Dietary advice for reducing cardiovascular risk

Diet is an important determinant of chronic disease risk, particularly heart disease. This review assessed the effects of providing dietary advice to healthy adults in order to produce sustained improvements in their diets. Whether dietary improvement would reduce the risk factors associated with heart disease was also examined. We found 44 trials in which healthy adults were randomly assigned to receive dietary advice or no dietary advice. The dietary improvements recommended to the people in the intervention groups centred largely on the reduction of salt and fat intake and an increase in the intake of fruit, vegetables and fibre. Advice was delivered in a variety of ways, including one-to-one contact, group sessions and written materials. There were variations in intensity of the intervention, ranging from one contact per study participant to 50 hours of counselling over four years. The duration of the trials ranged from three months to four years, with a median follow-up period of 12 months. There was some evidence of greater effectiveness in people told that they were at risk of heart disease or cancer. Modest improvements were shown in cardiovascular risk factors, such as blood pressure and total and LDL-cholesterol levels. In the trials that separated effects by gender, women tended to make larger reductions in fat intake but there was insufficient evidence to show whether this translated to a larger reduction in total cholesterol levels. Two trials followed people up 10 to 15 years after the end of the trials and showed that the beneficial changes in cardiovascular risk factors may have resulted in a reduced incidence of heart disease, stroke or heart attack, although more evidence is needed to confirm this.

Authors' conclusions: 

Dietary advice appears to be effective in bringing about modest beneficial changes in diet and cardiovascular risk factors over approximately 12 months, but longer-term effects are not known.

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Background: 

Changes in population diet are likely to reduce cardiovascular disease and cancer, but the effect of dietary advice is uncertain. This review is an update of a previous review published in 2007.

Objectives: 

To assess the effects of providing dietary advice to achieve sustained dietary changes or improved cardiovascular risk profile among healthy adults.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials, the Database of Abstracts of Reviews of Effects (DARE) and the HTA database on The Cochrane Library (Issue 4, 2010). We searched MEDLINE (Ovid) (1950 to week 2 October 2010) and EMBASE (Ovid) (1980 to Week 42 2010). Additional searches were done on CAB Health (1972 to December 1999), CVRCT registry (2000), CCT (2000) and SIGLE (1980 to 2000). Dissertation abstracts and reference lists of articles were checked and researchers were contacted.

Selection criteria: 

Randomised studies with no more than 20% loss to follow-up, lasting at least three months and involving healthy adults comparing dietary advice with no advice or minimal advice. Trials involving children, trials to reduce weight or those involving supplementation were excluded.

Data collection and analysis: 

Two review authors independently assessed trial quality and extracted data. Study authors were contacted for additional information.

Main results: 

Forty-four trials with 52 intervention arms (comparisons) comparing dietary advice with no advice were included in the review; 18,175 participants or clusters were randomised. Twenty-nine of the 44 included trials were conducted in the USA. 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 to 24 months. Mean HDL cholesterol levels and triglyceride levels were unchanged. Dietary advice reduced blood pressure by 2.61 mm Hg systolic (95% CI 1.31 to 3.91) and 1.45 mm Hg 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 to 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. Self-reported dietary intake may be subject to reporting bias, and there was significant heterogeneity in all the following analyses. Compared to no advice, dietary advice increased fruit and vegetable intake 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).

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).

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