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

Messier SP, Mihalko SL, Legault C, et al. · JAMA

Diet plus exercise produced a 10.6 kg mean loss and less pain than either exercise alone (WOMAC 3.6 vs 4.7, p = .004) or diet alone (p = .001), with better function against both and a faster walk. On the trial's two actual primary endpoints the picture is narrower: IL-6 was lower in both diet arms than in exercise alone, but knee compressive force separated only for diet against exercise (200 N, p = .007) — the diet-plus-exercise comparison against exercise was not significant. Diet alone matched diet plus exercise on joint load and inflammation and got half the pain reduction, which the authors say they cannot explain.

Population

Overweight/obese adults >=55 with radiographic symptomatic knee OA, 18 months

Intervention

Intensive diet-induced weight loss (target >=10%) alone, or with exercise

Comparator

Exercise alone, and diet alone — three arms compared pairwise

Limitations

Single-blind (participants knew their group); older overweight population; no cartilage-structure endpoint — the primary endpoints were interleukin-6 and knee compressive force, with pain and function prespecified and powered as secondaries. The authors say the clinical significance of a 1.02-point difference on a 20-point WOMAC pain scale is uncertain, and baseline pain averaged 6.5 of 20, leaving little room to improve. Exercise adherence fell to 54-58% by 18 months. The interleukin-6 difference between diet-plus-exercise and exercise is reported at p = 0.007 with a confidence interval that crosses zero. Funded by the National Institutes of Health and by General Nutrition Centers, a supplement retailer.