The Omega-6 : Omega-3 Balance

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Connected to · 1

cofactor · 1

Fats & Omega-3
Plant alpha-linolenic acid (ALA) has to pass through the enzyme delta-6 desaturase to be lengthened into EPA and DHA, and the omega-6 linoleic acid in the diet queues for the same enzyme. Adults convert only about 5–10% of ALA to EPA and often less than 1% to DHA, so the practical source of the long-chain EPA and DHA the body needs is fish or algae oil; flaxseed cannot stand in.
Mechanism · 3
Mechanism · Two fatty acids, one enzyme
Once inside a liver cell, ALA and linoleic acid queue for the same enzyme, delta-6 desaturase, and whichever is more plentiful takes more of it. Estimates from US food-supply data put the ratio of linoleic acid to ALA at about 6.4 in 1909 and about 10 in 1999 (Blasbalg 2011); by the mechanism, this rate-limiting enzyme is mostly occupied by linoleic acid, and ALA conversion gets crowded out. The long-chain EPA and DHA stall at this step: not because the body cannot convert, but because the workstation is taken. Both pathways share the same chain of enzymes, delta-6 desaturase, elongase and delta-5 desaturase, so they are competing for one set of equipment rather than working in parallel.
Numbers · How much ALA gets converted
Even when the enzyme is free, the pathway itself is narrow. Burdge and Calder 2005 pooled human tracer studies: dietary ALA converts to EPA at about 5–10% and to DHA often at less than 1%, and a considerable share of ALA is simply burned for energy. So eating more flaxseed does not raise long-chain omega-3 in the body in proportion. Burdge 2006 puts it plainly: the conversion of dietary ALA is limited.
In practice · Getting around the conversion
The way around the whole conversion pathway is to eat EPA and DHA directly: fatty fish twice a week, or algae oil if you do not eat fish. When EFSA assessed dietary fats in 2010, it explicitly declined to set an omega-6 to omega-3 ratio and instead gave separate adequate intakes: linoleic acid at 4% of energy, ALA at 0.5%, and 250 mg of EPA plus DHA a day for adults. Get enough long-chain omega-3 and the ratio falls on its own; pushing omega-6 down to zero is unnecessary, and no human evidence shows it helps. Flaxseed can still supply ALA; it just cannot stand in for fish.

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Two essential fats

EVIDENCEGUIDE 2

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Omega-6 and omega-3 fats are two families the human body cannot make and has to get from food, which is why they are called essential fatty acids.

The bottleneck is two enzymes. Humans lack delta-12 desaturase and delta-15 desaturase, enzymes that add double bonds to a fatty acid's carbon chain, so we cannot place a double bond at the sixth or the third carbon from the chain's far end (the methyl end). That is exactly what the names omega-6 and omega-3 describe: whether the first double bond sits at carbon 6 or at carbon 3 counted from that end. Both families are polyunsaturated fatty acids (), fats with two or more double bonds in the chain.

So how much of either raw material your body has depends on which oils you use and whether you eat nuts and fish. And the two families do not run on separate tracks inside you; they compete for the same set of enzymes that process them.

Educational content, not medical advice — consult a clinician.

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