Reduction in saturated fat intake for cardiovascular disease.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 32428300 · doi:10.1002/14651858.CD011737.pub2
What was done
Authors conducted a Cochrane systematic review and meta-analysis (searches updated to October 2019 across CENTRAL, MEDLINE, Embase, Clinicaltrials.gov, and ICTRP) of randomized controlled trials in adults with or without CVD comparing reduced saturated fat intake (or altered dietary fats achieving saturated fat reduction) to usual diet or higher saturated fat intake. Trials were required to have an intervention duration of at least 24 months and report mortality or cardiovascular morbidity. Random-effects meta-analyses, meta-regressions, subgroup analyses, and GRADE certainty assessments were performed.
What was found
Across 15 RCTs (16 comparisons, ~59,000 participants), reducing dietary saturated fat reduced combined cardiovascular events by 21% (RR 0.79, 95% CI 0.66 to 0.93; 11 trials, 53,300 participants; I² = 65%; GRADE moderate quality). The number needed to treat for an additional beneficial outcome (NNTB) was 56 in primary prevention trials and 32 in secondary prevention trials over ~4 years. Meta-regression indicated greater saturated fat reductions (and larger serum cholesterol drops) yielded larger CVD event reductions. There was little or no effect on all-cause mortality (RR 0.96, 95% CI 0.90 to 1.03; 11 trials, 55,858 participants; GRADE moderate quality), cardiovascular mortality (RR 0.95, 95% CI 0.80 to 1.12; 10 trials, 53,421 participants; GRADE moderate quality), non-fatal MI (RR 0.97, 95% CI 0.87 to 1.07; low quality), or CHD mortality (RR 0.97, 95% CI 0.82 to 1.16; low quality). Effects on total MI, stroke, and CHD events were unclear due to very low-quality evidence. Saturated fat reduction produced small decreases in weight, BMI, total cholesterol, and LDL cholesterol, with no effect on HDL cholesterol, triglycerides, blood pressure, diabetes diagnosis, cancer incidence, or cancer mortality.
Why it matters
This review establishes that reducing saturated fat intake for at least two years provides a clinically meaningful reduction in combined cardiovascular events, though it does not significantly reduce total or cardiovascular mortality over trial follow-up periods.
Limits
Substantial heterogeneity was present for combined cardiovascular events (I² = 65%). Evidence certainty for specific ischemic outcomes including stroke, total MI, and CHD events was low to very low. Data evaluating replacement of saturated fat specifically with monounsaturated fats or protein were very limited, and trial interventions varied considerably from dietary advice to full provision of food.