Dietary influences trans fatty acids

Opposing effects of certain individual fatty acids could have influenced the lack of a relationship between dietary fat and fat type with the risk of breast cancer. Well-conducted animal studies suggest that linoleic acid promotes development of mammary tumors, whereas saturated, monounsatu-rated, and trans fatty acids have little or no effect. In many cases, w-3 polyunsaturated fatty acids suppress tumor development. Conjugated linoleic acid (CLA) is the most potent anti-cancer fatty acid in that amounts of 1% or less of dietary fat can substantially inhibit the development of mammary tumors (Ip, 1997). 

Simopoulos AP, Is insulin resistance influenced by dietary linoleic acid and trans fatty acids Free Radical Biol Med 1994 17(4) 367-372. 

Trans fatty acids occur mainly in positions 1 and 3 of triacylglycerols, the predominant lipids in adipose tissue. The concentration of trans fatty acids in adipose tissue is approximately proportional to long-term dietary intake, and determination of the concentrations in storage fat is one method used to estimate trans fatty acid intake. However, this is not entirely straightforward as variation has been reported in the composition of adipose tissue obtained from different sites and depths, and factors that influence adipose tissue turnover rates such as dieting and exercise are also complicating factors. Trans-18 l isomers account for approximately 70% of the trans fatty acids found in adipose tissue, and trans-18 2 isomers (trans,trans, trans,cis, and cisytrans) account for about 20%. 

The influence of trans fatty acids on plasma lipoproteins in relation to CHD risk would thus appear to be more unfavorable than that of saturated fatty acids, as determined by the effect on the ratio of LDL to FIDL cholesterol. However, the overall magnitude of the effect would be dependent on the relative intakes of trans fatty acids and saturated fatty acids. In the UK trans fatty acids contribute about 2% of dietary energy, in contrast to saturated fatty acids which contribute about 15% dietary energy, and this needs to be considered when formulating dietary advice. The Task Force also estimated, on the same basis, that a reduction of 6% in energy from saturated fatty acids would decrease risk by 37%. 

Except for eicosanoic acid, the proportions of all fatty acids in egg yolk lipids were significantly (P < 0.01) influenced by the dietary CLA (59). The proportions of myristic, palmitic, and stearic acids, and CLA cis-9,trans- CLA and transit),cis-f2 CLA) in egg yolk lipids were increased by dietary CLA, but those of palmitoleic, oleic, linoleic, and linolenic, arachidonic acids, and DHA were decreased. These changes in fatty acid composition of yolk lipids are similar to those reported by Chamruspollert and Sell (60), although the total CLA concentration observed in the current research when a 5% CLA diet was fed (8.5-8.6%) was less than the 11.2% reported by those authors. The decrease in the concentrations of linoleic and linolenic acids in yolk lipids of hens fed CLA likely reflects the relatively low concentration of these fatty acids in the CLA source compared with soybean oil. Decreases in arachidonic acid and DHA in yolk lipids from hens fed CLA also could be related to the low concentration of dietary linoleic and linolenic acids, which serve as precursors to the formation of arachidonic acid and DHA. Another possibility is that CLA may compete with Unoleic and/or linolenic add for A6-desaturase, the rate-limiting step for the conversion of these fatty acids into arachidonic acid and/or DHA in liver microsomes (48). Feeding CLA increased the concentration of stearic acid in yolk lipids. 

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