Effect of diet-induced weight loss on osteoarthritic knee pain

Clinical question

Will diet-induced weight loss (DWL) reduce osteoarthritic (OA) knee pain in overweight and obese adults?

Bottom line

Observational data suggest that obesity may be a risk factor in developing OA. Trials reporting DWL alone (eg, 8% weight loss) show limited, likely clinically insignificant improvements in OA pain (about 5 points on 100-point pain scale) compared with control.

Evidence

• In the highest-quality systematic review and meta-analysis¹ (4 RCTs, 676 patients, mean body mass index [BMI] = 35), mean weight loss was 8% (8.5 kg) for the DWL group versus 3% (2.7 kg) for the control group. There was statistical improvement in pain scores with the DWL cohort. The effect size = 0.33, which is equal to improving about 5 points on a 100-point pain scale.² Pain scores improved 2 to 9 points on a 100-point scale. However, a change of 9 to 10 points is needed to be clinically detectable.³

• In another systematic review and meta-analysis of DWL versus control, mean BMI = 34.⁴ The changes in pain scores from the DWL group were not statistically different from the control group (5 RCTs, 616 patients). However, DWL plus exercise resulted in statistical improvement in pain scores versus control (3 RCTs, 264 patients, effect size = 0.37). Pain scores improved by 2 to 11 points on a 100-point pain scale.

• Limitations: Relevant studies were excluded.

Context

• A meta-analysis of 22 cohort studies found that patients with a BMI greater than 30 were twice as likely to have knee OA (odds ratio = 2.66).⁵

• An RCT (mean BMI = 35) reported that intensive diet and exercise interventions prevented development of knee pain at 1 year (secondary analysis).⁶ Guidelines recommend education and exercise programs with or without dietary weight management for knee OA, citing insufficient evidence for dietary management alone.⁷ In a meta-analysis of OA patients, 47% who received exercise therapy achieved a meaningful reduction in pain versus 21% in the control group.⁸

• No RCTs examined more substantial forms of weight loss (ie, bariatric surgery) and knee pain management. Observational data suggest surgically induced weight loss of 15% to 35% resulted in 75% of people experiencing some knee pain improvement.⁹

• If weight loss is desired, patients should choose a diet that they can adhere to and that works for them.¹⁰

Implementation

Dietary weight loss is beneficial in treating other conditions, such as diabetes (remission occurs in 57% of patients who lose 10 to 15 kg, and up to 86% of patients who lose > 15 kg)¹¹ and hypertension (blood pressure is reduced, but mortality and morbidity outcomes are unclear).¹² For clinically significant reductions in OA pain, exercise, intra-articular corticosteroids, and topical nonsteroidal anti-inflammatory drugs are non-surgical interventions.⁸ Clinicians should emphasize primary prevention of obesity. Any weight-loss regimens should contain regular low-impact exercise.