DURHAM — The link between obesity and osteoarthritis has long been attributed to excess weight wearing out joints, but diet may be equally or even more important in explaining the severity of osteoarthritis in mice, according to a study by Duke researchers published Friday.
Mice fed a high-fat diet supplemented with omega 3 fatty acids had healthier joints and recovered from wounds faster than mice fed a high-fat diet without the supplement, according to the Duke researchers.
“Our results suggest that dietary factors play a more significant role than mechanical factors in the link between obesity and osteoarthritis,” says Farshid Guilak, professor of orthopaedic surgery at Duke and the senior author of the study published in the Annals of the Rheumatic Diseases.
Osteoarthritis is a degenerative disease in which joint tissues break down and cause stiffness and pain. It’s the most common form of arthritis in the U.S., according to the Centers for Disease Control.
The strong association between obesity and osteoarthritis led to the assumption that excess weight stress on joints causes arthritis, though that doesn’t explain why arthritis is also found in non-weight bearing joints like those in the hands.
Previous research conducted by Guilak and his colleagues discovered diet may play a role in osteoarthritis by finding an association between the lack of the appetite hormone leptin and the occurrence of arthritis in mice. That finding led researchers to study the effect of both diet and obesity by comparing the severity of osteoarthritis in mice fed different diets.
Mice were fed one of three high-fat diets: one high in saturated fat; one rich in omega 6 fatty acids, or one with an omega 6 fatty acids supplemented with a small amount of omega 3 fatty acids commonly associated with fish oil. Researchers then artificially induced osteoarthritis through surgical injury of the left knee joint.
A surprising effect
Dietary fatty acids influenced the severity of osteoarthritis independent of body weight, says Chia Lung Wu, a biomedical engineering graduate student in the Duke Orthopaedic Research Laboratories and the study’s lead author.
Mice fed the unhealthy high-fat diets developed severe arthritis and higher joint inflammation compared to mice fed a regular diet or a high-fat diet supplemented with omega 3 fatty acids. Omega 3 fatty acids also exhibit anti-inflammatory properties, potentially explaining the link between the supplemented diet and less severe osteoarthritis.
Still, Guilak said, “We were very surprised that this dietary supplement of omega 3’s actually had such a large effect.”
High concentrations of saturated and omega 6 polyunsaturated fatty acids characterize the typical Western diet. Saturated fats occur in foods like cheese and meat, while corn, soybean and other nut oils contain high levels of omega 6 fatty acids.
The study takes an important step in understanding the pathways to osteoarthritis, according to Steve Messier, professor of health and exercise science and director of J.B. Snow Biomechanics Lab at Wake Forest University.
“You can see the relevance for this down the road to human beings,” Messier said.
Osteoarthritis affects more than 33 percent of adults over the age of 65 and is one of the leading causes of disability in adults. There is no cure, but treatments can slow the progression of the disease and alleviate symptoms.
Guilak believes a clinical study is needed to determine whether diet exhibits similar effects on osteoarthritis in humans.
“The data is very supportive of going to that next step,” he said.