Perspectives on Conjugated Linoleic Acid Research
Lister Hill Auditorium
Bethesda, Maryland
May 15-16, 2002
Abstract
The Origin of CLA
Dale E. Bauman
Cornell University
Department of Animal Science
The CLA in foods derived from ruminants relates to the biohydrogenation of unsaturated fatty acids by rumen bacteria and most of the work has involved dairy cows and milk fat. cis-9, trans-11 CLA is the predominant isomer representing 75 to 80% of total CLA. This isomer is formed as an intermediate in the biohydrogenation of linoleic acid. Although rumen production is the source for a portion of milk fat CLA, the major source is endogenous synthesis. Between 70 to 95% of the cis-9, trans-11 CLA in milk fat originates by endogenous synthesis via ∆9-desaturase from trans-11 C18:1, another biohydrogenation intermediate. In ruminants, ∆9-desaturase activity is high in adipose tissue of growing animals, and in mammary tissue and adipose tissue of lactating animals; mRNA and protein for this enzyme are negligible in liver. The second most prevalent CLA isomer in milk fat is trans-7, cis-9 and it originates almost exclusively from endogenous synthesis involving ∆9-desaturase and trans-7 C18:1 produced in the rumen. Other CLA isomers in milk fat, which are present in much lower quantities, originate from rumen biohydrogenation. Under certain dietary conditions, a portion of linoleic acid biohydrogenation in the rumen can involve an isomerization of the cis-9 double bond to form trans-10, cis-12 CLA. These diets are associated with a change in the rumen environment, an increase in milk fat content of trans-10, cis-12 CLA, and a marked reduction in milk fat secretion. Overall, milk fat content of CLA is largely dependent on rumen outflow of trans-11 C18:1 and tissue activity of ∆9-desaturase; both of these variables can be markedly affected by diet and vary substantially among individuals. Thus, by manipulating the diet and through genetic selection, the CLA content of foods derived from ruminants can be altered. Documentation of CLA Intake in Humans; Michelle Kay McGuire and Mark A. McGuire
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