Randomised controlled trials (RCTs), including cluster-RCTs, that evaluated the promotion of a healthy dietary pattern or its constituent food groups (increased fruit and vegetables; legumes or pulses; nuts and seeds; unrefined cereals; olive oil; fish; moderate consumption of wine; low consumption of meat and meat products) in adults with a mean/median age of between 54 to 70 years were eligible for inclusion. Only studies conducted in developed countries were included. Studies that involved non-institutionalised adults with or without health risk factors were included. Studies that investigated lifestyle interventions such as physical activity were included so long as effects of the diet component were reported independently. Only interventions with a follow-up of more than three months were eligible. Studies that promoted other dietary patterns, laboratory feeding trials, studies on change in a specific macro/micro nutrient, studies that promoted prefabricated diet foods or meal replacement drinks and studies that tested dietary supplements were excluded. The primary outcome of interest was dietary behaviour change (defined in the review).
Studies were conducted in Europe and North America. Mean ages ranged from 54 to 67 years. Most participants were overweight and obese. Most studies used food frequency questionnaires (FFQ) or fruit and vegetables screener questionnaires to assess self-reported food intake. Interventions included promoting a Mediterranean diet, plant-based diet, dietary pattern intended to decrease fat intake and consumption of fruit and vegetables. Treatment delivery, intensity and setting and people who provided the treatments varied between studies.
Two reviewers independently selected studies for inclusion. Discrepancies between reviewers were resolved through discussion with a third reviewer.