Trans Fatty Acid Isomers in Mortality and Incident Coronary Heart Disease Risk

W hile nutrition remains a cornerstone to prevent adverse health outcomes, including chronic noncommunicable conditions such as cardiovascular disease (CVD) and cancer, the quantity and quality of various whole foods and nutrients to promote optimal health are still being debated. This is of particular relevance to the effects of dietary fatty acids on CVD-related outcomes, where, for instance, a supposed unfavorable role of total dietary saturated fatty acids and a beneficial role of marine omega-3 fatty acids have been questioned. Furthermore, recent epidemiological evidence suggests that when individual fatty acids are examined, associations between specific fatty acid subtypes and coronary risk may vary importantly within each family of fatty acid group considered, indicating that individual fatty acid subtypes (and their food sources) might be more relevant in determining the subsequent disease risk than any composite fatty acid group in isolation. Amidst the uncertainty regarding the optimal intake of fatty acids for cardiovascular and overall health, the evidence regarding trans fatty acids (ie, unsaturated fats with at least 1 double bond in the trans configuration) seems generally consistent. Concordant evidence from controlled trials and observational studies demonstrates that consumption of trans fatty acids adversely affects vascular risk factors, and is strongly and independently associated with a positive risk of coronary outcomes. Various landmark prospective cohort studies have reported strong increased relative risks of CVD outcomes for higher consumption of trans fat, including the Nurses’ Health Study, the Zutphen study, the Health Professionals Follow-up Study, and the Alpha-Tocopherol, Beta-Carotene trial, with a 23% overall increased risk of coronary heart disease (CHD) for each additional 2% energy intake from total trans fat when all available epidemiological evidence was combined. Additionally, similar positive associations for trans fat intake with breast cancer, ovarian cancer, and colorectal cancer have been reported. More recently, the Reasons for Geographical and Racial Differences in Stroke cohort showed that detrimental associations of total trans fat consumption on health translated to a 24% higher risk of total mortality among participants in the highest compared to the lowest quintiles of consumption at baseline. The proposed pathways through which increased levels of trans fatty acid consumption may affect health outcomes include adverse effects on intermediate risk factors such as circulating lipids, endothelial function, and inflammation. These, coupled with evidence from the epidemiologic and intervention studies, have prompted current public health guidelines in the United States (US) and many other nations to recommend restriction of trans fatty acid consumption. The US Food and Drug Administration has recently issued a preliminary statement that partially hydrogenated vegetable oil (PHVO), the major source of trans fat in processed foods, will no longer be “generally recognized as safe”—a measure that should considerably reduce the amounts of trans fat found in processed foods in the United States. Nevertheless, self-reported dietary intake assessment may be limited in the ability to accurately reflect an individual’s consumption of nutrients, due to measurement error, recall bias, selective reporting, and incompleteness of food composition databases. More importantly, dietary assessment tools are most efficient to capture total trans fatty acid consumption, leaving possible differential effects of individual trans fatty acid subtypes and specific isomers generally unaddressed, which is also reflected in the guidelines and policies that are currently targeting reduction of total trans fats (produced principally through the process of partial hydrogenation). Objective biomarkers of fatty acids, such as circulating or adipose tissue concentrations, in this regard, may provide a more accurate and comprehensive measure of dietary exposure and offer an intriguing prospect to The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association. From the Department of Public Health and Primary Care, University of Cambridge, United Kingdom (R.C., M.S.); School for Policy Studies, University of Bristol, United Kingdom (L.J.). Correspondence to: Dr. Rajiv Chowdhury, Senior Research Associate, Cardiovascular Epidemiology Unit, Department of Public Health and Primary Care, University of Cambridge, Cambridge CB1 8RN, United Kingdom. E-mail: [email protected] J Am Heart Assoc. 2014;3:e001195 doi: 10.1161/JAHA.114.001195. a 2014 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.