Humans cannot convert omega-6 fatty acids into omega-3 fatty acids, even though plants can. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the two main long-chain highly unsaturated fatty acids (HUFAs) in the omega-3 series.
Another form of omega-3 is short-chained alpha linolenic acid (ALA). ALA is converted to long-chain omega-3s in a slow process that relies on many different enzymes. Unfortunately, these same enzymes also are necessary to convert short-chain omega-6s into long-chain omega-6s. This means that the more omega-6s that we consume, the less we can convert short-chain omega-3s into long-chain omega-3s. This is why it is important to eat both enough long-chain omega-3 fatty acids and to limit the amount of omega-6s ingested.
On average, only about 5% of ALA is converted to EPA, and only 0.5% of ALA is converted to DHA. However, eating foods rich in ALA to replace foods rich in omega-6s is advantageous, because the two are in competition for the same enzymes necessary to produce long-chain fatty acids.
DHA is necessary for the correct construction and functioning of membranes in the nerves and active muscle. EPA and DHA both are important for cardiovascular health, and EPA is critical in the anti-inflammatory response. Arachidonic acid (AA) is a long-chain omega-6 fatty acid. Enough AA is necessary to help defend and repair the body because of its inflammatory properties, but too much leads to a highly reactive or over-reactive inflammatory response. This in turn can lead to conditions such as coronary disease or allergies.
The average ratio of omega-6s to omega-3s is roughly 10:1 to 20:1 in developed countries. The optimal ratio is thought to be 4:1 to 5:1. The Palaeolithic hunter/gatherer diet provided a ratio closer to 1:1.
A Mayo Foundation paper, published in 2008, stated that ideal consumption of EPA and DHA are as follows:
- 1 gram (g)/day for people with known coronary artery disease
- 500 milligrams (mg)/day for people who do not have coronary artery disease
- 3-4 g/day for people with hypertriglyceridemia
Download the Omega 3 vs Omega-6 handout, to view the chart which illustrates the omega-3 and omega-6 content of various animal-based foods.