Trans fatty acids: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Trans fatty acids: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Trans fatty acids are unsaturated fatty acids whose double bond is in the trans position; they arise from fat hardening and from rumen bacteria. The body absorbs them like other fatty acids, builds them into cell membranes and breaks them down by beta-oxidation.

The pathway step by step

1. Unsaturated fatty acid → Trans fatty acids Hydrogenation, rumen · Nickel (industrial), Rumen bacteria When fat is partially hydrogenated or converted by rumen bacteria, the double bond flips into the trans position. The chain becomes straighter, similar to a saturated fatty acid. Source 1, 2
2. Trans fatty acids → Chylomicrons Lipases · Bile acids In the gut, lipases split dietary fats. The fatty acids are reassembled in the gut wall and released as chylomicrons via the lymph into the blood. Source 1
3. Chylomicrons → Membrane fatty acids Acyltransferases Acyltransferases build fatty acids into the phospholipids of cell membranes. Trans fatty acids end up there too; in the laboratory they are measured in the membrane of red blood cells. Source 4
4. Acyl-CoA → Rumenic acid (CLA) Δ9-desaturase · NADH, oxygen Δ9-desaturase inserts another double bond. In this way part of the vaccenic acid, the trans fatty acid from the rumen, becomes rumenic acid. Source 3
5. Acyl-CoA → Beta-oxidation Carnitine shuttle · Carnitine The carnitine shuttle brings the fatty acid into the mitochondrion. There the chain is dismantled piece by piece. For elaidic acid this breakdown remains measurably incomplete. Source 5
6. Beta-oxidation → Acetyl-CoA β-oxidation enzymes · FAD, NAD⁺ Each round of beta-oxidation yields acetyl-CoA plus the electron carriers FADH₂ and NADH. Acetyl-CoA enters the citric acid cycle. Source 5

Cofactors in this pathway

• Carnitine — Carries the activated fatty acid into the mitochondrion via the carnitine shuttle Source 5In the ORY catalogue as a laboratory value: Carnitin
• Riboflavin (vitamin B2) — As FAD, cofactor of the acyl-CoA dehydrogenases of beta-oxidation Source 5
• Niacin (NAD⁺) — NAD⁺ accepts electrons in every round of beta-oxidation Source 5In the ORY catalogue as a laboratory value: NAD⁺ (Nicotinamidadenindinukleotid)
• Pantothenic acid (coenzyme A) — Building block of coenzyme A, which activates the fatty acid before conversion Source 5
• Iron — Di-iron centre of Δ9-desaturase Source 6In the ORY catalogue as a laboratory value: Eisen
• Bile acids — Disperse dietary fat into fine droplets on which lipases act Source 1In the ORY catalogue as a laboratory value: Gallensäuren (Stuhl)
• Magnesium — Forms the complex with ATP that acyl-CoA synthetase uses for activation Source 7In the ORY catalogue as a laboratory value: Magnesium

Sources

1. Tvrzicka E, Kremmyda LS, Stankova B et al. Fatty acids as biocompounds: their role in human metabolism, health and disease — a review. Part 1: classification, dietary sources and biological functions. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub 2011 · PubMed 21804620
2. Or-Rashid MM, Wright TC, McBride BW. Microbial fatty acid conversion within the rumen and the subsequent utilization of these fatty acids to improve the healthfulness of ruminant food products. Appl Microbiol Biotechnol 2009 · PubMed 19685048
3. Kuhnt K, Kraft J, Moeckel P et al. Trans-11-18:1 is effectively Delta9-desaturated compared with trans-12-18:1 in humans. Br J Nutr 2006 · PubMed 16571155
4. Emken EA, Rohwedder WK, Dutton HJ et al. Incorporation of deuterium-labeled cis- and trans-9-octadecenoic acids in humans: plasma, erythrocyte, and platelet phospholipids. Lipids 1979 · PubMed 459721
5. Yu W, Liang X, Ensenauer RE et al. Leaky beta-oxidation of a trans-fatty acid: incomplete beta-oxidation of elaidic acid is due to the accumulation of 5-trans-tetradecenoyl-CoA and its hydrolysis and conversion to 5-trans-tetradecenoylcarnitine in the matrix of rat mitochondria. J Biol Chem 2004 · PubMed 15466478
6. Shen J, Wu G, Pierce BS et al. Free ferrous ions sustain activity of mammalian stearoyl-CoA desaturase-1. J Biol Chem 2023 · PubMed 37290533
7. de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev 2015 · PubMed 25540137

Related pathways

• APOE — chylomicrons
• Carnitine — acyl-coa
• Cholesterol and lipoproteins — chylomicrons
• Triglycerides — chylomicrons
• Vitamin E — chylomicrons

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
Legal notice Privacy policy All biomarkers