RecruitingBehavioural interventionThe Osteoarthritis Prevention StudyThe goal of this study is to establish the efficacy of an intervention of dietary weight loss, exercise, and weight-loss maintenance for knee Osteoarthritis (OA) prevention in adult females aged ≥ 50 years with obesity and no or infrequent knee pain. The primary aim is to compare the effects of a dietary weight loss, exercise, and weight-loss maintenance to an attention control group in preventing the development of structural Magnetic Resonance Imaging (MRI) knee OA. Secondary aims will determine the intervention effects on pain, mobility, health-related quality of life, knee joint compressive forces, inflammatory measures, weight loss, exercise self-efficacy, and cost-effectiveness of this intervention.