The relationship between adherence to the Mediterranean diet (MD), physical activity (PA), sedentary behaviour and physical fitness levels has been analysed in several studies; however, there is mixed evidence among youth. Thus, this study aimed to meta-analyse the associations between adherence to the MD, PA, sedentary behaviour and physical fitness among children and adolescents. Three databases were systematically searched, including cross-sectional and prospective designs with a sample of healthy youth aged 3–18 years. Random effects inverse-variance model with the Hartung–Knapp–Sidik–Jonkman adjustment was used to estimate the pooled effect size (correlation coefficient (r)). Thirty-nine studies were included in the meta-analysis, yielding a total of 565 421 youth (mean age, 12·4 years). Overall, the MD had a weak-to-moderate positive relationship with PA (r 0·14; 95 % CI 0·11, 0·17), cardiorespiratory fitness (r 0·22; 95 % CI 0·13, 0·31) and muscular fitness (r 0·11; 95 % CI 0·03, 0·18), and a small-to-moderate negative relationship with sedentary behaviour (r –0·15; 95 % CI –0·20, –0·10) and speed–agility (r –0·06; 95 % CI –0·12, –0·01). There was a high level of heterogeneity in all of the models (I 2 ≥ 75 %). Overall, results did not remain significant after controlling for sex and age (children or adolescents) except for PA. Improving dietary habits towards those of the MD could be associated with higher physical fitness and PA in youth, lower sedentary behaviours and better health in general.

This study aimed to evaluate the feasibility of a peer support intervention to encourage adoption and maintenance of a Mediterranean diet (MD) in established community groups where existing social support may assist the behaviour change process. Four established community groups with members at increased Cardiovascular Disease (CVD) risk and homogenous in gender were recruited and randomised to receive either a 12-month Peer Support (PS) intervention (PSG) (n 2) or a Minimal Support intervention (educational materials only) (MSG) (n 2). The feasibility of the intervention was assessed using recruitment and retention rates, assessing the variability of outcome measures (primary outcome: adoption of an MD at 6 months (using a Mediterranean Diet Score (MDS)) and process evaluation measures including qualitative interviews. Recruitment rates for community groups (n 4/8), participants (n 31/51) and peer supporters (n 6/14) were 50 %, 61 % and 43 %, respectively. The recruitment strategy faced several challenges with recruitment and retention of participants, leading to a smaller sample than intended. At 12 months, a 65 % and 76·5 % retention rate for PSG and MSG participants was observed, respectively. A > 2-point increase in MDS was observed in both the PSG and the MSG at 6 months, maintained at 12 months. An increase in MD adherence was evident in both groups during follow-up; however, the challenges faced in recruitment and retention suggest a definitive study of the peer support intervention using current methods is not feasible and refinement based on the current feasibility study should be incorporated. Lessons learned during the implementation of this intervention will help inform future interventions in this area.