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Trans fatty acids are fatty acids that have a trans configuration on the unsaturated portion instead of a cis configuration. They can occur naturally in some animal fats, but are more often formed by transformation from unsaturated cis-oriented fatty acids. TFAs are not produced as a final product by any metabolic process in humans, so all TFAs found in blood and tissue come from food sources as follows: by bacterial biotransformation of unsaturated fatty acids in ruminant rumen, industrial hydrogenation, and deodorization of unsaturated plant (or fish) ) and heat treatment of the oil at high temperatures.