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.
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.


METHODS
Systematic review and meta-analysis.


METHODS
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.


METHODS
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.


METHODS
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.
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada Chanchlani Research Centre, McMaster University, Hamilton, ON, Canada Department of Nutritional Sciences, University of Toronto, Toronto, ON, Canada Clinical Nutrition and Risk Factor Modification Center, St Michael's Hospital, Toronto, ON, Canada.
Russell J
RJ
de Souza
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada Chanchlani Research Centre, McMaster University, Hamilton, ON, Canada Population Health Research Institute, Hamilton Health Sciences, Hamilton, ON, Canada.
Andrew
A
Mente
Chanchlani Research Centre, McMaster University, Hamilton, ON, Canada.
Adriana
A
Maroleanu
Department of Nutritional Sciences, University of Toronto, Toronto, ON, Canada Clinical Nutrition and Risk Factor Modification Center, St Michael's Hospital, Toronto, ON, Canada.
Adrian I
AI
Cozma
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada Department of Nutritional Sciences, University of Toronto, Toronto, ON, Canada Clinical Nutrition and Risk Factor Modification Center, St Michael's Hospital, Toronto, ON, Canada anands@mcmaster.ca.
Vanessa
V
Ha
Scotiabank Health Sciences Library, St Michael's Hospital, Toronto, ON, Canada.
Teruko
T
Kishibe
Hospital Library and Archives, Hospital for Sick Children, Toronto, ON, Canada.
Elizabeth
E
Uleryk
Clinical Nutrition and Risk Factor Modification Center, St Michael's Hospital, Toronto, ON, Canada.
Patrick
P
Budylowski
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada Department of Medicine, McMaster University, Hamilton, ON, Canada.
Holger
H
Schünemann
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada Chanchlani Research Centre, McMaster University, Hamilton, ON, Canada.
Joseph
J
Beyene
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada Chanchlani Research Centre, McMaster University, Hamilton, ON, Canada Population Health Research Institute, Hamilton Health Sciences, Hamilton, ON, Canada Department of Medicine, McMaster University, Hamilton, ON, Canada anands@mcmaster.ca.
Sonia S
SS
Anand
D003327:Coronary Disease / Q000401:mortality; D003924:Diabetes Mellitus, Type 2 / Q000401:mortality*; D003925:Diabetic Angiopathies / Q000401:mortality*; D004812:Epidemiologic Methods; D005227:Fatty Acids / Q000009:adverse effects*; D006801:Humans; D020521:Stroke / Q000401:mortality*; D044242:Trans Fatty Acids / Q000009:adverse effects*
D005227:Fatty Acids; D044242:Trans Fatty Acids