The links between diet, obesity, exercise and arthritis have been the focus of much research attention, partly because arthritis is estimated to affect as many as 20% of adults in the US. One form of arthritis, called osteoarthritis, is characterized by inflammation, joint degeneration and development of osteophytes (bony outgrowths around joints), resulting in pain. Conventional wisdom may lead arthritis sufferers to avoid activity in order to minimize joint pain. But many cases of arthritis are associated with obesity and inactivity.

To address this conundrum, researchers from Duke University (Durham, NC) led by Farshid Guilak designed a study to test two hypotheses: first, that obesity resulting from consumption of a high-fat diet would encourage development of osteoarthritis in mice and second, that running-wheel activity would inhibit this development. The study included 20 male C57BL/6J mice, half of which were fed regular chow (with 13.5% of its calories coming from fat) and half of which were given a very high-fat diet (60% of calories coming from fat). Half the mice in each diet group were then given access to a running wheel during part of the study.

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Guilak's group assessed severity of osteoarthritis in the knee by histopathology and measured serum cytokine levels, body composition and insulin resistance in all the mice (Arthritis Rheum. doi:10.1002/art.3332; published online 27 September 2011). Mice on the high-fat diet gained weight rapidly; their percent body fat tripled relative to that of mice that received standard chow. They also had higher osteoarthritis scores and cytokine levels and had impaired glucose processing abilities relative to mice that ate regular chow. The data confirmed the study's first hypothesis, linking ingestion of a high-fat diet with obesity and osteoarthritis. Mice that used the running wheels, however, were protected from further arthritis progression. Even though their body weight, percent body fat and serum cytokine levels remained elevated, their arthritis scores were lower, co-expression of pro-inflammatory cytokines was disrupted and glucose tolerance improved. Overall, development of arthritis was slowed in obese mice that used running wheels, confirming the study's second hypothesis.

The study results suggest that although obesity contributes to the development of osteoarthritis, the increased load on joints resulting from obesity is not its sole cause. Furthermore, it seems that weight loss is not required, and reduction of physical activity is not desirable, to slow arthritis progression or relieve symptoms.