A diet high in fat, especially saturated fat, may speed up the progression of knee osteoarthritis (OA), whereas eating greater amounts unsaturated fat might slow it down, according to researchers at Brigham and Women’s Hospital in Boston. Their study, published recently in Arthritis Care & Research, is one of the first to look at the effect of diet on the rate of OA progression. The researchers say they undertook the study because diet plays a role in the development of many chronic diseases, including diabetes, cancer and cardiovascular disease, and they suspected it might also be involved in osteoarthritis.
Lead author Bing Lu, MD, and colleagues followed more than 2,000 patients with knee OA who participated in a large National Institutes of Health osteoarthritis study. The participants filled out diet questionnaires at the beginning of the study and then at 12-month intervals for four years. These indicated how often they had eaten certain foods, including which types of fats, during the previous year. Disease progression was measured using X-rays that showed the amount of joint space in the knee. (Joint space is the area between the bones in a joint; loss of the cartilage that caps the bone ends makes the space more narrow, a key feature of OA.)
After taking into account other factors that might cause structural changes in the knee (such as age, weight, smoking, physical activity and knee injury or surgery), the researchers found that participants in the group that ate the most saturated fat (the type found in red meat, butter, cheese, lard and many processed foods) had the most joint space narrowing, indicating loss of cartilage and OA progression. The degree of narrowing increased with the amount of fat consumed: people who ate less saturated fat lost 25 millimeters (mm) of joint space over four years; those eating the most lost 37 mm.
On the other hand, participants who ate a diet high in unsaturated fats (found in foods such as vegetable oils, nuts and cold water fish) lost substantially less joint space than those who ate the least.
The researchers think these results reflect the ability of some fats to cause inflammation and others to tamp it down. Previous research has found that certain unsaturated fats, especially those found in olive oil, avocados, salmon, walnuts and flax seeds, are anti-inflammatory and might help prevent joint damage (other unsaturated fats, confusingly, may cause inflammation if eaten in disproportionate amounts).
Inflammation and Fat
OA is increasingly thought of, in part, as an inflammatory disease rather than one in which cartilage simply wears out from age or overuse. Synovitis – inflammation of the lining inside the joint capsule, the soft tissue that encloses a joint – is known to contribute to cartilage loss. Because saturated fats are inflammatory, it makes sense they could promote disease progression. But since this is an observational study, it identified associations between OA progression and dietary fats, but isn’t able to prove that eating more saturated fats (compared to eating more unsaturated fats) causes OA to progress faster.
David Felson, MD, a rheumatologist and professor at Boston University Medical Center, who wasn’t involved in the study, says the idea of making dietary changes to control osteoarthritis has real promise. Although Dr. Felson, an expert in OA research and population studies, thinks the current study is very good, he also points out its limitations. For example, he says standard food questionnaires are relatively limited and therefore not a particularly good measure of dietary quality. For one thing, researchers weren’t able to distinguish between unsaturated fats that are known to cause inflammation (such as soybean, corn and cottonseed oils) and those, like olive oil, that don’t. Still, the general trend was clear: saturated fats lead to more joint space loss than unsaturated ones.
He also thinks the researchers focused too much on structural changes in the knee. “Structural changes aren’t terribly important to patients; it’s more important to relieve pain,” he says. “Furthermore, joint space loss doesn’t necessarily equate well with cartilage loss and disease progression or with symptoms. [But], eating more unsaturated fatty acids and fewer saturated fats is a good dietary choice for many reasons, and if it helps with osteoarthritis, that’s just another reason to do it.”
Linda Rath for the Arthritis Foundation