Can you help explain something to me? Both my brother and I are significantly overweight (more than 100 pounds). He has terrible knee arthritis, which his doctor insists is because he is fat. I am even heavier than he is and I don’t have any knee pain. Why the difference between us?

Although obesity is a known, direct factor in joint arthritis, osteoarthritis (OA) is considered a multifactorial disease. There’s more than meets the eye on this one. In other words, many factors contribute to the damage and destruction of the joint that leads to arthritis.

For example, increasing age, sex (female), family history, race, previous injury, and lifestyle are all known risk factors for osteoarthritis (OA). Of all those risk factors, only obesity is considered modifiable (in other words, a risk factor you can do something about).

Though you share the same family history with your brother, you may not share the same personal history (e.g., past injuries) or even lifestyles. Exercise is known to help keep the joints lubricated and helps combat arthritic changes. Even being overweight, if you have a regular exercise routine, you may be able to hold off some of the arthritic changes that develop over time.

Obesity does, in fact, cause local biomechanical changes in the joint reducing shock absorbing ability and increasing load and force on the joint cartilage. Eventually the joint starts to break down. It is possible to have changes present that even show up on X-rays but no symptoms. Without an X-ray to know for sure, this could be your situation.

But even if nothing shows up on an X-ray you should be aware that fat cells (referred to as adipose tissue) also activate inflammation that is system-wide (throughout the entire body). This low-grade inflammation has a direct and pathologic effect on the musculoskeletal system (especially bone and cartilage). Fat is not just a store house of energy. It is also a very active endocrine (hormone producing) gland. Blood tests confirm that this is the case with elevated levels of inflammatory markers measured in obese people.

Scientists haven’t fully unraveled how obesity, systemic inflammation, and joint changes are all connected. But they are finding out more and more each day that may eventually help find a drug to prevent or at least manage osteoarthritis. This proinflammatory state of the obese body is also suspected as a contributing cause of hypertension, insulin resistance, and high cholesterol levels.

If you are overweight to the point of being considered obese, you know that weight loss isn’t easy. Many health care professionals recommend education to prevent weight gain first. But for those whose body mass index (BMI) indicates they are already past ‘normal’ and in the overweight or obese zone, weight loss is still advised.

Strategies for successful weight loss include diet and exercise, behavioral counseling and incentive programs, and/or possibly bariatric surgery. Slow, gradual, but steady weight loss is always preferred because maintaining weight loss is just as challenging as losing the weight in the first place. Negative side effects of bariatric surgery (e.g., decreased bone mass, increased risk of bone fractures, failure with weight gain) make this approach less desirable.

Don’t wait until you start to experience joint pain. Talk with your doctor soon and get on a plan that can work for you to change your diet, lifestyle, and body mass index. Encourage your brother to do the same. In the long-run, you will both benefit in more ways than one.