Saturated fat, the estimated absolute risk and certainty of risk for mortality and major cancer and cardiometabolic outcomes: an overview of systematic reviews

Jhalok Ronjan Talukdar; Jeremy P Steen; Joshua Z Goldenberg; Qian Zhang; Robin W M Vernooij; Long Ge; Dena Zeraatkar; Małgorzata M Bała; Geoff D C Ball; Lehana Thabane; Bradley C Johnston

doi:10.1186/s13643-023-02312-3

Saturated fat, the estimated absolute risk and certainty of risk for mortality and major cancer and cardiometabolic outcomes: an overview of systematic reviews

Syst Rev. 2023 Sep 30;12(1):179. doi: 10.1186/s13643-023-02312-3.

Authors

Jhalok Ronjan Talukdar¹, Jeremy P Steen², Joshua Z Goldenberg^{3

4}, Qian Zhang⁵, Robin W M Vernooij^{6

7}, Long Ge^{1

8}, Dena Zeraatkar^{1

9}, Małgorzata M Bała¹⁰, Geoff D C Ball¹¹, Lehana Thabane^{1

12

13}, Bradley C Johnston^{14

15}

Affiliations

¹ Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, ON, Canada.
² Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada.
³ Department of Nutrition, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX, USA.
⁴ Helfgott Research Institute, National University of Natural Medicine, Portland, OR, USA.
⁵ School of Nursing, Faculty of Health Sciences, University of Ottawa, Ottawa, ON, Canada.
⁶ Department of Nephrology and Hypertension, University Medical Center Utrecht, Utrecht, The Netherlands.
⁷ Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands.
⁸ Evidence Based Social Science Research Centre, School of Public Health, Lanzhou University, Lanzhou, China.
⁹ Department of Biomedical Informatics, Harvard Medical School, Boston, MA, USA.
¹⁰ Department of Hygiene and Dietetics, Chair of Epidemiology and Preventive Medicine, Jagiellonian University Medical College, Krakow, Poland.
¹¹ Department of Pediatrics, Faculty of Medicine & Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada.
¹² Faculty of Health Sciences, University of Johannesburg, Johannesburg, South Africa.
¹³ Biostatistics Unit, St Joseph's Healthcare-Hamilton, Hamilton, ON, Canada.
¹⁴ Department of Nutrition, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX, USA. bradley.johnston@tamu.edu.
¹⁵ Department of Epidemiology and Biostatistics, School of Public Health, Texas A&M University, College Station, TX, USA. bradley.johnston@tamu.edu.

Abstract

Objective: To assess the impact of reducing saturated fat or fatty foods, or replacing saturated fat with unsaturated fat, carbohydrate or protein, on the risk of mortality and major cancer and cardiometabolic outcomes in adults.

Methods: We searched MEDLINE, EMBASE, CINAHL, and references of included studies for systematic reviews and meta-analyses (SRMAs) of randomized controlled trials (RCTs) and observational studies in adults published in the past 10 years. Eligible reviews investigated reducing saturated fat or fatty foods or replacing saturated fat with unsaturated fat, carbohydrate or protein, on the risk of cancer and cardiometabolic outcomes and assessed the certainty of evidence for each outcome using, for example, the GRADE (Grading of Recommendations, Assessment, Development, and Evaluations) approach. We assessed the quality of SRMAs using a modified version of AMSTAR-2. Results were summarized as absolute estimates of effect together with the certainty of effects using a narrative synthesis approach.

Results: We included 17 SRMAs (13 reviews of observational studies with follow-up 1 to 34 years; 4 reviews of RCTs with follow-up 1 to 17 years). The quality of two-thirds of the SRMAs was critically low to moderate; the main limitations included deficient reporting of study selection, absolute effect estimates, sources of funding, and a priori subgroups to explore heterogeneity. Our included reviews reported > 100 estimates of effect across 11 critically important cancer and cardiometabolic outcomes. High quality SRMAs consistently and predominantly reported low to very low certainty evidence that reducing or replacing saturated fat was associated with a very small risk reduction in cancer and cardiometabolic endpoints. The risk reductions where approximately divided, some being statistically significant and some being not statistically significant. However, based on 2 moderate to high quality reviews, we found moderate certainty evidence for a small but important effect that was statistically significant for two outcomes (total mortality events [20 fewer events per 1000 followed] and combined cardiovascular events [16 fewer per 1000 followed]). Conversely, 4 moderate to high quality reviews showed very small effects on total mortality, with 3 of these reviews showing non-statistically significant mortality effects.

Conclusion: Systematic reviews investigating the impact of SFA on mortality and major cancer and cardiometabolic outcomes almost universally suggest very small absolute changes in risk, and the data is based primarily on low and very low certainty evidence.

Systematic review registration: PROSPERO CRD42020172141.

Keywords: Cancer; Cardiovascular disease; Nutrition; Saturated fatty acids; Systematic review.

Publication types

Review
Research Support, Non-U.S. Gov't

MeSH terms

Adult
Carbohydrates
Cardiovascular Diseases*
Fats, Unsaturated
Humans
Neoplasms*
Systematic Reviews as Topic

Substances

Carbohydrates
Fats, Unsaturated