Trans fatty acids and cholesterol levels: an evidence map of the available science

Authors: LISKA, DEANN - Biofortis Clinical Research; COOK, CHAD - Biofortis Clinical Research; WANG, DING DING - Biofortis Clinical Research; GAINE, P. COURTNEY - International Life Sciences Institute (ILSI); Baer, David

Submitted to: Food and Chemical Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2016
Publication Date: 7/7/2016
Citation: Liska, D.J., Cook, C.M., Wang, D., Gaine, P., Baer, D.J. 2016. Trans fatty acids and cholesterol levels: an evidence map of the available science. Food and Chemical Toxicology. 98(B):269-281. https://doi.org/10.1016/j.fct.2016.07.002.
DOI: https://doi.org/10.1016/j.fct.2016.07.002

Interpretive Summary: Trans fatty acids (TFA) are produced during the partial hydrogenation of vegetable and other oils. The process was developed to increase stability of oils high in polyunsaturated fatty acids and hence prone to oxidation. Moreover, this process improves the functional properties of oils for specific applications such as baking. In fact, partially hydrogenated oils (PHO) became a predominant source of industrially trans fatty acid intake when margarines were promoted over saturated fat-containing oils like butter and lard in the 1970s-80s. High intakes of trans fatty acids from these industrial sources (iTFA) have been shown to increase the concentration of circulating low-density lipoprotein (LDL) cholesterol, and increased LDL cholesterol is associated with increased risk of coronary heart disease risk (CHD). However, in 2006 the Food and Drug Administration required that nutrition labels must declare the amount of trans fatty acids in foods, and use of partially hydrogenated oils, and subsequently intakes of iTFA, have decreased substantially from averages intakes of >3% of energy prior to 2003 to current levels of <1% of energy. Much of the published data upon which the relationship of iTFA to increased LDL-cholesterol is based on the higher and outdated level of TFA intakes. Based on these studies, and assuming that a linear relationship exists between iTFA and LDL-cholesterol, the Food and Drug Administration has published a notice indicating that no level of TFA intake is safe. Controversy has arisen over this notice and, specifically, on whether science is available for an evidence-based assessment of iTFA at levels of intakes representative of the current average consumption by the U.S. population. This current study was conducted to identify and characterize the full body of science available for an evidence-based assessment of the relationship between LDL-cholesterol and iTFA at low intake levels. In particular, this study used state-of-the-art evidence mapping approache to provide a thorough review of published literature that examined effects of iTFA containing oil(s) or isolated iTFA source(s) substituted for cis-monounsaturated fatty acids or saturated fatty acids on LDL-cholesterol. A total of 32 independent clinical trials that included at least one intervention or control group with iTFA at =3% of energy were found. Review of these studies indicated that a wide range of oils and interventions were used. Moreover, few data points were found for iTFA at <3% of energy, with the majority of low level exposures actually representing control group interventions with non-PHO oils. Furthermore, a lack of consistency was observed in the utilization of studies across the most influential reviews on iTFA and cholesterol upon which policy recommendations have been based. Our findings suggest the totality of evidence related to iTFA intake and corresponding impact on LDL- cholesterol has not been uniformly considered. In addition, it appears few dose-response data points are available to assess the relationship of low levels of iTFA, particularly from PHO exposure, and LDL-cholesterol. In fact, based on the collective evidence, it appears that current average iTFA intakes have not been studied as the primary dietary intervention under controlled conditions. These data are of interest to public health professionals, the food industry, regulatory agencies, and consumers interested in reducing their risk for coronary heart disease through dietary modification.

Technical Abstract: High intakes of industrial trans fatty acids (iTFA) increase circulating low density lipoprotein cholesterol (LDL-C) levels, which has implicated iTFA in coronary heart disease (CHD) risk. Published data on iTFA and LDL-C, however, represent higher intake levels than the U.S. population currently consume. This study used state-of-the-art evidence mapping approaches to characterize the full body of literature on LDL-C and iTFA at low intake levels. A total of 32 independent clinical trials that included at least one intervention or control group with iTFA at =3%en were found. Findings indicated that a wide range of oils and interventions were used, limiting the ability to determine an isolated effect of iTFA intake. Few data points were found for iTFA at <3%en, with the majority of low-level exposures actually representing control group interventions containing non-partially hydrogenated (PHO) oils. Further, it appears that few dose-response data points are available to assess the relationship of low levels of iTFA, particularly from PHO exposure, and LDL-C. Therefore, limited evidence is available to determine the effect of iTFA at current consumption levels on CHD risk.