PG in the following is for prostaglandins. PG3s are good guys. See HDL Diet --Jerry 13-May-2001
From: 'Fats that Heal Fats that Kill' by Udo Erasmus, p261.

The rate at which the average human body can convert LNA to EPA has been measured in one study using normal adults to be 2.7% per day of the LNA administered - nutritional intake of co-factors necessary for conversion and PG production was not measured.

Since 80% of the population gets less than recommended amounts of al least one of the co-factors, optimum quantities of essential nutrients, especially vitamins B3, B6, and C, magnesium, and zinc might even boost the conversion of LNA to EPA and its conversion into PG3s above 2.7% per day.

A persons fat deposits should contain 2% LNA (2.4% is normal in bodies built from traditional diets). This amounts to 200 grams of LNA available for conversion in a normal persons 10 kg of body fat. Using the 2.7% figure, the body can make 5400 mg of EPA, as much as one would get from about 18 large (1000-mg) capsules of the w3-richest fish oil. Sellers of fish oil who claim that conversion of LNA to EPA and DHA in humans is not fast enough may be protecting sales rather than telling the truth, since they recommend only 3 capsules per day.

If a person has no w3s in their body but takes 2 tablespoons of flax oil each day, of which 50% is LNA, their body can make 378 mg of EPA, which is what two large capsules of fish oil will supply. In w3 supplementation after long-term deficit, 3 to 5 tablespoons are often used. The LNA in this oil can be turned into as much EPA as 3 to 5 large capsules of fish oil will supply. The advantage is that the EPA made in our body is fresher, LNA-containing seeds and oils are available in fresher conditions than fish oils because they are simpler to produce (less processing). They are also more stable, and are less likely to contain toxic ingredients like polychlorinated biphenyls (PCBs).

A few people might be genetically unable to make the conversion. These people would require fish or their oils in their diet.

Dietary saturates, monounsaturates, trans- fatty acids and cholesterol all slow down conversion, and deficiencies, of vitamins B3, B6, C, magnesium, or zinc also inhibit conversion,

Most people don't get much LNA in its natural state in their diet. The richest sources of LNA come from flax, chia, and hemp seeds and their oils, which are new to the marketplace.