Mini-reviewLinoleic acid: Between doubts and certainties
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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