Written by Chris Masterjohn Phd
September 22 2010 15:02
The Perils of PUFA: Oxidative StressIn 1985, the lipid researcher Hugh Sinclair gave a pre-banquet speech on his seventy-fifth birthday before the Second International Congress on Essential Fatty Acids, Prostaglandins and Leukotrienes in London, in which he described the deleterious effects of one hundred days on an “Eskimo diet” of seal blubber and undeodorized mackerel oil. He went on the diet to measure his bleeding time because the weather during a recent trip with several colleagues to northwestern Greenland had curtailed him from measuring the bleeding times of real Eskimos. Despite a daily supplement of vitamin E, his blood and urine levels of malondialdehyde (MDA)—a product of the oxidative destruction of PUFA (see Figure 3d)—rose to fifty times the normal level. Although MDA causes birth defects, Sinclair was not worried about having “misshapen offspring” because his sperm had disappeared.31
Sinclair’s experience illustrates one of the unique dangers of all essential fatty acids, regardless of their class—their vulnerability to oxidative stress.
Figure 3. Oxidative Stress and the Shattering of Delicate PUFAs
Compounds with unpaired electrons, called free radicals, are capable of
stealing electrons from, or “oxidizing,” PUFAs. PUFAs are uniquely vulnerable
to oxidation because they are the only fatty acids with two or more double
bonds, and it is the carbon that lies directly between two double bonds that
is vulnerable to oxidation at physiological temperatures. In the figure, a lipid
peroxyl radical (LOO) steals an electron and a hydrogen atom from a PUFA.
b. Having stolen the electron and hydrogen atom, the lipid peroxyl radical becomes
a lipid peroxide (LOOH). The addition of oxygen to the oxidized fatty
acid forms a new lipid peroxyl radical that can oxidize another PUFA (LH).
c. There are now two lipid peroxides, one shown in its chemical structure and
one abbreviated as LOOH. The newly oxidized fatty acid (L•) can now continue
the chain reaction.
d. Many of these oxidized fatty acids will continue to degenerate into smaller
compounds, like a glass that shatters into many pieces. One such compound,
malondialdehyde (MDA), is shown in the figure. MDA is particularly dangerous
because it can leave the membrane and damage proteins, DNA, and
other important cellular structures. This process can be likened to the shattering
of delicate glass, which results in a mess of dangerous shards that must be
properly cleaned up.
Oxidative stress, or lipid peroxidation, shown in Figure 3, can be thought of as the destruction of structurally and functionally important molecules within the body, beginning with the shattering of PUFAs. PUFAs, in this sense, are like delicate glass. Glass performs many useful functions: we use it to protect ourselves and our property from the assaults of raging storms, for the utensils from which we eat and drink, to see when our vision fails, to examine complex specimens whose details we cannot otherwise distinguish with the naked eye, and in many other more sophisticated examples of modern technology. At the same time, glass is delicate and can shatter. When glass shatters, it invariably leaves behind a mess of dangerous shards. Anyone who breaks a glass on their kitchen floor knows to clean up the shards immediately, lest they or their family cut their feet by walking on them. Likewise, when PUFAs shatter they leave behind shards such as MDA, which are capable of damaging proteins, DNA and other structurally and functionally important components of our cells.
The best way to avoid shattering glass is to be careful with how one uses, cleans and stores it. Nevertheless, the danger of breaking glass will increase simply by having too much of it around. Likewise, the consumption of excess PUFAs increases oxidative stress even when the oils are fresh and properly cared for. Consumption of fresh, non-oxidized DHA, EPA or omega-3-rich perilla oil increases markers of oxidative stress in rats.58 Rats fed 30 percent of their diet as corn oil have double the rate of lipid peroxidation, half the aerobic capacity, and 42 percent lower glycogen stores in their heart tissue compared to rats fed an equal amount of coconut oil.59 A randomized, doubleblind, placebo-controlled trial likewise showed that six grams per day of fish oil increased lipid peroxides and MDA in healthy men, regardless of whether they were supplemented with 900 IU of vitamin E (see Figure 4).60
Sinclair might have better replicated the “Eskimo diet” had he sought the guidance of an Eskimo. Arachidonic acid is necessary for sperm production, and the liberal consumption of glands and other organs rich in arachidonic acid may protect the Inuit and Aleut peoples from the high levels of EPA they obtain from fatty fish and marine oils.31 There may be other components of their traditional diets that limit the vulnerability of PUFAs to oxidative stress, such as antioxidants like coenzyme Q10, lipoic acid, and preformed vitamin A found abundantly in organ meats, or other unknown factors. Human studies have generally used alpha-tocopherol, a form of vitamin E, to protect against the oxidation of fish oils within the body, but supplements of pure alpha-tocopherol suppress levels of gamma-tocopherol, a different form of vitamin E with a unique spectrum of antioxidant protection. Some of the main oxidants in human blood, moreover, are water-soluble so PUFAs require water-soluble antioxidants such as vitamin C for protection. Exactly which components of the traditional Inuit diet best protected them from their high intake of fish oils is unclear, but Sinclair’s experience demonstrates the danger of attempting to replicate a particular peculiarity of one group’s traditional diet without replicating the diet as a whole.
Figure 4. Fish Oil Increased in Lipid Peroxides and MDA in Humans While Vitamin E Had No Effect
A double-blind, randomized, placebocontrolled trial compared six weeks of supplementation with six grams per day of omega-3 fatty acids from menhaden fish oil to supplementation with six grams per day of olive oil, with or without 900 IU per day of vitamin E as synthetic alpha-tocopherol, in healthy men. For each group, the bar on the left represents the change in lipid peroxides, and the bar on the right represents the change in MDA. Asterisks indicate a statistically significant increase over the course of the six weeks. Fish oil supplementation caused a significant increase in lipid peroxides while MDA and vitamin E had no effect. Adapted from the data in reference 60.