Overweight and obese patients with the joint disorder who followed an 18-month diet and exercise plan lost more than 10% of body weight and experienced less pain than those undertaking exercise alone.
Patients also saw bigger falls in inflammation levels, better function of their knee joints and greater improvements in health-related quality of life, the US study found.
In the 18-month study, Stephen Messier PhD of Wake Forest University in North Carolina and colleagues randomised 454 knee osteoarthritis patients with a BMI of ≥27 to either an intensive diet-induced weight loss programme, an exercise programme, or a combination of the two.
The dietary weight-loss plan saw patients drink meal-replacement shakes for two meals a day and limit calorie intake for the third. For the exercise plan, patients took part in walking and strength training at one-hour sessions, three times a week.
After 18 months, 399 patients completed the study. Those on the diet-only plan on average lost 8.9kg (9.5% of body weight) compared with 10.6kg (11.4%) among those on the combination plan. In contrast, patients on the exercise-only plan lost just 1.8kg (2%).
Peak knee compressive force, a measure of joint loading, was lower after 18 months in the diet group than the exercise group. Levels of plasma interleukin-6, a marker of inflammation, dropped further in the combination and diet-only groups than the exercise-only group.
Similarly, patients on the weight loss and exercise plan registered lower pain scores and better knee function, and walked further and faster in a six-minute walk test than those on the exercise-only programme. Physical health-related quality of life also showed greater improvements.
The researchers concluded: 'The findings suggest intensive weight loss may have anti-inflammatory and biomechanical benefits; when combining weight loss with exercise, patients can safely achieve a mean long-term weight loss of more than 10%, with an associated improvement in symptoms greater than with either intervention alone.'