Polyunsaturated fatty acid (PUFA) is the technical term for a type of fat (fatty acid) with two or more (poly) double bonds (unsaturated). They exist in many different forms, varying in chain length, degree of unsaturation, and rotation around the double bonds. The pharmacology and biochemistry of their actions are complex, yet their detrimental effects on human health are very clear and well established.
Sources of PUFAsPUFAs are found in all natural foods in varying amounts, but fatty foods contain the most. In general, vegetable oils are the most concentrated sources of PUFAs in the American diet and include sunflower oil, safflower oil, corn oil, flax oil, sesame seed oil, pumpkin seed oil and canola (or rapeseed) oil. The exceptions include plants that grow in tropical climates, such as the oils extracted from chocolate and coconuts. These oils are highly saturated, and so are very stable and undoubtedly safe and beneficial.
Mechanisms of PUFA-induced damagePUFAs undergo oxidation in the body in reactions that are both controlled and uncontrolled. The products of controlled oxidation are known as eicosanoids. These hormone-like products have a wide range of damaging effects in very small amounts and are involved in various diseases. Aspirin curtails the production of these eicosanoids and is the mechanism by which it prevents inflammation, pain, fever and some cancers.
PUFAs also undergo random oxidation (also referred to as peroxidation or auto-oxidation) rapidly under the conditions of the human body and are a source of tissue-damaging free radicals. These products of peroxidation promote inflammation and their deleterious effects may be the cause of aging, atherosclerosis and cancer. Alpha-tocopherol (Vitamin E) stops the chain of peroxidation.
In the absence of PUFAs in the diet, the body synthesizes an omega-9 fatty acid called Mead acid (5,8,11-eicosatrienoic acid). This relatively stable fatty acid displaces the PUFAs in the tissues and curtails the formation of inflammation promoting leukotrienes. In general, the more double bonds or degree of unsaturation, the more potentially damaging the molecule is.
When large amounts of PUFAs are consumed, they are stored and between meals, they are released. In free form, they poison the mitochondria (where oxidative metabolism occurs), impair communication within the cell, impair the action of enzymes that dissolve blood clots and digest dietary protein, and inhibit the thyroid. Inhibiting the thyroid slows the metabolism and diminishes the ability to metabolize the PUFAs, accelerating their toxic effects. Stress, low blood sugar, and high intensity exercise increase the lipolytic enzymes. Niacinamide (vitamin B3) restrains them.
Practical suggestions:
It is impossible to completely avoid PUFAs if one eats a natural diet and so the ongoing discussion of whether or not some PUFAs are essential is moot. Even "fat-free" foods contain trace amounts of PUFAs. A rational approach would be to avoid the PUFA-containing foods to the extent that is possible and redirect the choice of fats to the ones containing the most saturation. One study showed that just 0.5 percent of the diet in PUFAs is enough to trigger cancer. The best choices include fats from ruminant animals (i.e. cows, sheeps and goats), coconut oil, cocoa butter and palm kernel oil. Olive oil is generally safe, but contains 10 percent PUFAs so should be used in moderation.
