Researchers have found yet another benefit of a high-fiber diet: It is associated with a reduced risk for arthritis of the knee.

Knee osteoarthritis, which is common in aging populations, can be both painful and debilitating.

Researchers used data from two long-term observational studies, one with 4,796 subjects and the other with 1,268. The new analysis is in the Annals of the Rheumatic Diseases.

As fiber intake increased, the prevalence of arthritis decreased. In the larger study, those who ate the most fiber were 30 percent less likely to have knee osteoarthritis than those who ate the least, and in the smaller study, they were 61 percent less likely. The associations persisted even after controlling for age, sex, race, education, smoking, total calorie intake, physical activity, the intake of polyunsaturated fat and other dietary factors.

The mechanism is unclear, but fiber may reduce inflammation and help control weight. The average intake of fiber in the study was 15 grams a day, but the recommended level is 25 to 30 grams a day for most people.

“Increasing dietary fiber is one of the most economical ways to reduce the pain of knee osteoarthritis,” said the lead author, Zhaoli Dai, a postdoctoral fellow at Boston University. “And there are a lot of other benefits as well — reduced weight, reduced cardiovascular risk, reduced diabetes risk.”