Rheumatoid arthritis, a medical condition in which the body's immune system attacks the lining of the joints, cannot be treated with a change in diet. Researchers arrived at this conclusion following a new review of 15 studies on the subject.
As rheumatoid arthritis progresses, the patient's joints can become swollen and stiff, reduced mobility.
Some of these symptoms can be relieved through available treatments, but no cure exists.
Many rheumatoid arthritis sufferers believe that a variety of special diets could ease their symptoms, which is why the reviewers felt it necessary to determine whether diet can be linked to the disease.
The review found little evidence that changing their diets made any significant difference.
"There are different theories behind certain diets. There are some reports showing that food allergy or intolerance is present or even common in RA patents," said lead review author Kare Hagen, a senior researcher at the National Resource Center for Rehabilitation in Rheumatology of the Diakonhjemmet Hospital in Oslo, Norway.
However, she added: "No body of evidence exists for dietary intervention for RA."
Reporting their work in the latest issue of The Cochrane Library, the reviewers said that one of the studies they looked at found that fasting followed by 13 months on a vegetarian diet might reduce pain by 1.89 percent on a scale of zero to 10, but had no effect on physical function or morning stiffness.
In another study, a 12-week Mediterranean diet-high in fruit, vegetables, cereals and legumes, fish and olive oil, and low in red meat-reduced pain by 14 percent, but had no effect on physical function or morning stiffness.
The reviewers further revealed that two studies looked at the use of an elemental diet, consisting of hypoallergenic, easy-to-digest food.
According to them, the diet, which is sometimes prescribed for patients with Crohn's disease, did not make any significant differences in pain, function or stiffness in participants with rheumatoid arthritis.
Even studies on vegan diets and elimination diets, which remove one or more food items from the diet to see if improvement occurs, were inconclusive.
The researchers also observed that the participants placed on a diet were twice as likely to drop out as those in control groups were.
They said that the participants who did change their diet lost more weight, up to six and a half pounds, without intending to do so - not necessarily a good thing for these people.
"As the authors conclude, there is not enough information to make a strong, scientifically based recommendation regarding use of dietary changes to control RA inflammation symptoms. One of the problems is that there are few well-done clinical studies that have investigated the influence of diet on RA inflammation and the studies that have been done differ from one another," said Mark Wenner, M.D., a professor at the University of Washington School of Medicine.
Still, added Wenner, diet does offer other benefits for related conditions for which RA patients are at increased risk.
"For example, attention to dietary and nutritional factors that lower risk for cardiovascular disease and osteoporosis is particularly valuable for RA patients," he added.
For him, the review confirmed the benefits of the Mediterranean diet, which he recommends as a healthy heart diet. While the improvement in rheumatoid arthritis generally is modest, he said, the Mediterranean diet poses little risk.