Sixty-six RCTs were included. Thirteen trials were classed as good quality and the others were fair. Most trials did not report intervention fidelity or adherence. Seven studies were included that addressed harm. Only 11 trials provided follow-up of longer than 12 months.
Health outcomes (three RCTs): There was evidence from observational follow-up of a trial population with mildly elevated diastolic blood pressure (n=3,126) of fewer cardiovascular events and revascularisation following intensive sodium restriction counselling compared to control (HR 0.70 95% CI 0.53 to 0.94), but no difference in mortality after 10 to 15 years follow-up. A trial of postmenopausal women ( n=48,835) found no evidence of a reduction in major coronary heart disease events at 8.1 years follow-up after an intensive low-fat diet counselling intervention.
Intermediate outcomes: High intensity dietary counselling interventions (with or without physical activity) were associated with reductions in body mass index that ranged from 0.3 to 0.7kg/m2 (high heterogeneity with pooled effect), systolic blood pressure (MD -1.5mm/Hg 95%, CI -2.1 to -0.9; 10 RCTs), diastolic blood pressure (MD -0.7mm/Hg, 95% CI -0.9 to -0.6; 10 RCTs), total cholesterol (MD -0.17 mmol/L, 95% CI -0.25 to -0.09; six RCTs) and low-density lipoprotein cholesterol (MD -0.13mmol/L, 95% CI -0.21 to -0.06; six RCTs). Heterogeneity ranged from low to moderate. There was limited evidence of benefit moderate intensity dietary interventions with or without physical activity and none for low intensity. Physical activity interventions were of medium or low intensity and there was limited evidence of benefit from the pooled analyses.
Behavioural outcomes: Medium and high intensity interventions were associated with improvements in self-reported physical activity and dietary behaviours. For some outcomes low intensity interventions were associated with a benefit. Heterogeneity was high for many of the pooled effects.
Harms: Adverse effects related to interventions that targeted physical activity were rare. Based on seven observational studies there was a two- to 17-fold increased risk of a cardiac event during vigorous exertion. None of the studies of dietary counselling addressed assessed adverse effects.
There was no strong evidence of publication bias.