Consumption of dietary fiber at the recommended average intake of 25 g per day was associated with lower risks of developing symptomatic knee osteoarthritis and moderate or severe knee pain over 4-8 years in two separate analyses of Osteoarthritis Initiative participants conducted by investigators at Boston University.
The studies are the first to describe an association between total dietary fiber and lower risk of symptomatic OA and pain worsening in the knee, as well as a lower risk of moderate and severe pain patterns. The lowered risks were partially mediated by body mass index (BMI) but persisted even after adjustment for the variable.
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In both studies, the investigators estimated dietary fiber intake by using a validated food frequency questionnaire at baseline that summed the fibers from grains, fruits and vegetables, and nuts and legumes.
Fiber and symptomatic knee OA
At the end of 4 years of follow-up, Dr. Dai and her colleagues identified 152 knees with incident radiographic OA (defined as a knee newly developing a Kellgren and Lawrence grade of 2 or higher), 869 knees with incident symptomatic OA (defined as new onset of both radiographic OA and a painful knee on most days in past month), and 1,964 knees with pain worsening as defined by an increase of at least 14% of the baseline Western Ontario and McMaster Universities (WOMAC) Index pain subscale score at each annual exam. This analysis excluded 540 people who were lost to follow-up and 205 who had invalid caloric intake recordings, leaving 4,051 in the study. The outcomes also excluded people with prevalent radiographic or symptomatic knee OA or knee pain worsening at baseline.
There was a significant trend for lower risk of both symptomatic OA (P less than .002) and pain worsening (P = .005) across four quartiles of daily total dietary fiber intake (mean of 9.1 g, 13 g, 16 g, and 21.9 g in quartiles 1-4). Quartile 4 daily intake was associated with a statistically significant 30% reduction (95% confidence interval, 6%-48%) in the odds of symptomatic knee OA and a 19% reduction (95% CI, 6%-29%) in the odds of pain worsening. Both comparisons were adjusted for age, sex, race, total energy intake, education, smoking status, physical activity, intake of other dietary factors (including polyunsaturated fat and other fats, vitamin C, vitamin D, vitamin E, vitamin K, dairy products, sweets, and soda), and nonsteroidal anti-inflammatory drug use (for the pain-worsening comparison).
Even though approximately 34% of the association between total fiber intake and symptomatic OA and 22% of the association between total fiber intake and pain worsening were mediated through reduced BMI, further adjustment of the comparisons for baseline BMI yielded similarly significant results.
The investigators found no associations between total dietary fiber intake and radiographic knee OA or for other fiber intake with either symptomatic or radiographic knee OA.
“The strongest protection was suggested at the highest quartile, which is in line with the current dietary guidelines for daily fiber intake. For older people [aged 51 years and older], for women it’s 22 g per day and for men it’s 28 g per day,” Dr. Dai said at the meeting.
Fiber and knee pain trajectories
Dr. Dai and her associates identified distinct, relatively homogeneous clusters of WOMAC pain trajectories over the 8-year study course in patients with and without radiographic knee OA at baseline in the Arthritis Care & Research study, and then examined their relationship to participants’ total dietary fiber intake, divided into quartiles (Arthritis Res Care. 2016; Nov 29. doi: 10.1002/acr.23158). The investigators found four pain trajectory patterns, including no pain (34.5%), mild pain (38.1%), moderate pain (21.2%), and severe pain (6.2%).
Individuals who consumed the most total fiber also had the highest representation in the no pain pattern (38.1%) and the lowest representation in the severe pain pattern (4.3%). A high total fiber intake was associated with lower risk of having a moderate or severe pain pattern when compared with those in the no pain trajectory (both P for trend less than .01). Intake of fiber in the highest quartile was associated with a 24% lower likelihood (95% CI, 7%-39%) of belonging to the moderate pain pattern and a 44% lower likelihood (95% CI, 2%-59%) of being in the severe pain pattern, compared with individuals in the lowest intake quartile.
The same four pain trajectory patterns existed in individuals with radiographic knee OA at baseline, but the proportions were shifted slightly lower for no pain (26.1%) and higher for severe pain (7.9%). There was an even greater effect magnitude for the association between dietary total fiber and moderate or severe pain pattern among individuals with radiographic knee OA at baseline. Similar results were found for participants without radiographic knee OA at baseline. The relationships between total dietary fiber intake and pain patterns were somewhat attenuated after adjustment for depression scores and BMI at baseline but still remained statistically significant.
In each of the comparisons and sensitivity analyses, the highest quartile of cereal grain fiber intake was also significant on its own in lowering risk for being in the moderate or severe pain trajectory patterns. However, no significant results were found for fiber from fruits and vegetables or from nuts and legumes.
The studies were supported by grants from the National Institutes of Health. None of the authors had conflicts of interest to disclose.