A Cochrane review [Abstract] 1 included 44 trials, with a total of 18 175 subjects/clusters, with 52 intervention arms comparing dietary advice with no advice. Dietary advice reduced total serum cholesterol by 0.15 mmol/L (95% CI 0.06 to 0.23) and LDL cholesterol by 0.16 mmol/L (95% CI 0.08 to 0.24) after 3-24 months. Mean HDL cholesterol levels and triglyceride levels were unchanged. Dietary advice reduced blood pressure by 2.61 mmHg systolic (95% CI 1.31 to 3.91) and 1.45 mmHg diastolic (95% CI 0.68 to 2.22) and 24-hour urinary sodium excretion by 40.9 mmol (95% CI 25.3 to 56.5) after 3-36 months but there was heterogeneity between trials for the latter outcome. Three trials reported plasma antioxidants, where small increases were seen in lutein and β-cryptoxanthin, but there was heterogeneity in the trial effects.
Compared to no advice, dietary advice increased self-reported fruit and vegetable intake by by 1.18 servings/day (95% CI 0.65 to 1.71). Dietary fibre intake increased with advice by 6.5 g/day (95% CI 2.2 to 10.82), while total dietary fat as a percentage of total energy intake fell by 4.48 % (95% CI 2.47 to 6.48) with dietary advice and saturated fat intake fell by 2.39 % (95% CI 1.4 to 3.37). Self-reported dietary intake may be subject to reporting bias, and there was significant heterogeneity in all these analyses.
Two trials analysed incident cardiovascular disease (CVD) events (TOHP I/II). Follow-up was 77% complete at 10 to 15 years after the end of the intervention period and estimates of event rates lacked precision but suggested that sodium restriction advice probably led to a reduction in cardiovascular events (combined fatal plus non-fatal events) plus revascularisation (TOHP I hazards ratio (HR) 0.59, 95% CI 0.33 to 1.08; TOHP II HR 0.81, 95% CI 0.59 to 1.12).
Comment: The quality of evidence is downgraded by study limitations (methods used in randomisation, allocation concealment and blinding).
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