Ruminant TFAs are often overlooked due to the abundance of literature focusing on the effects of industrially produced trans fats in different diseases. However, typically we consume 2–9% of our total fatty acid content as rTFAs (Bassett et al., 2010). Furthermore, the TRANSFAIR study estimated that as much as half of all trans fats consumed in specialty diets like the Mediterranean diet will be in the form of rTFAs (van de Vijver et al., 2000). Ruminant TFAs are found in grass grazing sheep and cattle. Therefore, sheep and cattle meats as well as dairy products (cheese, milk and butter) contain rTFAs. The major contributor within the category of rTFAs is vaccenic acid. Vaccenic acid (18:1 trans-11) constitutes 50–80% of all ruminant derived trans fats (Field et al., 2009). Conjugated linoleic acids (cLAs) complete the rest of the category. Briefly, cLAs are also found in ruminant products and are identified by two double bonds within the aliphatic chain that are separated by a single bond in between. Rumenic acid (c9t11-CLA) is an example of conjugated linoleic acids. Vaccenic acid consists of only one double bond. It is the isomer of oleic acid (18:1 trans-11) and although similar to elaidic acid, the position of the double bond in vaccenic acid (position 11 vs. position 9 in elaidic acid) plays an integral role in determining the differences between the two fatty acids. Vaccenic acid is derived from incomplete biohydrogenation of the PUFAs, linoleic acid and linolenic acid, within the gut of the ruminant animals. Specialized gut microflora known as Roseburia hominis A2-183T, Roseburia inulinivorans A2-192T and Ruminococcus obeum-like strain A2-162 produce vaccenic acid from these sources. It is therefore imperative that the differences between iTFAs and rTFAs are recognized in terms of their detrimental or positive health effects.