Why is Weight Loss in Osteoarthritis Important?

A key message for those suffering from osteoarthritis is that any small reduction in your body weight is likely to reduce your pain and improve your function, particularly in the knee joint.  Being overweight is a significant risk factor for getting osteoarthritis in the first instance, contributing to just under 50 % of this risk in knee osteoarthritis. Other risk factors for knee osteoarthritis include injury or trauma to the knee joint (about 20 %) and occupational (seen more in manual workers).  

It is probably easier to understand how excessive body weight affects our weight bearing joints such as the hip or knee due to the extra stress this places on our lower limb joints. It is true that for every extra kilogram of weight we carry does result in about 4-5 kg of additional load going through our knee joint. Losing weight then will reduce this load on your knees and lower limb.

What intuitively may not make sense is that obesity or excessive weight is associated even in osteoarthritis of non-weight-bearing joints such as the hand.  One of the proposed reasons for the connection between hand osteoarthritis and our body weight is due to the relationship between adipose tissue and inflammation in your body.

Two reasons why intensive weight loss may help osteoarthritis pain and function:

(1)   A biomechanical benefit- this results in less stress on your joints when you lose weight

(2)    An anti-inflammatory effect- there is less inflammation or inflammatory markers circulating in your body that results in a reduction in your pain

A study done in 2013 by Messier [1] demonstrated the effect of weight loss on pain and function in knee osteoarthritis over an 18-month duration. It was found that even a small reduction in body weight resulted in significant pain reduction and improved function. It is generally recommended that people with osteoarthritis, particularly of the knee joint, aim to reduce their body weight by even as little as 5 %. This means if you are 100 kg, that even if you reduce your body weight by 5 kg, you should start to notice a reduction in pain.

There is a dose response to weight loss which simply means the more you lose, the greater the reduction in your pain levels. As a basic rule, a 5-10 % reduction in body weight should result in up to a 30-50 % reduction in your reported pain.  Combining weight loss and exercise together is more effective and does result in higher reductions in pain and improved function. A recent study by Messier [2] has shown that weight loss also seems to play a role in improving the bio-mechanics around the knee joint and reducing compressive or loading forces around the joint.

Many osteoarthritis programs and surgeons now strive for significant weight loss prior to having any joint replacement surgery. There are numerous reasons for this, the main being that reducing your weight prior to surgery may mean you may decide not to require a joint replacement as your pain becomes manageable. It is important to remember that 80 % of people report being satisfied 12 months following a joint replacement, so it is important you try all conservative treatments such as weight loss and exercise prior to contemplating any surgery even if this is only for a brief period of time.

Losing weight and exercising the right way is never easy. It is important you do seek professional advice from a dietician as most peope who are overweight or obese do require special consideration about calorie intake and use of meal replacements such as shakes. Seeking professional advice and support from a physiotherapist about exercising for osteoarthritis is important as well. Programs such as GLA:D and PEAK are really good osteoarthritis management programs delivered by physiotherapists that consist of education, weight loss information for osteoarthritis and exercise.

[1] Messier SP, Mihalko SL, Legault C, et al. Effects of Intensive Diet and Exercise on Knee Joint Loads, Inflammation, and Clinical Outcomes Among Overweight and Obese Adults With Knee Osteoarthritis: The IDEA Randomized Clinical Trial. JAMA. 2013

[2] Messier SP, Beavers DP, Mihalko SL, et al. The effects of intensive dietary weight loss and exercise on gait in overweight and obese adults with knee osteoarthritis. The Intensive Diet and Exercise for Arthritis (IDEA) trial. J Biomechanics. 2020.