Evidence from five RCTs of weight loss in people with osteoarthritis of the knee suggests that function can be improved, provided the weight loss is sufficient. Results on the effect on pain were inconsistent, and difficult to distinguish from possible effects of exercise, as, in the most informative RCT, exercise was part of a complex intervention to lose weight. There is no evidence that weight loss (with or without exercise) can slow the progression of osteoarthritis. There is no evidence on the effects of weight loss on osteoarthritis of the hip, hand, or other joints.

The National Institute for Health and Clinical Excellence (NICE) conducted a systematic review of the effects of weight loss on osteoarthritis [National Collaborating Centre for Chronic Conditions, 2008]. Evidence was summarized from one systematic review, and meta-analysis of four RCTs and one additional RCT. All five RCTs studied people with osteoarthritis of the knee. NICE found no trials assessing the effect of weight loss on osteoarthritis of other joints.

• Pain:
• The meta-analysis found that weight loss had no significant effect on pain.
• Function/disability:
• The meta-analysis found significant effects on self-reported disability but not on global disability.
• Quality of life:
• One RCT (n = 316) compared the effects of four interventions on the quality of life reported by people with osteoarthritis of the knee: dietary weight loss alone, exercise alone, dietary weight loss plus exercise, or healthy lifestyle control.
• Compared with the healthy lifestyle control group, the dietary weight loss group were significantly more satisfied with their functioning. However, on nine other measures of quality of life, the differences were not significant.
• The other between-group comparisons had similar mixed results.