Linoleic acid (LA)

Linoleic acid is an essential omega-6 fat, which means the body cannot make it and a small amount is genuinely required. The requirement is low, in the region of a few grams a day, and it is met easily by whole foods.

The complication is quantity. Linoleic acid is the dominant fat in soybean, corn, sunflower, safflower and similar oils, which now appear in most packaged food. Intake in Western populations is several times what it was a century ago.

It matters because linoleic acid and the omega-3 fats compete for the same desaturase and elongase enzymes. A large linoleic intake reduces how much EPA and DHA the body can make from plant precursors, and shifts the balance of the signalling molecules made downstream toward the inflammatory side.

Below 500 umol/L is under the reference range, though genuine linoleic acid deficiency is rare in anyone eating a normal diet.

Where a low result does appear, the usual context is very low total fat intake, fat malabsorption, or a diet built almost entirely around saturated and monounsaturated fats with little variety.

Because the requirement is small and whole foods such as nuts, seeds and eggs supply it, correcting a low result rarely calls for seed oils specifically.

Between 500 and 2000 umol/L your linoleic acid sits inside the reference range for this panel.

The more informative question is how this number relates to your EPA and DHA. Linoleic acid inside the range alongside low omega-3 still leaves the ratio between them unfavourable, and the ratio is what drives the downstream signalling.

Above 2000 umol/L means linoleic acid is above the reference range, which on a Western diet is a common finding rather than an unusual one.

Sustained excess suppresses conversion of plant omega-3 precursors and shifts eicosanoid production toward the pro-inflammatory side. The practical consequence is inflammatory tone that persists without an obvious cause.

Bringing it down is a matter of cooking fat and packaged food rather than of any single item. It falls slowly, over months, as tissue composition turns over.

This is the marker where the Western diet is most visible in a single number. Seed oils moved from negligible to dominant in the food supply within a few generations, and linoleic acid intake followed.

The effect is not simply that linoleic acid is high. It is that the ratio between it and the omega-3 fats moved a long way, and the ratio is what determines which signalling molecules get made.

Remove soybean, corn, canola, sunflower and safflower oils from cooking. Use extra-virgin olive oil, butter or ghee instead.

Read labels on packaged food. Seed oils appear in most processed products, including many that do not present as fatty, so the largest share of intake is usually invisible.

Avoid fried restaurant food, where the frying medium is almost always a high-linoleic oil that has been heated repeatedly.

There is no supplement for lowering linoleic acid. It comes down when intake comes down, and the change takes months as tissue turns over.

Omega-3 fish oil at 2 to 3 g combined EPA and DHA daily improves the ratio from the other side while intake falls.

GLA from evening primrose or borage oil at 300 to 500 mg is sometimes used to redirect omega-6 metabolism, though it suits some people and not others.