Randomised controlled trials (RCTs) and quasi-experimental studies of weight loss via energy restriction alone, exercise alone or exercise plus energy restriction in middle-aged or older adults were eligible for inclusion. Study participants had to have a mean age greater than 50 years, mean body mass index (BMI) greater than 25kg/m2 and not be a smoker or diabetic; female participants had to be postmenopausal. Studies had to report on changes in fat-free mass using a valid method: dual energy x-ray absorptiometry, air displacement plethysmography, total body potassium or hydrostatic weighing. Studies where skin folds or bioelectrical impedance were used to measure fat-free mass were excluded. Studies in participants with osteoarthritis and mean BMI less than 25kg/m2 and studies with a duration of less than six weeks or that had very low calorie diets (≤800 calories per day) were excluded.
The included studies considered various programmes of energy restriction only, exercise only, energy restriction combined with exercise and multiple intervention groups of exercise and energy restriction. The duration of intervention varied from nine to 52 weeks. Exercise interventions were primarily aerobic; resistance training was also included. The energy restriction interventions varied: some provided a proportion of all food and drink; others used diet counselling and did not provide food and drink.
The authors did not state how many reviewers were involved in study selection.