Linoleic acid: Between doubts and certainties

doi:10.1016/j.biochi.2013.07.012

Biochimie

Volume 96, January 2014, Pages 14-21

https://doi.org/10.1016/j.biochi.2013.07.012 Get rights and content

Highlights

•
A current overview on the metabolism of linoleic acid.
•
Biological importance of linoleic acid in physiological process.
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Consequences and pathological implications of an excess of linoleic acid.

Abstract

Linoleic acid is the most abundant polyunsaturated fatty acid in human nutrition and represents about 14 g per day in the US diet. Following the discovery of its essential functions in animals and humans in the early 1920's, studies are currently questioning the real requirement of linoleic acid. It seems now overestimated and creates controversy: how much linoleic acid should be consumed in a healthy diet? Beyond the necessity to redefine the dietary requirement of linoleic acid, many questions concerning the consequences of its excessive consumption on human health arise. Linoleic acid is a direct precursor of the bioactive oxidized linoleic acid metabolites. It is also a precursor of arachidonic acid, which produces pro-inflammatory eicosanoids and endocannabinoids. A majority of the studies on linoleic acid and its derivatives show a direct/indirect link with inflammation and metabolic diseases. Many authors claim that a high linoleic acid intake may promote inflammation in humans. This review tries to (i) highlight the importance of reconsidering the actual requirement of linoleic acid (ii) point out the lack of knowledge between dietary levels of linoleic acid and the molecular mechanisms explaining its physiological roles (iii) demonstrate the relevance of carrying out further human studies on the single variable linoleic acid.

Section snippets

Consequences of a deficiency in linoleic acid

The first reports dating back to the 1920's claimed that dietary fats contained two vitamin-like substances, soon identified as linoleic acid (18:2 n-6) and α linolenic acid (18:3 n-3), precursors respectively of the n-6 and n-3 fatty acid families (Fig. 1). The first demonstration of essential requirement for linoleic acid in animal diet was obtained by Burr and Burr in 1929–30 [8], [9]. They showed in the rat that the single linoleic acid consumption was able to prevent or correct the

High levels of linoleic acid can reduce the conversion of α linolenic acid into highly unsaturated n-3 fatty acids

In the liver, long chain PUFA are synthetized from both dietary linoleic and α linolenic acids according to a similar multi step pathway including fatty acid desaturations and elongations (Fig. 1). The Δ6 desaturase (FADS2) catalyzes the first step of this common pathway and is described as the rate limiting enzyme [24]. Thus, linoleic acid shares the same enzymatic system and can compete with α linolenic acid conversion [25], [26]. This competition also occurs with oleic acid, which is another

Human studies are rare but their results are promising

Very few studies have been designed to understand how dietary linoleic acid directly affects inflammatory status in humans. Among these studies, Ferruci and al. [73], have investigated the relationship between plasma polyunsaturated fatty acids and circulating inflammatory markers. In this epidemiological study, samples were obtained from 1300 subjects in Italy. The data did not show any significant relationship between n-6 total fatty acids in the plasma and the pro-inflammatory circulating

Conclusion

N-6 polyunsaturated fatty acids and their precursor, linoleic acid, are essential for many functions. Their derivatives are involved in complex metabolic pathways.

On one hand, in vitro studies have clearly demonstrated the links between the pro-inflammatory properties of linoleic acid and metabolic diseases. On the other hand, human studies do not validate these links but we have to keep in mind that an excess of linoleic acid in the diet may increase the total mortality [65]. Even if linoleic

Acknowledgments

The authors thank Jane Wilson for her English revision of the manuscript.

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Mini-reviewLinoleic acid: Between doubts and certainties

Highlights

Abstract

Section snippets

Consequences of a deficiency in linoleic acid

High levels of linoleic acid can reduce the conversion of α linolenic acid into highly unsaturated n-3 fatty acids

Human studies are rare but their results are promising

Conclusion

Acknowledgments

J. Nutr.

Prostaglandins Other Lipid Mediat.

Prostaglandins Leukot. Essent. Fatty Acids

J. Biol. Chem.

Prog. Chem. Fats Others Lipids

Prog. Lipid. Res.

J. Lipid. Res.

J. Nutr.

Biochim. Biophys. Acta

J. Biol. Chem.

Prostaglandins Leukot. Essent. Fatty Acids

J. Lipid. Res.

J. Biol. Chem.

Biochimie

Prostaglandins Leukot. Essent. Fatty Acids

Prostaglandins Leukot. Essent. Fatty Acids

Am. J. Clin. Nutr.

Prostaglandins Leukot. Essent. Fatty Acids

Early Hum. Dev.

Biochem. Biophys. Res. Commun.

FEBS Lett.

Prostaglandins Leukot. Essent. Fatty Acids

Prostaglandins Leukot. Essent. Fatty Acids

Neurobiol. Aging

Chem. Phys. Lipids

Cell

Chem. Phys. Lipids

J. Biol. Chem.

Atherosclerosis

Biochim. Biophys. Acta

Mod. Pathol.

Prostaglandins Other Lipid Mediat.

Am. J. Clin. Nutr.

Essentiality of fatty acids

Lipids

Bioactive dietary long-chain fatty acids: emerging mechanisms of action

Br. J. Nutr.

The omega-6/omega-3 fatty acid ratio, genetic variation, and cardiovascular disease

Asia Pac. J. Clin. Nutr.

Omega-6 fatty acids and risk for cardiovascular disease: a science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention

Circulation

A new deficiency disease produced by the rigid exclusion of fat from the diet

J. Biol. Chem.

Mini-review
Linoleic acid: Between doubts and certainties