Conjugated linoleic acids

As conjugated linoleic acids (engl. Conjugated linoleic acids or abbreviated CLA ) is a group of doubly unsaturated fatty acids , with conjugated double bonds conjuenic to the linoleic acid referred to. In addition to the cis-trans isomers , this group also includes positional isomers with conjugated double bonds . Certain isomers of this group are particularly found in meat and dairy products from ruminants . The most common isomer is cis-9, trans-11-CLA, which is a trans fatty acid .

Structure of the CLA isomers

Positional isomers
Linoleic acid	cis - cis fatty acid	Unconjugated double bonds
Octadeca-9c, 12c-dienoic acid		—C = C — C — C = C—
Linoleic acid derivatives	cis - trans fatty acids	Conjugated double bonds
Octadeca-9c, 11t-dienoic acid (rumic acid, 9,11-CLA)		—C = C — C = C—
Octadeca-10t, 12c-dienoic acid (10,12-CLA)		—C = C — C = C—
Stearic acid	saturated fat	no double bond
Octadecanoic acid		—C — C — C — C — C—

education

Contents in food

Food	CLA in g / kg fat
milk	2-30
butter	9.4-11.9
cheese	0.6-7.1
Processed cheese	3.2-8.9
ice	4.9
sour cream	7.5
yogurt	5.1-9.0
Beef, fried	3.1-9.9
vegetable oils, marine animal oils	0.2-0.5

CLA is in ruminants rumen as an intermediate in the biological hydrogenation of linoleic acid to stearic acid by linoleic acid isomerase of rumen bacterium Butyrivibrio fibrisolvens formed. The substrate composition in the rumen influences the supply of intermediate and end products of biological hydrogenation. This affects the level of CLA in milk. Most of the CLA isomers are in the cis -9, trans -11 form. The conversion efficiency of CLA to milk fat is influenced by the presence of various CLA isomers. Vegetable fats are rich in linoleic and linolenic acids , which leads to increased CLA production in the rumen and mammary glands . The proportion of the main isomer cis -9, trans -11-CLA is increased in particular in the case of grass-rich (low-concentrate) feeding. It is scientifically discussed whether an additional increase in feeding on species-rich poor pastures , e.g. B. in the Alps, so in Alpine milk takes place. However, this does not appear to be the case.

Fat and milk cells of ruminants can form cis -9, trans -11-CLA from trans -11-18: 1- vaccenic acid (trans-vaccenic acid) by desaturation of the vaccenic acid. In humans, too, CLA can be formed by isomerization from linoleic acid, induced by anaerobic microbial activities in the intestine or by free radicals . Furthermore, they can also arise from denaturation from trans-vaccenic acid. Certain tissues in the human body therefore contain small amounts of CLA.

Effects

The European Food Safety Authority (EFSA) has scientifically examined positive health claims for conjugated linoleic acids in the course of Article 13 of Regulation (EC) No. 1924/2006 (Health Claims) . In 14 of 16 intervention studies on humans, no significant effect on body weight was found. An effect on the Lean Body Mass (LBM), the lean body mass ( lean mass), could not be shown either. The EFSA does not consider any influence on insulin sensitivity , the sensitivity of the insulin receptors to insulin, to be proven. An antioxidant effect , which protects DNA , proteins and lipids from oxidative damage , could not be proven either. A stimulation of the immune system by protective antibodies against pathogens could not be proven either.

See also

Conjugated linolenic acids

Individual evidence

1. ^ Hans-Dieter Belitz , Werner Grosch , Peter Schieberle : Textbook of food chemistry . 6th completely revised edition. Springer, Berlin / Heidelberg 2008, ISBN 978-3-540-73201-3 , p. 165 , doi : 10.1007 / 978-3-540-73202-0 .
2. ^ Kraft et al .: Differences in CLA isomer distribution of cow's milk lipids. In: Lipids No. 38 (6), 2003, p. 657 ff, PMID 12934676 .
3. ↑ Leiber et al .: A study on the causes for the elevated n-3 fatty acids in cows' milk of alpine origin. In: Lipids No. 40 (2), 2005, p. 192 ff, PMID 15884768 .
4. ↑ Scientific Opinion on the substantiation of health claims related to conjugated linoleic acid (CLA) isomers and contribution to the maintenance or achievement of a normal body weight (ID 686, 726, 1516, 1518, 2892, 3165), increase in lean body mass (ID 498, 731), increase in insulin sensitivity (ID 1517), protection of DNA, proteins and lipids from oxidative damage (ID 564, 1937), and contribution to immune defenses by stimulation of production of protective antibodies in response to vaccination ( ID 687, 1519) pursuant to Article 13 (1) of Regulation (EC) No 1924/2006 In: EFSA Journal. 8 (10), 2010, p. 1794, doi : 10.2903 / j.efsa.2010.1794 .