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Fat consumption and cardiovascular disease

 

The association between dietary fat and cardiovascular disease has been fundamental to health messages for decades. This meta-analysis assesses the effect of reducing dietary fat consumption on cardiovascular disease and aims to quantify the effect.

Message

Reduction of dietary fat intake reduces cardiovascular events by 24% after a period of two years.

Reference

L Hooper et al. Dietary fat intake and prevention of cardiovascular disease: systematic review. British Medical Journal 2001 322: 757-763.

Search

Randomised controlled trials were searched for in the Cochrane Library, Medline, Embase, CAB abstracts, CVRCT registry (to 1998) and SIGLE (1999). Bibliographies were reviewed, and Cochrane Review Groups and 60 experts were contacted for further trials. There were no language restrictions. For trials to be included they had to be randomised; there had to be a comparison group; their aim was to reduce or modify intake of dietary fat or cholesterol; other risk factors were either not included or could be excluded from the analysis; participants were not children, acutely ill or pregnant; the trial or the follow-up period was at least six months; and results were available on mortality or cardiovascular morbidity. Inclusion was assessed independently by two reviewers.

Twenty-seven studies were identified with a total of 1,430 deaths and 1,216 cardiovascular events. Most of the events occurred in men. Only two trials included women. The number of participants either reducing or modifying their fat intake varied from 11 to 4,516 per trial. They were either given dietary advice, given advice with a supplement or provided with a diet.

The effects of reducing dietary fat consumption were assessed in relation to total mortality, cardiovascular mortality and combined cardiovascular events (including cardiovascular deaths, non-fatal myocardial infarction, stroke, angina, heart failure, peripheral vascular disease, angioplasty and coronary artery bypass grafting). The effects of the following were also examined: (i) duration of the trial, (ii) the initial level of cardiovascular risk and dietary fat intake, (iii) the type of trial and (iv) changes in intake of total, saturated, monounsaturated and polyunsaturated fats and blood cholesterol concentration.

Results

Reduction of dietary fat intake

Reduction of dietary fat consumption had no effect on total mortality (rate ratio 0.98, 95% confidence interval 0.86 to 1.12) or cardiovascular mortality (rate ratio 0.91, 95% confidence interval 0.77 to 1.07).

There was a 16% reduction in cardiovascular events (rate ratio 0.84, 95% confidence interval 0.72 to 0.99). Sixteen trials contributed to this result.

Duration of follow-up

There was no reduction in cardiovascular events in trials with an average follow-up period of less than two years (11 trials, rate ratio 0.96, 95% confidence interval 0.75 to 1.23).

A 24% reduction in cardiovascular events was observed in trials whose average length of follow-up was more than two years (5 trials, rate ratio 0.76, 95% confidence interval 0.65 to 0.90).

Initial level of cardiovascular risk

There was no reduction in cardiovascular events among participants at a low initial cardiovascular risk (9 trials, rate ratio 0.82, 0.56 to 1.20).

A 16% reduction in cardiovascular events was observed among participants at a high initial risk (7 trials, rate ratio 0.84, 0.70 to 0.99).

Initial dietary fat consumption and type of trial

Reduction in cardiovascular events was not affected by either the initial level of dietary fat intake or the method of dietary modification (by dietary advice in 5 trials, advice with a supplement in 9 trials or diet provided in 2 trials).

Changes in fat intake and blood cholesterol concentration

Examining whether changes in saturated fat, polyunsaturated fat, monounsaturated fat or serum cholesterol were responsible for the reduction of cardiovascular events, only the association between monounsaturated fat and cardiovascular events was significant (but this result was dependent to a large extent upon one trial).

Comment

The number of non-significant associations in this paper may appear surprising, but in most of the analyses the number of contributing studies was very small. A reduction in cardiovascular events was observed in participants reducing their dietary fat intake. These participants reduced their fat to within current UK guidelines: on average, total fat was reduced to 35% of total energy intake and saturated fats were reduced to 8.5% of total energy intake. Current UK guidelines are to reduce total fat to about 35% or less of total energy intake and saturated fats to 10% of total energy intake. Although this study was unable to examine the proportion of fatty acids beneficial for health, its results fit with current guidelines which emphasise a reduction in total fat and saturated fats (which increase levels of blood cholesterol and are found in animal foods and products, dairy products and oils).