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Protecting the Knees from Osteoarthritis

In a new study, losing weight slowed degeneration of cartilage for people who are obese, but only with dietary changes, not exercise alone.

Jason Socrates Bardi, Editor-in-Chief
Fri, 01/05/2018


People who are obese and seek to lose weight to protect their knees against the irreversible, degenerative and painful effects of osteoarthritis should carefully consider their weight-loss strategy, according to the results of a new study.

The research looked at 760 men and women from a nationwide study called the Osteoarthritis Initiative. It suggests that people who were obese and lost weight were able to slow the degeneration of their knee cartilage, but only if they lost weight through dietary changes or diet combined with exercise -- not through exercise alone.

"It is best to either lose weight through diet or the combination of diet and exercise," said Alexandra Gersing, a radiologist now at the Technical University of Munich who led the study and presented the results late last year at the Radiological Society of North America meeting in Chicago.

Prior to moving to the Technical University, Gersing was a radiologist at the University of California, San Francisco, where she and her colleagues conducted the study.

"This type of data will help to inform exercise or weight-loss strategies," said Tim Mosher, a musculoskeletal radiologist at Pennsylvania State University, who was not involved in the research.

Bad knees, like bald tires

Osteoarthritis, also known as degenerative joint disease, is the most common form of arthritis and a major cause of disability in adults. The main physiological player in the disease is cartilage, which wears out over time just as the tires on your car wear out. Damage to the knee from sports injuries or accidental fractures is known to hasten this degeneration, and obesity and lack of exercise are also known risk factors for osteoarthritis.

Conversely, weight loss is known to lessen the risk of osteoarthritis and to improve disease symptoms for those who already suffer from it. "If you are obese, the more [weight] you lose, the more it lessens your symptoms," Gersing said.

Because the damage to the knees is irreversible, slowing degeneration is seen as an important avenue for addressing osteoarthritis. Assessing the best ways to reach this goal was part of the motivation for the new study.

Half the study population lost weight and the other half did not. The study segmented the 380 people who did lose weight into three groups, based on whether they combined dietary changes and exercise, used exercise alone, or shed the pounds using only an altered diet. The researchers then quantified the progression of knee osteoarthritis in all the subjects with MRI, taking data at the beginning of the study and again after 48 and 96 months.

What they found was that in general people who lost weight had significantly less cartilage degeneration than the 380 people who were controls and saw no weight loss. But this outcome was only true for those who lost weight through dieting alone or dieting combined with exercise.

Those who lost weight through exercise alone lost just as much weight as their counterparts, but there was no benefit to their knees. They lost just as much cartilage as the controls.

One of the lessons of the study, Mosher said, is that people should not suddenly go from sitting on a couch to trying to run a marathon. Instead, he said, exercise should be regarded as a component of an overall weight-loss strategy -- something he said patients should discuss first with their primary physicians.

There are many other questions about the biology of osteoarthritis that still need to be understood, he added. Some studies have suggested inflammation in the knees may play a confounding role and may make people who are obese and lose weight still at higher risk for the degeneration associated with osteoarthritis. There are also theories that one's gait may play a role.

Over the longer term, said Mosher, more data are needed to understand the impact of exercise, types of exercise and patterns of exercise on human health -- especially for people who lead less active lifestyles.

Most of what we know about exercise comes from athletes, Mosher said. "Here we are looking at more natural lifestyles."


The author of this article formerly worked at UCSF Medical Center in a public information capacity and wrote occasionally about research in the radiology department.