Context: Apart from ruminant fat, trans-fatty acids are produced during the partial hydrogenation of vegetable oils, (eg, in the production of ultraprocessed foods). Harmful cardiovascular effects of trans-fatty acids are already proven, but the link with cancer risk has not yet been summarized.
Objective: A systematic review (following PRISMA guidelines) - including observational studies on the association of trans-fatty acid intake with any cancer risk - was conducted, with no limitations on population types.
Data sources: The electronic databases PubMed and Embase were searched to identify relevant studies.
Data extraction: This systematic review included 46 articles. Quality was assessed via the Newcastle-Ottawa scale. Meta-analyses were conducted if at least 4 articles exploring the same transfat-cancer pairings were found.
Data analysis: Nineteen cancer types have been researched in cohort and case-control studies on trans-fatty acids, with breast cancer (n = 17), prostate cancer (n = 11), and colorectal cancer (n = 9) as the most researched. The meta-analyses on total trans-fat showed a significant positive association for prostate cancer (odds ratio [OR] 1.49; 95%CI, 1.13-1.95) and colorectal cancer (OR 1.26; 95%CI, 1.08-1.46) but not for breast cancer (OR 1.12; 95%CI, 0.99-1.26), ovarian cancer (OR 1.10; 95%CI, 0.94-1.28), or non-Hodgkin lymphoma (OR 1.32; 95%CI, 0.99-1.76). Results were dependent on the fatty acid subtype, with even cancer-protective associations for some partially hydrogenated vegetable oils. Enhancing moderators in the positive transfat-cancer relation were gender (direction was cancer-site specific), European ancestry, menopause, older age, and overweight.
Conclusion: Despite heterogeneity, higher risk of prostate and colorectal cancer by high consumption of trans-fatty acids was found. Future studies need methodological improvements (eg, using long-term follow-up cancer data and intake biomarkers). Owing to the lack of studies testing trans-fatty acid subtypes in standardized ways, it is not clear which subtypes (eg, ruminant sources) are more carcinogenic.
Systematic review registration: PROSPERO registration no. CRD42018105899.
Keywords: case-control studies; cohort studies; diet; neoplasms; primary prevention; trans fatty acids.
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