This week I’d like to share some of the things I’ve learned about two particular polyunsaturated fatty acids, omega-3 and omega-6 fatty acids. 

Let’s start with omega-3 fatty acids. These are compounds in the form of a long chain of carbon molecules with several double bonds, each of which acts as a pivot point. Flexible pivot points confer the ability to move in many directions, essential for movement and flexibility. Omega-3s owe their flexibility to all those double bonds, the last of which is located just three carbons from the tail, or omega, end of the molecule. That’s why it’s called an omega-3 fatty acid. Omega means end. In contrast, omega-6 fatty acids contain fewer double bonds, and the last one is located six carbons from the tail. Hence, omega-6. 

Among many other essential functions, omega-3’s play a vital role in photosynthesis, whereby green leaves convert sunlight to plant food. This is why green leaves are an important source of omega-3s.

Omega-3 fatty acids are found in all green plants (another reason to eat your vegetables). The largest mass of greens on Earth is phytoplankton, tiny sea plants that are eaten by little fish, which are then eaten by bigger fish, and so on. Sea creatures eat literally tons of phytoplankton, in part because fish must take in at least one full percent of their calories as omega-3s in order to keep their blood liquid and survive in cold water environments. Warm-blooded animals, on the other hand, need only half that. This is why fish, fish oil, and algae are such good sources of omega-3s.

In biological systems, two significant omega-3 fatty acids are called DHA and EPA. EPA is a blood thinner with anti-inflammatory properties. DHA is incorporated into cell membranes to keep them flexible and functional. DHA is like a “quick-change artist” with hundreds of possible configurations. According to Susan Allport*, “DHA creates membranes with…behavior that is almost liquid-like.” Cell membranes aren’t inert like dry wall. They live and breathe, and they function to keep the cell’s internal environment completely separate from the outside environment.

DHA has other important functions. It makes up 25 percent of brain tissue. It reduces the likelihood of heart arrhythmias, or abnormal rhythms. It helps the eye to see better by increasing the amount of rhodopsin, a light-responsive protein in the retina’s rods. DHA also appears to improve insulin sensitivity, meaning that it lowers the risk of diabetes and obesity.

Omega-3s do, however, have one important limitation: All those double bonds react easily with oxygen, which makes them, chemically speaking, unstable. In fact, oxidation is the major cause of food rancidity. This reactivity makes omega-3s an unreliable way to store fat in nature.

And that is where omega-6s enter the picture.

Omega-6s, less reactive because they have fewer double bonds, are a much better choice for a different job — storage. This is why omega-6s are the main fat in grains and seeds. Where long-term storage is all-important, the stability of omega-6s makes them the preferred form in which to store fat. Plants store fat as omega-6s until seeds germinate and initiate photosynthesis. Then they release an enzyme that converts omega-6s to omega-3s. Plants are able to convert omega-6s into omega-3s whenever they need.

With the exception of lions, most animals and humans do not have this enzyme, so once an omega-6, always an omega-6. And if you eat a diet high in omega-6s, your cell membranes will not be as flexible as if you ate sufficient omega-3 fatty acids.

The stable chemical configuration of omega-6s increases shelf life considerably, which makes them the leading fatty acid of choice for ultraprocessed food products, including vegetable oils. It explains why it is not coincidental that the ratio of omega-6s to omega-3s in our diet has climbed from approximately 1:1 throughout history to upwards of 50:1 or higher today. People living on fast food and doughnuts may be eating 50 times as much omega-6s as omega-3s. That’s a problem.

Don’t think of omega-3s as good for you and omega-6s as bad. It’s not about good and bad. It’s about being in a balanced ratio. Omega-6 fatty acids in plants serve as a stable, reliable system for storing fat until the plant needs omega-3s. Omega-3s are flexible, and omega-6s are stiff. Omega-3s are reactive, whereas omega-6s are stable. We need both to function optimally.

Omega-6s, with fewer double bonds, are more stable and, therefore, less prone to oxidation and breakdown, which is why omega-6s are found in highest concentration in grains and seeds. Dry beans may remain viable for centuries under certain circumstances. That is obviously not true of lettuce, under any circumstances.

Stiff membranes may be good for seeds and grains, but they are a tremendous liability for green leaves, not to mention brains, blood vessels, eyes, and joints. High blood pressure, inflammatory diseases, and insulin resistance are predictable consequences of stiff cell membranes.

*Author of The Queen of Fats: Why Omega-3s were Removed from the Western Diet and What We Can Do to Replace Them