There are two types of EFAs, those of the omega-6 family and those of the omega-3 family. The basic omega-6 fatty acid is called linoleic acid and it contains two double bonds. It is found in virtually all foods, but especially in nuts and seeds. The basic omega-3 fatty acid is called linolenic acid and it contains three double bonds. It is found in some grains (such as wheat) and nuts (such as walnuts) as well as in eggs, organ meats and fish if these animals are raised naturally, and in green vegetables if the plants are raised organically.

Essential fatty acids have two principal roles. The first is as a constituent of the cell membrane. Each cell in the body is surrounded by a membrane composed of billions of fatty acids. About half of these fatty acids are saturated or monounsaturated to provide stability to the membrane. The other half are polyunsaturated, mostly EFAs , which provide flexibility and participate in a number of biochemical processes. The other vital role for EFAs is as a precursor for prostaglandins or local tissue hormones, which control different physiological functions including inflammation and blood clotting.

Scientists have induced EFA deficiency in animals by feeding them fully hydrogenated coconut oil as their only fat. (Full hydrogenation gets rid of all the EFAs; coconut oil is used because it is the only fat that can be fully hydrogenated and still be soft enough to eat.) The animals developed dry coats and skin and slowly declined in health, dying prematurely. (Interestingly, representatives of the vegetable oil industry blame the health problems on coconut oil, not on fatty acid deficiency!)

In a situation of fatty acid deficiency, the body tries to compensate by producing a fatty acid called Mead acid out of the monounsaturated oleic acid. It is a 20-carbon fatty acid with three double bonds named after James Mead, a lipids researcher at the University of California at Los Angeles who first identified it. An elevated level of Mead acid in the body is a marker of EFA deficiency.

According to Peat, elevated levels of Mead acid constitute proof that your body can make EFAs. However, the Mead acid acts as a “filler” fatty acid that cannot serve the functions that the original EFA are needed for. Peat claims that Mead acid has a full spectrum of protective anti-inflammatory effects; however, the body cannot convert Mead acid into the elongated fatty acids that the body needs for making the various anti-inflammatory prostaglandins.

Peat also asserts that polyunsaturated fatty acids become rancid in our bodies. This is not true; the polyunsaturated fatty acids in our cell membranes go through different stages of controlled oxidation. To say that these fatty acids become “rancid” is misleading. Of course, EFAs can become rancid through high temperature processing and it is not healthy to consume these types of fats. But the EFAs that we take in through fresh, unprocessed food are not rancid and do not become rancid in the body. In small amounts, they are essential for good health. In large amounts, they can pose health problems which is why we need to avoid all the commercial vegetable oils containing high levels of polyunsaturates.

Peat’s reasoning has led him to claim that cod liver oil causes cancer because cod liver oil contains polyunsaturated fatty acids. Actually, the main fatty acid in cod liver oil is a monounsaturated fatty acid. The two main polyunsaturated fatty acids in cod liver oil are the elongated omega-3 fatty acids called EPA and DHA, which play many vital roles in the body and actually can help protect against cancer. Furthermore, cod liver oil is our best dietary source of vitamins A and D, which also protect us against cancer.

Actually, Peat’s argument that polyunsaturated fatty acids become harmful in the body and hence cause cancer simply does not make sense. It is impossible to avoid polyunsaturated fatty acids because they are in all foods.

EFAs are, however, harmful in large amounts and the many research papers cited by Peat showing immune problems, increased cancer and premature aging from feeding of polyunsaturates simply corroborate this fact. But Peat has taken studies indicating that large amounts of EFAs are bad for us (a now well-established fact) and used them to argue that we don’t need any at all.

Finally, it should be stressed that certain components of the diet actually reduce (but do not eliminate) our requirements for EFAs. The main one is saturated fatty acids which help us conserve EFAs and put them in the tissues where they belong. Some studies indicate that vitamin B6 can ameliorate the problems caused by EFA deficiency, possibly by helping us use them more efficiently.