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Meta-Analysis
. 2015 Aug 11:351:h3978.
doi: 10.1136/bmj.h3978.

Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies

Russell J de Souza  1 , Andrew Mente  2 , Adriana Maroleanu  3 , Adrian I Cozma  4 , Vanessa Ha  5 , Teruko Kishibe  6 , Elizabeth Uleryk  7 , Patrick Budylowski  8 , Holger Schünemann  9 , Joseph Beyene  10 , Sonia S Anand  11
Affiliations
Meta-Analysis

Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies

Russell J de Souza et al. BMJ. .

Abstract

Objective: To systematically review associations between intake of saturated fat and trans unsaturated fat and all cause mortality, cardiovascular disease (CVD) and associated mortality, coronary heart disease (CHD) and associated mortality, ischemic stroke, and type 2 diabetes.

Design: Systematic review and meta-analysis.

Data sources: Medline, Embase, Cochrane Central Registry of Controlled Trials, Evidence-Based Medicine Reviews, and CINAHL from inception to 1 May 2015, supplemented by bibliographies of retrieved articles and previous reviews.

Eligibility criteria for selecting studies: Observational studies reporting associations of saturated fat and/or trans unsaturated fat (total, industrially manufactured, or from ruminant animals) with all cause mortality, CHD/CVD mortality, total CHD, ischemic stroke, or type 2 diabetes.

Data extraction and synthesis: Two reviewers independently extracted data and assessed study risks of bias. Multivariable relative risks were pooled. Heterogeneity was assessed and quantified. Potential publication bias was assessed and subgroup analyses were undertaken. The GRADE approach was used to evaluate quality of evidence and certainty of conclusions.

Results: For saturated fat, three to 12 prospective cohort studies for each association were pooled (five to 17 comparisons with 90,501-339,090 participants). Saturated fat intake was not associated with all cause mortality (relative risk 0.99, 95% confidence interval 0.91 to 1.09), CVD mortality (0.97, 0.84 to 1.12), total CHD (1.06, 0.95 to 1.17), ischemic stroke (1.02, 0.90 to 1.15), or type 2 diabetes (0.95, 0.88 to 1.03). There was no convincing lack of association between saturated fat and CHD mortality (1.15, 0.97 to 1.36; P=0.10). For trans fats, one to six prospective cohort studies for each association were pooled (two to seven comparisons with 12,942-230,135 participants). Total trans fat intake was associated with all cause mortality (1.34, 1.16 to 1.56), CHD mortality (1.28, 1.09 to 1.50), and total CHD (1.21, 1.10 to 1.33) but not ischemic stroke (1.07, 0.88 to 1.28) or type 2 diabetes (1.10, 0.95 to 1.27). Industrial, but not ruminant, trans fats were associated with CHD mortality (1.18 (1.04 to 1.33) v 1.01 (0.71 to 1.43)) and CHD (1.42 (1.05 to 1.92) v 0.93 (0.73 to 1.18)). Ruminant trans-palmitoleic acid was inversely associated with type 2 diabetes (0.58, 0.46 to 0.74). The certainty of associations between saturated fat and all outcomes was "very low." The certainty of associations of trans fat with CHD outcomes was "moderate" and "very low" to "low" for other associations.

Conclusions: Saturated fats are not associated with all cause mortality, CVD, CHD, ischemic stroke, or type 2 diabetes, but the evidence is heterogeneous with methodological limitations. Trans fats are associated with all cause mortality, total CHD, and CHD mortality, probably because of higher levels of intake of industrial trans fats than ruminant trans fats. Dietary guidelines must carefully consider the health effects of recommendations for alternative macronutrients to replace trans fats and saturated fats.

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Conflict of interest statement

Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: RJdeS has received a Canadian Institutes for Health Research (CIHR) postdoctoral fellowship. VH has received a Province of Ontario graduate scholarship and research support from the Canadian Institutes of Health Research (CIHR). AIC has received a Province of Ontario graduate scholarship.

Figures

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Fig 1 PRISMA summary of evidence search and selection for saturated fat and health outcomes (up to 1 May 2015)
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Fig 2 Summary most adjusted relative risks for saturated fat intake and all cause mortality, CHD mortality, CVD mortality, total CHD, ischemic stroke, and type 2 diabetes. All effect estimates are from random effects analyses. P value is for Z test of no overall association between exposure and outcome; Phet is for test of no differences in association measure among studies; I2 is proportion of total variation in study estimates from heterogeneity rather than sampling error
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Fig 3 PRISMA summary of evidence search and selection for trans unsaturated fat and health outcomes (up to 1 May 2015)
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Fig 4 Summary most adjusted relative risks of total trans fat, industrial trans fat, and ruminant trans fat and all cause mortality, CHD mortality, total CHD, ischemic stroke, and type 2 diabetes. For total trans fats effect estimate for is fixed effect analysis; all others random effects analyses. P value is for Z test of no overall association between exposure and outcome; Phet is for test of no differences in association measure among studies; I2 is proportion of total variation in study estimates from heterogeneity rather than sampling error
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Comment in

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