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Natural Trans Fats

There are substantial differences between the natural trans fats in fats from ruminants (cows, sheep, goats) and the trans fats in industrially produced vegetable fats and oils. The hydrogenation process is radically different, as are the types and amounts of trans fats created.

The hydrogenation process

Unsaturated fats in plants eaten by ruminant animals undergo biohydrogenation via bacteria found in the rumen of the animal.1 This process is natural and catalyzed by bacterial enzymes at normal body temperature and under normal body pressure.1

In contrast, industrial trans fats are formed when liquid vegetable oil is converted into a solid through the chemical process of hydrogenation. This process is initiated by metal catalysts under enormous pressure at very high temperatures. Before they became widespread in the late 1940s, many of these trans fats had never before been encountered in nature or existed only in trace amounts.2,3

Typical distribution of isomers in natural and industrial trans fats*

Table 1: Typical Distribution of Ruminant 18:1 Trans Fatty Acids4

Typical Distribution of Ruminant

Table 2: Typical Distribution of Industrial 18:1 Trans Fatty Acids4

Typical Distribution of Industrial

*The majority of trans fat in ruminant fats, and to a lesser extent in partially hydrogenated vegetable fats and oils, are isomers of the monounsaturated fat oleic acid (18:1).5

As these graphs illustrate, most of the same isomers are found in naturally occurring and industrial trans fats. However, their vastly different distribution changes their effects.4,5

In fact, the trans fat in partially hydrogenated vegetable fats have been shown to increase the risk of heart disease.4,6 Studies to date suggest the same cannot be said for those from ruminants.4,6

Cis and trans double bonds

Double Bond

Did you know...

  • Naturally occurring trans fats have been in the food supply since animals were first domesticated to provide food—at least 10,000 years ago;
  • Vaccenic acid, the predominant isomer in dairy and beef trans,4 is partially converted by the body into conjugated linoleic acid (CLA),7 a potential inhibitor of breast cancer.8-10


  1. Holmqvist O. Trans fatty acids in hardened vegetable oils. (Letter to the Editors). Atherosclerosis 1996;120:245-246.
  2. Willett WC and Ascherio A. Trans fatty acids: are the effects only marginal? Am J Pub Health 1994;84:722-724.
  3. Ratnayake WHN and Chen ZY. Trans fatty acids in Canadian breast milk and diet. In: Development and Processing of Vegetable Oils for Human Nutrition. R Przybylski and BE McDonald (eds.). Ch. 3:20-35. Champaign, IL: AOCS Press, 1995.
  4. Stender S and Dyerberg J. Influence of trans fatty acids on health. Ann Nutr Metab 2004;48:61-66.
  5. Lock AL et al. The biology of trans fatty acids: implications for human health and the dairy industry. Aust J Dairy Technol 2005;60:3-12.
  6. Ascherio A et al. Trans fatty acids and heart disease. N Engl J Med 1999;340:1994-1996.
  7. Turpeinen AM et al. Bioconversion of vaccenic acid to conjugated linoleic acid in humans. Am J Clin Nutr 2002;76:504-510.
  8. Parodi PW. Milk fat conjugated linoleic acid: can it help prevent breast cancer? Proc Nutr Soc N Z 1997;22:137-149.
  9. Aro A et al. Inverse association between dietary and serum conjugated linoleic acid and risk of breast cancer in postmenopausal women. Nutr Cancer 2000;38:151-157.
  10. McCann SE et al. Dietary intake of conjugated linoleic acids and risk of premenopausal and postmenopausal breast cancer. Western New York Exposures and Breast Cancer Study (Web Study). Cancer Epidemiol Biomarkers Prev 2004;13:1480-1484.

Keywords: trans fat

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