By: Sala-Vila A, Fleming J, Kris-Etherton P, Ros E.

Given the evidence of the health benefits of plant-based diets and long-chain n-3 fatty acids, there is keen interest in better understanding the role of alpha-linolenic acid (ALA), a plant-derived n-3 fatty acid, on cardiometabolic diseases and cognition. There is increasing evidence for ALA largely based on its major food sources (i.e., walnuts and flaxseed); however, this lags behind our understanding of long-chain n-3 fatty acids. Meta-analyses of observational studies have shown that increasing dietary ALA is associated with a 10% lower risk of total cardiovascular disease and a 20% reduced risk of fatal coronary heart disease. Three randomized controlled trials (AlphaOmega trial, Prevención con Dieta Mediterránea [PREDIMED] trial, and Lyon Diet Heart Study) all showed benefits of diets high in ALA on cardiovascular-related outcomes, but the AlphaOmega trial, designed to specifically evaluate ALA effects, only showed a trend for benefit. Randomized controlled trials have shown that dietary ALA reduced total cholesterol, low-density-lipoprotein cholesterol, triglycerides, and blood pressure, and epidemiological studies and some trials also have shown an anti-inflammatory effect of ALA; which collectively account for, in part, the cardiovascular benefits of ALA. A meta-analysis reported a trend toward diabetes risk reduction with both dietary and biomarker ALA. For metabolic syndrome and obesity, the evidence for ALA benefits is inconclusive. The role of ALA in cognition is in the early stages but shows promising evidence of counteracting cognitive impairment. Much has been learned about the health benefits of ALA and with additional research we will be better positioned to make strong evidence-based dietary recommendations for the reduction of many chronic diseases.

Published: February 16, 2022, in Advances in Nutrition

α-Linolenic acid from plant sources

α-Linolenic acid makes a significant contribution to the fatty acids within green leafy tissues of plants, typically comprising over 50 % of the fatty acids present. This is because α-linolenic acid is a key component of the membranes of thylakoids within chloroplasts. However, green leaves are not rich sources of fat so they are not major dietary sources of fatty acids including α-linolenic acid. α-Linolenic acid is found in significant amounts in several seeds, seed oils and nuts. Linseeds (also called flaxseeds) and their oil typically contain 45–55 % of fatty acids as α-linolenic acid. Soybean oil, rape-seed oil and walnuts contain 5–10 % of fatty acids as α-linolenic acid. In contrast, corn oil, sunflower oil and safflower oil, which are rich in linoleic acid, contain little α-linolenic acid. Typical intakes of α-linolenic acid among Western adults are between 0.5 and 2 g/day (BNF, 1999; Burdge and Calder, 2006). In most Western diets, the main PUFA is the omega-6 fatty acid linoleic acid which is typically consumed in 5–20-fold greater amounts than α-linolenic acid (BNF, 1999; Burdge and Calder, 2006).

Philip C. Calder, in Omega-3 Delivery Systems, 2021

3.1 α-Linolenic acid from plant sources

α-Linolenic acid makes a significant contribution to the fatty acids within green leafy tissues of plants, typically comprising 50% of fatty acids present. This is because α-linolenic acid is a key component of the membranes of thylakoids within chloroplasts. However, green leaves are not rich sources of fat, so they are not major dietary sources of fatty acids including α-linolenic acid. α-Linolenic acid is found in significant amounts in several seeds, seed oils, and nuts. Linseeds (also called flaxseeds) and their oil typically contain 45%–55% of fatty acids as α-linolenic acid. Soybean oil, rapeseed oil (also known as canola oil), and walnuts contain 5%–10% of fatty acids as α-linolenic acid. In contrast, corn (maize) oil, sunflower oil, and safflower oil, which are rich in linoleic acid, contain very little α-linolenic acid. Typical intakes of α-linolenic acid among adults in Western countries are between 0.5 and 2 g/day (Baker et al., 2016; British Nutrition Foundation, 1999). In most Western diets, the main PUFA is the ω-6 PUFA linoleic acid, which is typically consumed in 5–20 times greater amounts than α-linolenic acid