152 JOURNAL OF BIOSCIENCE AND BIOENGINEERING © 2005, The Society for Biotechnology, Japan Vol. 100, No. 2, 152–157. 2005 DOI: 10.1263/jbb.100.152 REVIEW Conjugated Fatty Acids in Food and Their Health Benefits Koji Nagao 1 and Teruyoshi Yanagita 1 * Laboratory of Nutrition Biochemistry, Department of Applied Biological Sciences, Saga University, 1 Honjo, Saga 840-8502, Japan 1 Received 28 March 2005/Accepted 25 April 2005 Conjugated fatty acids (CFAs) are a mixture of positional and geometric isomers of polyunsatu- rated fatty acids with conjugated double bonds. Reports indicate that CFAs have potent beneficial effects, including antitumor, antiobese, antiatherogenic and antidiabetic activities. The molecules have also been shown to prevent the onset of hypertension. Recent reports suggest that each CFA isomer has different functions, for example the 10trans,12cis isomer of conjugated linoleic acid (CLA) has anticarcinogenic, antiobese and antidiabetic effects, whereas the 9cis,11trans-CLA iso- mer exerts an anticancer effect. Although it would be interesting to know the effects of CFAs on humans, there are only few reports concerning the anticancer and antiobese effects of CLA in hu- mans. More detailed evaluations of the physiological bioactivities of CFA isomers on lifestyle-re- lated diseases in humans and animals will be of great interest in future studies. [Key words: conjugated fatty acids, cancer, obesity, hypertension, lifestyle-related diseases] Lifestyle-related diseases, such as obesity, hyperlipidemia, arteriosclerosis, diabetes mellitus and hypertension, are wide- spread and increasingly prevalent in industrialized coun- tries. Because of the rapid increase in the number of elderly people, these diseases are important medically and socio- economically. It is also assumed that one-third of human cancers is associated with dietary habits and lifestyle (1). Although the pathogenesis of lifestyle-related diseases is complicated and the precise mechanisms underlying their development have not yet been elucidated, it has been noted that the quality of dietary lipids could be an important mod- ulator in terms of the morbidity and mortality of these dis- eases (2). In particular, polyunsaturated fatty acids (PUFAs), such as linoleic acid (18:2, n-6), α-linolenic acid (LNA, 18 : 3, n-3) and arachidonic acid (20 : 4, n-6), are very impor- tant for the maintaining biofunctions in mammalians as es- sential fatty acids (3). In addition, it has been reported that the consumption of n-3 highly unsaturated fatty acids, such as eicosapentaenoic acid (EPA, 20:5, n-3) and docosahex- aenoic acid (DHA, 22 : 6, n-3), correlates with a reduced risk of cancer and cardiovascular disease in human and animal studies (4, 5). At present, conjugated fatty acids (CFAs) have attracted considerable attention because of their potentially beneficial biologic effects of attenuating lifestyle-related diseases (6– 8). CFAs refer to a mixture of positional and geometric iso- mers of PUFAs with conjugated double bonds. Theoreti- cally, a number of CFA isomers are possible, with multiple combinations of numerical, positional and geometrical con- figurations of conjugation in double bonds (Fig. 1). NATURAL SOURCES AND INDUSTRIAL PRODUCTION OF CFAs Conjugated linoleic acid (CLA), the CFA form of linoleic acid, has been detected in milk fat, cheese and ruminant meat (9). The 9cis,11trans (9c,11t)-CLA isomer is naturally produced through the biohydrogenation of unsaturated fatty acids by the rumenal bacterium Butyrvibrio fibrisolvens in ruminants, such as cows, sheep, goats and camels (10, 11). The daily intake of CLA has been calculated for various countries and estimated at several hundred mg in a typical diet (12–16). There are also other types of CFA in some * Corresponding author. e-mail: yanagitt@cc.saga-u.ac.jp phone/fax: +81-(0)952-28-8782 FIG. 1. Structure of conjugated fatty acid isomers.