Fig. 3.1 Eicosanoid formation from fatty acids.
THE EICOSANOID POWER
"Power tends to corrupt and absolute power corrupts absolutely."Lord Action, letter to MandellCreighton, April 5, 1887
Dietary fat, besides providing energy to the body, controls several vital functions such as circulation, immune system and flexibility of body membranes and cells by converting to hormone-like chemicals in the body called EICOSANOIDS. The eicosanoids are highly potent chemicals produced only in minute quantities by the body cells whenever and wherever they are needed; they cannot be stored in the body. Eicosanoids are composed of about a dozencompounds whose importance has been discovered only in the last 10 to 15 years. According to Dr. William E. Lands, the famous University of Illinois biochemist, whose book, "Fish and Human Health," has just been published by Academic Press, "Eicosanoids are how the cells chatter back and forth with each other." Many eicosanoids have opposing effects and by creating different quantities of these eicosanoids, the body maintains a wonderful balance in its various functions. Many diseases such as heart attack, stroke, cancer, migraine, arthritis, hypertension are now attributed to an imbalance in the production of eicosanoids.
Eicosanoids are mainly formed in the body by arachidonic acid (AA), an omega-6 fatty acid found in vegetable oils. Other omega-6 and some omega-3 fatty acids first convert to AA and thus indirectly contribute to production of eicosanoids. Eicosanoids are also synthesized by omega-3 fatty acids found in fish. However, eicosanoids synthesized from omega-3 acids are distinct from eicosanoids synthesized from omega-6 fatty acids. And it is this difference in the activity of the two types of eicosanoids that makes fish so good for our health.
The effects of eicosanoids range from regulation of blood pressure to causing abortion as listed in Table 3.1.
TABLE 3.1
GENERAL EFFECTS OF EICOSANOIDS
. adrenal gland function
. insulin release
. movement of calcium from bones
. blood clotting
. blood pressure
. action of drugs used in arthritis, high blood pressure and water retention in body
. food digestion
. immune system: resistance to diseases, cancer, infections
. uterine contractions: pregnancy/delivery/abortion
Eicosanoids are divided into two families: the prostaglandins (PGs), which are made by an enzyme called cyclooxygenase; and the leukotrienes, which are made by an enzyme called lipooxygenase (Fig. 3.1). Both families stimulate inflammation and contraction of muscles. Some drugs act by blocking cyclooxygenase enzyme so that PGs are not formed. For example, aspirin is recommended to reduce risk of heart disease because of its blocking of PG formation.
Fig. 3.1 Eicosanoid formation from fatty acids.
Fig. 3.1 Eicosanoid formation from fatty acids.
HARNESSING EICOSANOID POWER
The body cells can synthesize 10,000 times more eicosanoids than they normally need; so, the body has tremendous power to control its functions but this power also corrupts. Any outside influence such as diet, tension, smoke, etc., can cause the body to "explode" with eicosanoids, resulting in many diseases. Many techniques can be used to keep the eicosanoid factory operating at a low efficiency level to avert the risk of disease. These techniques are based on either reducing conversion of AA to PGs by blocking the cyclooxygenase enzyme or by reducing supply of AA, an omega-6 fatty acid in the diet.
BENEFITS AND DANGERS OF VEGETABLE OILS
Since all types omega-6 acids convert to AA and thereby contribute to synthesis of eicosanoids, any dietary source of omega-6 acids will aggravate this condition. Unfortunately, it is almost impossible to eliminate omega-6 acids since they are contained in just about all type of foods. However, cutting down on omega-6-rich cooking oils is certainly beneficial.
The most logical approach is to increase consumption of omega-3 fatty acids, derived from both vegetable and fish, replacing omega-6 acids. Unfortunately, very few vegetable sources are rich in omega-3 acids. The best vegetable sources of omega-3 acids are linseed, rapseed and soybean oils. However, the type of omega-3 acids in vegetable oils is different from those found in fish or other marine sources. The vegetable omega-3 acids are much less beneficial to health than the omega-3 acids derived from fish.
FISH COUNTERACTS THE EFFECTS OF VEGETABLE OILS
The theory which describes how fish proves beneficial to the body is called the "2:3" theory. The body produces two types of prostaglandins (PGs), a group of eicosanoids (Appendix A-5): the series-2 and the series-3 PGs. Vegetable oils, rich in omega-6 fatty acids produce more of series-2 PGs, whereas omega-3 fatty acids found in fish produce the series-3 PGs. Higher concentration of series-2 PGs is associated with heart disease, hypertension and stroke. The series-3 PGs, when present in higher concentration, block the harmful effects of series-2 PGs.
The series-2 and series-3 PGs differ in their chemical structure only minutely; the series-3 compounds have an additional pair of hydrogens missing. The fish fatty acids such as EPA produce only the series-3 PGs and, if present in large quantities, tip the balance of PGs to series-3 type in the blood.
Therefore, one of the most relevant element of blood chemistry is the ratio of omega-3 to omega-6 fatty acid. This ratio is several hundred times higher in the Eskimos than in the Western population explaining the resistance of the Eskimos to many diseases so common to the West.
Another beneficial effect of omega-3 acids is related increased concentration of leukotrienes in the body. High concentration of omega-3 acids in the blood blocks conversion of omega-6 acids to PGs and forces them to convert to leukotrienes, which improves the immune system of body resulting in increased resistance to infections and cancer.
Now that we have seen that unsaturated fat, so highly touted for its beneficial effects, is, in fact, no better than saturated fat, we will examine, in the following chapters, in further detail, how fish counteracts the effects of both.