Reduction in saturated fat intake for cardiovascular disease
Lee Hooper, Nicole Martin, Oluseyi F Jimoh, Christian Kirk, Eve Foster, Asmaa S Abdelhamid - Cochrane Database of Systematic Reviews, 2020
This Cochrane meta-analysis of long-term randomised trials found that reducing saturated fat intake for at least two years cut combined cardiovascular events by about 17% (RR 0.83). Critically, it had little or no effect on all-cause mortality (RR 0.96) or cardiovascular mortality (RR 0.95). Benefit was greatest when saturated fat was replaced with polyunsaturated fat or carbohydrate, and was accompanied by only small reductions in cholesterol, weight, and BMI.
Key findings
- Reducing saturated fat lowered combined cardiovascular events by 17% (RR 0.83; 95% CI 0.70-0.98; 12 trials, 53,758 participants; GRADE moderate-quality).
- Little or no effect on all-cause mortality (RR 0.96; 95% CI 0.90-1.03; 11 trials, 55,858 participants) - a null result.
- Little or no effect on cardiovascular mortality (RR 0.95; 95% CI 0.80-1.12; 10 trials, 53,421 participants) - a null result.
- Benefit appeared greatest when saturated fat was replaced with polyunsaturated fat or carbohydrate, alongside only small reductions in total and LDL cholesterol, weight, and BMI.
Effect measures
- Other: RR 0.83 (risk ratio)95% CI 0.70-0.98
- Relative Risk Reduction: 17%derived from RR 0.83 (0.70-0.98)
- Other: RR 0.96 (risk ratio)95% CI 0.90-1.03
- Other: RR 0.95 (risk ratio)95% CI 0.80-1.12
Why this evidence tier (High)
- Risk of bias:
- Pools randomised controlled trials of at least 24 months, the strongest design for a causal dietary question; Cochrane methodology with systematic risk-of-bias assessment.
- Precision:
- Roughly 59,000 participants; the combined cardiovascular events interval excludes the null, while the mortality intervals are tight enough to call those effects little or none.
- Directness:
- Directly tests the intervention of interest - reducing or modifying dietary saturated fat - on clinical events and mortality.
- Consistency:
- Moderate heterogeneity for the events outcome (I-squared = 67%); benefit concentrated where saturated fat was replaced by polyunsaturated fat or carbohydrate.
- Funding / COI:
- Funded by the World Health Organization, a public-health (non-industry) funder. Lead author Lee Hooper received WHO travel funding and her institution received WHO grant support; co-author Oluseyi Jimoh was supported by WHO grant funding. The other authors declared no conflicts. No commercial conflict that would bias toward the null mortality finding.
High certainty that reducing saturated fat reduces cardiovascular events, with little or no effect on total or cardiovascular mortality - the strongest RCT-level evidence on the question.
- Population:
- Adults with and without existing cardiovascular disease from RCTs of at least 24 months; the combined-events analysis pooled 12 trials and 53,758 participants randomised to reduced or modified dietary saturated fat versus usual diet.
- Conflicts of interest:
- Funded by the World Health Organization. Lee Hooper received WHO travel funding and institutional grant support; Oluseyi Jimoh was supported by WHO grant funding; the remaining authors declared no conflicts. A public-health funder, not industry.
- Funding:
- World Health Organization (WHO) grant; review update partly WHO-funded.
Limitations
- Cites the current pub3 version (August 2020); the earlier pub2 reported a slightly larger combined-events effect (21%, RR 0.79), revised down to 17% (RR 0.83) in pub3.
- Moderate statistical heterogeneity (I-squared = 67%) across the combined-events trials.
- Cholesterol, weight, and BMI reductions achieved by the interventions were small, limiting the size of any expected clinical benefit.
- No demonstrated effect on all-cause or cardiovascular mortality despite the reduction in combined events.