Linoleic acid (LA) is the only essential omega-6 fatty acid and must be obtained from the diet. From LA, other omega-6s can be created using elongase and desaturase enzymes. LA contains 18 carbons, with 2 double bonds, the first of which is at the 6th carbon position (18:2n6). LA is found in nuts and vegetable oils (corn, soybean, canola, sunflower, etc.) as well as most meats. When the double bonds of LA are arranged differently, the term conjugated LA (CLA) is used. Although technically CLA can be termed a trans-fat, a natural type of CLA can be obtained in the dietary intake of meat and milk from ruminant animals. There are many isomers of CLA – some beneficial and others are not as well defined. There is some controversy regarding how much LA is needed from the diet for adequacy. Although LA is needed to synthesize downstream fatty acids, it may lead to increased inflammatory fatty acid production. Several studies show that LA lowers blood cholesterol levels and improves all-cause mortality However, their current role in atherosclerosis and cardiometabolic disease are being revisited. There is difficulty in differentiating the biological effects of LA from arachidonic acid in health and disease. In fact, it has been shown that LA is the most abundant fatty acid found in LDL and is one of the first fatty acids to oxidize. Studies are showing that LA promotes oxidative stress, oxidized LDL, and may be a major dietary cause of cardiovascular disease, especially when consumed via industrial vegetable oils.
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- Subbaiah PV, Sircar D, Aizezi B, Mintzer E. Differential effects of conjugated linoleic acid isomers on the biophysical and biochemical properties of model membranes. Biochimica et biophysica acta. 2010;1798(3):506-514.
- Jandacek RJ. Linoleic acid: a nutritional quandary. Paper presented at: Healthcare2017
- Salas-Salvado J, Marquez-Sandoval F, Bullo M. Conjugated Linoleic Acid Intake In Humans: A Systematic Review Focusing on Its Effect on Body Composition, Glucose, and Lipid Metabolism. Critical Reviews in Food Science and Nutrition. 2006;46(6):479-488.
- Li J, Guasch-Ferre M, Li Y, Hu FB. Dietary intake and biomarkers of linoleic acid and mortality: systematic review and meta-analysis of prospective cohort studies. The American journal of clinical nutrition. 2020.
- Hegazy M, Elsayed NM, Ali HM, Hassan HG, Rashed L. Diabetes Mellitus, Nonalcoholic Fatty Liver Disease, and Conjugated Linoleic Acid (Omega 6): What Is the Link? Journal of Diabetes Research. 2019;2019:5267025.
- Smedman A, Vessby B. Conjugated linoleic acid supplementation in humans--metabolic effects. Lipids. 2001;36(8):773-781.
- DiNicolantonio JJ, O Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Heart. 2018;5(2):e000898.
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Linoleic acid deficiency is rare, especially give current dietary trends which include excess vegetable oils. However, lack or decreased intake of foods containing LA can contribute to lower levels. Additionally, a SNP in delta-6-desaturase may potentially alter the enzyme function and promote downstream metabolism. Essential linoleic acid deficiencies have been mainly associated with skin conditions and impaired growth and development. Low levels of LA may contribute to impaired wound healing since it has been found to modulate a cellular response in wound healing by increasing the migration and functions of inflammatory and endothelial cells, and by inducing angiogenesis at the wound site.
Elevations are seen with high dietary fat intake (especially vegetable oils), or with supplementation of CLA. The delta-6-desaturase enzyme converts LA to downstream fatty acids. Lack of vitamin and mineral cofactors, or a SNP in the enzyme may slow its ability to covert and elevate LA levels. Additionally, there is competition with the omega-3 fatty acids for use of this enzyme which may contribute to elevated levels depending on availability. High levels of LA are associated with obesity, inflammatory conditions such as IBD, various cancers, cardiovascular disease, altered cognition, and brain development.
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