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Evidence summaries

Effect of Dietary Interventions on Diet and Cardiovascular Risk Factors

Dietary advice from health personnel appears to be effective in reducing blood lipid levels, blood pressure and dietary fat intake, and increasing fruit and vegetable intake. Level of evidence: "B"

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).

References

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