions of protein, carbohydrate and fat, with saturated fat comprising no more than 10 per cent energy intake, and whole grains eaten where possible.
Patients were allowed to continue with RA medication, such as NSAIDs or anti-rheumatic therapy.
Measurements of BMI, LDL cholesterol and anti-phosphorylcholine - antibodies that can lower levels of the inflammatory marker phosphorylcholine - were taken at baseline, three months and at the end of the study.
The effects of the different diet regimes were compared and the researchers found those in the vegan group showed an increase in the number of anti-inflammatory antibodies.
The number of swollen joints among the vegan patients was reduced from an average of 5.3 to 4.3. No significant changes were seen in the normal diet group.
Those in the vegan group also showed reductions in weight, BMI and LDL cholesterol levels.
On average, BMI decreased from 24.1 to 22.7 in the vegan group, compared with a small decrease of 23.8 to 23.4 in the normal diet group.
What do the researchers say?
Lead researcher Professor Johan Frostegard, from the department of rheumatology at the Karolinska University Hospital in Stockholm, said: 'Our findings suggest a new mechanism by which the level of natural protective antibodies can be increased.
'They also show that diet can have effects on the immune system with implications for the incidence of disease.'
However, a bigger study group will be needed to discern which particular aspects of the diet helped the most, he said.
The researchers say further study is planned to investigate anti-phosphorylcholine antibodies for treating RA.
What do other researchers say?
Dr Peter Fisher, rheumatologist at the Royal London Homeopathic Hospital and spokesman for the charity Arthritis Research Campaign, said: 'Previous studies have shown that a vegan diet can help to reduce symptoms of RA.
'It is not surprising that LDL levels and BMI would be lowered by following a vegan diet.'
However, it is very difficult to follow a vegan diet and it could lead to malnutrition, warned Dr Fisher.
People on a vegan diet would miss out on vital nutrients including iron, calcium, vitamin B12 and omega-3, which are particularly important for RA patients, he said.
- Eating a vegan diet could help to reduce the symptoms of RA and lower the risk of heart attacks.
- Patients who followed a vegan diet were found to have a reduction in the number of swollen joints.
- Further studies are required to follow up this study.
- Following a vegan diet is difficult and can lead to malnutrition.