Trans fatty acids (TFA): analysis, occurrence, intake and clinical relevance.

More than one quarter of total daily calories are normally provided by fatty acids which contain at least one double bond. The usual configuration of these double bonds is the cis configuration. Trans fatty acids (TFA) are formed in technological and microbiological processes by isomerization of cis double bonds to trans double bonds. In the 1990s, there was public health concern about epidemiological studies suggesting that TFA increase the risk of coronary heart disease. High intakes of TFA may have an influence on total cholesterol and other blood parameters; but on the other hand there have been a lot of studies which have not been able to confirm these results. TFA are formed in varying amounts during the industrial hydrogenation of vegetable oils and in the first stomach of ruminants. Regular margarines contain varying contents of partially hydrogenated vegetable oils, and therefore of TFA. The main dietary TFA are the trans octadecenoic acids, which contribute to approximately 80-90 % of total TFA content in foods. The predominant isomer of milk fat is trans vaccenic acid, which is directly influenced by ruminant feeding conditions. For a reliable identification and quantification of TFA in foods and other biological matrices it is necessary to use a combination of chromatographic methods (GC-FID, GC-MS, GC-FTIR, Ag superset +-HPLC).