What Omega-3 Fatty Acids Consist Of
Omega-3 fatty acids consist of three main types: alpha-linolenic acid (ALA, 18 carbons) from plant sources, and eicosapentaenoic acid (EPA, 20 carbons) and docosahexaenoic acid (DHA, 22 carbons) from marine sources, with EPA and DHA being far more potent for cardiovascular and neurological health. 1
Chemical Structure and Classification
Omega-3 fatty acids are polyunsaturated fatty acids containing 18-22 carbons with a characteristic double bond at the third position from the methyl (omega) end of the molecule. 2 These are essential fatty acids that cannot be synthesized by the human body and must be obtained through diet. 2, 3
The Three Main Types
Alpha-Linolenic Acid (ALA, 18:3n-3): An 18-carbon omega-3 fatty acid derived exclusively from plant sources including flaxseed, walnut, soybean, and canola oils. 1
Eicosapentaenoic Acid (EPA, 20:5n-3): A 20-carbon omega-3 fatty acid found primarily in fish and fish oils, serving as a precursor to specialized proresolving lipid mediators (resolvins) that actively resolve chronic inflammation. 1
Docosahexaenoic Acid (DHA, 22:6n-3): A 22-carbon omega-3 fatty acid from marine sources that comprises approximately 25% of total fatty acids in the human cerebral cortex and 50% of all polyunsaturated fatty acids in the central nervous system. 1
Critical Distinction in Potency
EPA and DHA from marine sources are substantially more potent than plant-derived ALA for cardiovascular and neurological protection. 1, 4 Human beings convert ALA to EPA to only a small extent (4-8%), and even less is converted to DHA. 1, 3 This limited conversion means that direct intake of EPA and DHA is optimal for achieving therapeutic effects. 2, 3
Dietary Sources
Marine Sources (EPA and DHA)
- Fish and fish oils provide concentrated sources of EPA and DHA, with fatty fish being the primary dietary source. 1, 5
- Fish oils are the only concentrated natural source of EPA and DHA. 3
- Other marine sources include krill oil, seal oil, and microalgae. 5
Plant Sources (ALA)
- Flaxseed oil, canola oil, walnut oil, and soybean oil contain ALA. 1
- ALA is the only source of omega-3 fatty acids available to strict vegetarians. 3
- Plant sources do not provide EPA or DHA directly. 3
Biological Functions and Mechanisms
Membrane incorporation: EPA and DHA integrate into cell membranes, affecting membrane fluidity and cellular signaling. 2
Specialized proresolving lipid mediators: EPA and DHA serve as precursors to resolvins and maresins, which actively resolve chronic inflammation and may mediate plaque regression. 1
Triglyceride reduction: Omega-3 fatty acids reduce hepatic lipogenesis and VLDL production while increasing triglyceride-rich lipoprotein lipolysis. 1
Gene transcription: These fatty acids influence gene expression related to lipid metabolism and inflammation. 2
Important Clinical Caveat
Food composition data or product claims mentioning "total omega-3 fatty acid content" must clarify the individual omega-3 fatty acids present, as ALA and EPA are not biologically equivalent. 3 This distinction is critical because the cardiovascular and neurological benefits demonstrated in clinical trials are primarily from EPA and DHA, not ALA. 1, 4