High Saturated Fat Diet Bad for Knee OA
Weight loss and exercise are proven tools for managing knee osteoarthritis (OA). According to new research, having a diet high in fat, particularly saturated fatty acids (SFA), could worsen the rate of OA progression. By contrast, consuming high amounts of unsaturated fatty acids, like monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA), could have the opposite effect, actually slowing progression of the disease.
The study, published online in Arthritis Care & Research, is the first of its kind to draw an association between dietary fat content and radiological OA progression in a large patient group.1 While these possible dietary effects on OA progression are still being understood, physicians should encourage OA patients to manage their fat intake while exercising and losing weight.
The study was conducted as part of the Osteoarthritis Initiative, an international research effort sponsored by the National Institutes of Health. A total of 2,092 patients, who had been diagnosed with knee OA, submitted information about their diets through the Block Brief Food Frequency Questionnaire.
To assess radiological progression of the disease, researchers measured patients for their quantitative joint space width (JSW) between the medial femur and tibia of the knee, based on fixed-flexion posterior-anterior radiographs. Using linear mixed models, they looked to see if any associations existed between dietary fat and JSW loss over time.
“We observed significant positive relationships of total fat and saturated fatty acids (SFA) intakes with JSW loss,” the authors reported. As they assessed patients annually over the 48-month span of the study, data revealed the higher the fat intake, the worse the radiological progression—a dose-response relationship between fat/SFA intake and JSW.
Splitting patients into quartiles from the lowest total fat intake to the highest, JSW over 48 months progressively worsened in relation, by 0.26 mm, 0.27 mm, 0.31 mm, and 0.35 mm respectively (P = 0.02). Similar results were found when measuring only SFA intake – based on the lowest quartile SFA intake to the greatest, joint space narrowing progressed by 0.25 mm, 0.26 mm, 0.33 mm, and 0.37 mm, respectively (P < 0.01). (See Tables)
Researchers also reported that after adjusting for covariates, they found “a significant positive association between SFA intake and risk of OA progression,” which was consistent with the joint space analysis (see table).
However, while high fat intake was found to be positively related to OA progression, the researchers found the association was not statistically significant (P = 0.29).
Mono- and Poly-Unsaturated Fats Slow OA Progression
By contrast, higher intakes of a MUFA and PUFA appeared to slow the progression of radiological OA. For patients in the top quartile of consuming mono-unsaturated fats, they showed a 25% reduced risk of OA progression over those in the lowest quartile (P =0.05). Having a higher poly-unsaturated fat intake also appeared to have a great effect on slowing OA progression (see table).
Having a higher ratio of PUFA to SFA also associated with a reduced loss of joint space width. This carried over to OA progression as well, where there was an inverse relationship found between the PUFA/SFA ratio and the risk of OA progression (P = 0.01).
Dietary Fat Intake: How Does it Affect Knee OA Progression?
"Our findings add to the literature, showing a positive association of dietary saturated fat with knee OA progression, and potential protective effects of dietary PUFA and MUFA against knee OA progression," the authors wrote.
The data did also show that a higher MUFA intake associated with a lower joint space narrowing (and vice versa) although the trend was not statistically significant. Researchers also did not find any meaningful interactions between dietary fat intake and other variables, like age, sex, BMI, and smoking status.
While it is still difficult to explain how dietary fat intake can impact the progression of a disease like knee OA, it could be conceivable dietary content impacts OA disease progression, the researchers said. "Although the potential mechanisms linking dietary PUFA and OA are unknown, there is consistent evidence that PUFAs are directly linked to inflammation via their role as precursors for a family of compounds known as eicosanoids."
Low-energy, formula-based diet programs have been shown to reduce OA symptoms2, even though no measurable effect has been found on bone marrow lesions.3 Indeed, the National Institutes of Health’s (NIH) guidelines recommend a calorie-restricted approach to dieting.4 But besides the “calories in, calories out” approach, little research has gone into how diet composition could affect disease progression.
Obviously, proper nutrient intake is significant to cultivating a healthy diet for patients, like for women who may be at risk of osteoporosis.4 But recent research has explored a beneficial effect from supplementing exercise with a “Mediterranean diet,” – heavy on monounsaturated fatty acids mainly from consuming lots of olive oil.5
Limitations to Consider
There are also questions concerning the validity of the findings featured in the new study published in Arthritis Care & Research. At baseline, those in the highest quartile of fat consumption were demographically young, non-Hispanic black, poorly educated, smokers, and exhibiting depressive symptoms – all of which could be possible confounding factors.
It is possible obesity and weight change could have been intermediating factors that played a role in linking fat intake and OA outcomes over the course of the study’s 4-year period. The fact that the study excluded any patients with severe OA may have been impactful on the data, as well.
“Replication of these novel findings in other prospective studies are needed to confirm if reduction in SFA intake and increase in unsaturated fat intake lead to delayed knee OA progression,” the authors concluded.
This study was supported by the National Heart, Lung, and Blood Institute. The authors of the study reported no relevant conflicts of interest.