Fruit and whole-grain cereals are excellent sources of fiber.
Osteoarthritis (OA) is the most common type of arthritis, affecting more than 30 million U.S. adults. Worldwide, it is estimated that almost 10 percent of men and 18 percent of women aged 60 and over live with symptomatic OA.
Also known as "wear and tear" arthritis, the joint disorder affects elders in particular, with women over the age of 50 being the most likely to develop the condition.
New research - published in the journal Annals of the Rheumatic Diseases - investigates the link between a diet rich in fiber and the risk of developing knee OA.
The new study consists of a meta-analysis examining two long-term studies on the benefits of a fiber-rich diet. The study was a collaborative effort between researchers from Tufts University in Boston, MA, and the University of Manchester in the United Kingdom.
The first author of the study is Dr. Zhaoli Dai, of the Human Nutrition Research Center on Aging and Friedman School of Nutrition Science and Policy at Tufts University.
Good sources of fiber include nuts, legumes, fruit, whole grains, and non-starchy vegetables.
Studying the link between OA and fiber intake
The studies included in the new research were the Osteoarthritis Initiative (OAI) (which examined a total of 4,796 participants) and the Framingham Offspring Osteoarthritis Study (which comprised 1,268 participants).
The researchers determined the participants' fiber intake at the beginning of the study using a food frequency questionnaire. They also assessed incident radiographic OA and symptomatic OA - that is, they used X-rays to determine OA and recorded OA symptoms, the most common of which include knee pain, stiffness, and swelling.
The participants were clinically followed every year for 48 months as part of the OAI study, and they were evaluated after 9 years as part of the Framingham study.
Researchers also collected clinical data on other factors that may have influenced the results, including knee injury, medication, lifestyle, alcohol consumption, and physical exercise.
High intake of fiber lowers risk of OA by 30 and 61 percent
Patients consumed an average of 15 grams of fiber every day in the OAI study, and 19 daily grams in the Framingham study.
In the OAI study, at the end of the 4-year period, a total of 869 knees had OA symptoms, and 152 showed signs of OA on the X-ray. Additionally, the pain got worse in 1,964 knees.
In the Framingham study, at the end of the 9-year period, 143 knees presented OA symptoms, and 175 showed signs of OA on the X-ray.
Overall, the statistical analysis indicated that a higher intake of fiber correlated with a lower risk of painful OA.
Participants were divided into fourths, or quartiles, with the top quartile being compared with the lowest quartile in terms of fiber intake.
The participants who consumed the most fiber had a 30 percent lower risk of OA in the OAI cohort, and a 61 percent lower risk of OA in the Framingham cohort, compared with those who consumed the least fiber.
Furthermore, the study revealed that consuming more fiber in general, as well as more cereal fiber in particular, significantly reduced the risk of the knee pain getting worse. However, as the study is observational, it cannot establish causality.
Dr. Dai and colleagues conclude:
"Findings from two longitudinal studies consistently showed that higher total fiber intake was related to a lower risk of [symptomatic OA], while the relation to [incident radiographic OA] was unclear."