ARS | Publication request: Effects of ruminant trans fatty acids on cardiovascular disease and cancer: a comprehensive review of epidemiological, clinical, and mechanistic studies

Submitted to: Advances in Lipid Research
Publication Type: Review Article
Publication Acceptance Date: May 18, 2012
Publication Date: July 1, 2011
Citation: Gebauer, S.K., Chardigny, J., Proctor, S.D., Jacobsen, M.U., Lamarche, B., Lock, A.L., Baer, D.J. 2011. Effects of ruminant trans fatty acids on cardiovascular disease and cancer: a comprehensive review of epidemiological, clinical, and mechanistic studies. Advances in Nutrition. 2:332-354.

Interpretive Summary: Our food contains dietary trans fatty acids (TFA) from two major sources. First, dietary TFA are produced during the partial hydrogenation of vegetable oils, a chemical process that stabilizes oils. In addition to this source of dietary TFA, ruminant animals, such as cattle, sheep, and goats, produce dietary TFA during the digestion of their foods. There are differences in the type of dietary TFA produced during industrial processing of vegetables oils and those produced by animals. We review the literature of these different sources of TFA with respect to their role in cardiovascular disease (CVD) and cancer, which are the leading causes of death in the United States. Some studies suggest that there is a positive association with heart disease risk between consumption of industrial but not ruminant sources of TFA. Associations between intake of industrial sources of TFA and cancer have been less consistent, and associations between ruminant TFA intake and cancer have not been studied in depth. Small studies have been conducted to establish a cause and effect relationship between the two different sources of TFA and heart disease, but results from these studies have been inconclusive, in part because these studies may be too small. Clinical studies have not been conducted investigating the cause and effect relationship between the two sources of TFA and cancer risk for certain cancers. Some but not all studies designed to understand cellular metabolism have demonstrated that ruminant sources of TFA may reduce cell growth and or tumor metabolism. Some of the ruminant TFA reportedly affects initiation, promotion, and metastasis of several cancers in experimental animal models. Further research is needed to determine the effects of the ruminant sources of TFA in humans. Since many studies have used amounts of these sources that are not realistically attainable via diet, further clinical studies are warranted.

Technical Abstract: There are two predominant sources of dietary trans fatty acids in the food supply, those formed during the industrial partial hydrogenation of vegetable oils (iTFA) and those formed by biohydrogenation in ruminants (rTFA), including vaccenic acid and (VA) and rumenic acid [RA, a conjugated linoleic acid (CLA)]. Some epidemiological studies suggest that a positive association with coronary heart disease risk only exists between TFA isomers generated by industrial means and not with rTFA. Associations between intake of iTFA and cancer have been less consistent, and associations between rTFA intake and cancer have not been well-studied. Small clinical studies have been conducted to establish cause and effect relationships between these different sources of TFA and biomarkers or risk factors for cardiovascular disease, with inconclusive results. The lack of detection of treatment effects reported in some studies may be due to insufficient statistical power. Clinical studies have not been conducted investigating the cause and effect relationship between iTFA and rTFA intake and risk for cancers. Some but not all mechanistic studies have demonstrated that VA may reduce cell growth and/or tumor metabolism. CLA reportedly affects initiation, promotion, and metastasis of several cancers in experimental animal models. Further research is needed to determine the effects of VA and RA in humans. Since many studies have used doses of rTFA that are not realistically attainable via diet, further clinical studies are warranted.