Key Findings:
ALA can be converted to longer-chain n-3 PUFA such as EPA (20: 5n-5) and DHA (22: 6n-3), and it is difficult to distinguish health effects of ALA from those of its longer-chain metabolites. Epidemiological studies show that ALA intake is inversely associated with risk of CVD. Intervention studies show that increased ALA intake can beneficially affect a range of cardiovascular risk factors including blood cholesterol, LDL-cholesterol and TAG concentrations, vascular reactivity, platelet aggregation and inflammation. The author recognizes that young women possess greater capacity for conversion to EPA and DHA.
Increased ALA intake may lead to greater reserves of EPA and DHA in adipose tissue which could be mobilized and supplied to the fetus during pregnancy. Increased dietary intake of ALA by young women may provide a means of ameliorating inflammatory disease symptoms.
ABSTRACT:
a-Linolenic acid (ALA; 18 : 3n-3) is essential in the human diet, probably because it is the substrate for the synthesis of longer-chain, more unsaturated n-3 fatty acids, principally EPA (20 : 5n-3) and DHA (22 : 6n-3), which confer important biophysical properties on cell membranes and so are required for tissue function. The extent to which this molecular transformation occurs in man is controversial. The present paper reviews the recent literature on the metabolism of ALA in man, including the use of dietary ALA in b-oxidation, recycling of carbon by fatty acid synthesis de novo and conversion to longer-chain PUFA. Sex differences in ALA metabolism and the possible biological consequences are discussed. Increased consumption of EPA and DHA in fish oil has a number of well-characterised beneficial effects on health. The present paper also reviews the efficacy of increased ALA consumption in increasing the concentrations of EPA and DHA in blood and cell lipid pools, and the extent to which such dietary interventions might be protective against CVD and inflammation. Although the effects on CVD risk factors and inflammatory markers are variable, where beneficial effects have been reported these are weaker than have been achieved from increasing consumption of EPA + DHA or linoleic acid. Overall, the limited capacity for conversion to longer-chain n-3 fatty acids, and the lack of efficacy in ameliorating CVD risk factors and inflammatory markers in man suggests that increased consumption of ALA may be of little benefit in altering EPA + DHA status or in improving health outcomes compared with other dietary interventions. (Authors Abstract)
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