Current Insights into the Effects of Dietary α-Linolenic Acid Focusing on Alterations of Polyunsaturated Fatty Acid Profiles in Metabolic Syndrome

The plant-derived α-linolenic acid (ALA) is an essential n-3 acid highly susceptible to oxidation,
present in oils of flaxseeds, walnuts, canola, perilla, soy, and chia. After ingestion, it can be
incorporated in to body lipid pools (particularly triglycerides and phospholipid membranes), and
then endogenously metabolized through desaturation, elongation, and peroxisome oxidation to
eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), with a very limited efficiency
(particularly for DHA), beta-oxidized as an energy source, or directly metabolized to C18-
oxilipins. At this moment, data in the literature about the effects of ALA supplementation on
metabolic syndrome (MetS) in humans are inconsistent, indicating no effects or some positive
effects on all MetS components (abdominal obesity, dyslipidemia, impaired insulin sensitivity
and glucoregulation, blood pressure, and liver steatosis). The major effects of ALA on MetS
seem to be through its conversion to more potent EPA and DHA, the impact on the n-3/n-6 ratio,
and the consecutive effects on the formation of oxylipins and endocannabinoids, inflammation,
insulin sensitivity, and insulin secretion, as well as adipocyte and hepatocytes function. It is
important to distinguish the direct effects of ALA from the effects of EPA and DHA metabolites.
This review summarizes the most recent findings on this topic and discusses the possible
mechanisms.