BMJ 2001;322:757-763 ( 31 March )

Papers
Dietary fat intake and prevention of cardiovascular disease: systematic review
Lee Hooper, research associate in evidence based care and systematic review a, Carolyn D Summerbell, reader in human nutrition b, Julian P T Higgins, statistician c, Rachel L Thompson, senior research fellow in public health nutrition d, Nigel E Capps, consultant chemical pathologist for Shropshire e, George Davey Smith, professor of clinical epidemiology f, Rudolph A Riemersma, senior lecturer in cardiac biochemistry g, Shah Ebrahim, professor in epidemiology of ageing f.

a Manchester Dental and Education Centre (MANDEC), University Dental Hospital of Manchester, Manchester M15 6FH, b School of Health, University of Teesside, Middlesbrough, Cleveland TS1 3BA, c Systematic Reviews Training Unit, Institute of Child Health, London WC1N 1EH, d Public Health Nutrition, Institute of Human Nutrition, Level B, South Academic Block, Southampton General Hospital, Southampton SO16 6YD, e Department of Clinical Biochemistry, Princess Royal Hospital NHS Trust, Apley Castle, Telford TF6 6TF, f Department of Social Medicine, University of Bristol, Canynge Hall, Bristol BS8 2PR, g Cardiovascular Research, University of Edinburgh, Edinburgh EH8 9XF

Correspondence to: L Hooper lee.hooper~man.ac.uk


Objective: To assess the effect of reduction or modification of dietary fat intake on total and cardiovascular mortality and cardiovascular morbidity.
Design: Systematic review.
Data sources: Cochrane Library, Medline, Embase, CAB abstracts, SIGLE, CVRCT registry, and biographies were searched; trials known to experts were included.
Included studies: Randomised controlled trials stating intention to reduce or modify fat or cholesterol intake in healthy adult participants over at least six months . Inclusion decisions, validity, and data extraction were duplicated. Meta-analysis (random effects methodology), meta-regression, and funnel plots were performed.
Results: 27 studies (30 902 person years of observation) were included. Alteration of dietary fat intake had small effects on total mortality (rate ratio 0.98; 95% confidence interval 0.86 to 1.12). Cardiovascular mortality was reduced by 9% (0.91; 0.77 to 1.07) and cardiovascular events by 16% (0.84; 0.72 to 0.99), which was attenuated (0.86; 0.72 to 1.03) in a sensitivity analysis that excluded a trial using oily fish. Trials with at least two years' follow up provided stronger evidence of protection from cardiovascular events (0.76; 0.65 to 0.90).
Conclusions: There is a small but potentially important reduction in cardiovascular risk with reduction or modification of dietary fat intake, seen particularly in trials of longer duration.

What is already known on this topic
The epidemiological relation between dietary fat intake and cardiovascular disease is central in strategies aimed at risk reduction in populations and individuals

Systematic review of randomised controlled trials supports manipulation of dietary fat to control serum lipid concentrations, though evidence of effect on one risk factor does not rule out an opposite or reinforced effect on another unstudied risk factor

Randomised controlled trials of dietary fat reduction or modification have shown varying results on cardiovascular morbidity and mortality

What this study adds
Systematic review of trials of modified fat intake shows that reduction or modification of dietary fat intake results in reductions in cardiovascular events, but only in trials of at least two years' duration

There is little effect on total mortality

Despite decades of effort and many thousands of people randomised, there is still only limited and inconclusive evidence of the effects of modification of total, saturated, monounsaturated, or polyunsaturated fats on cardiovascular morbidity and mortality