Unlike saturated and monounsaturated fatty acids which can be synthesized by all mammals, including humans, the omega-3 PUFA cannot be easily synthesized in the body and must be provided through the diet.
The unique feature of marine oils, such as seal oil, relates to their high content of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and, to a lesser extent, docosapentaenoic acid (DPA). These PUFA are formed in unicellular phytoplankton and multicellular sea algae and eventually pass through the food web and become incorporated into the body of fish and higher marine species. The high content of omega-3 fatty acids in marine lipids is suggested to be a consequence of cold temperature adaptation in which omega-3 PUFA remain liquid and oppose any tendency to crystallize.
OMEGA-3 ESSENTIAL FATTY ACIDS
Health experts have concluded that a large percentage of the population have a diet which is deficient in long chain, highly unsaturated essential fatty acids. For example, it is estimated that 80% of all Americans have a deficiency. As many as 60 medical conditions are linked to this deficiency or have been identified as benefiting from Omega-3 supplementation.
The three most important of the long chain fatty acids are eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and docosapentaenoic (DPA). These fatty acids are deemed "essential" because they have a vital role in maintaining the integrity and fluidity of the membrane which surrounds human cells and because they cannot be synthesized by the body. Without a healthy membrane, the ability of cells to hold water, nutrients and electrolytes is impaired. As a consequence, the membrane may no longer protect the cell from damage caused by free radicals which are the products of oxidation within the body.
They also lose their receptivity to hormones and their ability to relay chemically encoded instructions for cellular repair. The search by health conscious consumers for foods containing omega-3 fatty acids can be a frustrating one. Given the trend toward mass production and packaging of meals and meal ingredients, consumers have less knowledge of, or influence over the contents of their food. The move by some manufacturers toward mono or polyunsaturated fats as substitutes for saturated fats is a positive step. Generally however, the polyunsaturates most often selected are those derived from vegetable oils which contain significant amounts of omega 6 but little or no omega-3. While omega 6 and omega-3 fatty acids are both necessary to good health, most health experts agree that, they should be consumed in a balance of 4:1 respectively. Today's Western diet has created a serious imbalance with current consumption on average of 20 times more omega 6 than omega-3. Concerned consumers have begun to look for health food supplements to restore the equilibrium. Three major sources of omega-3 supplements are flaxseed oil, fish oils, and seal oil.
The past decade has seen rapid growth in the production of flaxseed and fish oils. Both types of oil are considered to be good dietary sources of polyunsaturated fats but are less effective than seal oil in supplying omega-3 fatty acids. Flaxseed oil contains no EPA, DHA or DPA but rather contains alpha-linolenic acid--a precursor to EPA. There is evidence however that the rate of metabolic conversion can be slow and unreliable. Some research has shown that supplementation with flaxseed oil may result in higher tissue levels of alpha-linolenic acid without any corresponding increase in EPA. Fish oils vary considerably in the type and level of fatty acid composition depending on the particular species and their diets. For example, fish raised by aquaculture tend to have a lower level of omega-3 fatty acids than those in the wild. some research has shown that seal oil is more beneficial to those at risk of heart disease and diabetes than is fish oil.
The relative absence of DPA in fish oil and the slower rate at which the body assimilates EPA and DHA from fish oils have been cited as factors. The most direct and complete source of omega-3 oils is found in the blubber of certain marine mammals, especially the harp seal. Among its advantages is that the body's absorption of omega-3 from seal blubber is faster and more thorough than is the case with flaxseed and fish oils. This is due, in part, to the molecular configurations of the EPA and DHA in seal oil which varies slightly from that found in fish oils. The essential fatty acids found in seal oil include a high level of DPA (up to ten times that of fish oils). There is growing evidence that DPA is the most important of the essential fatty acids in keeping artery walls soft and plaque free. A further advantage of seal oil is that it is more stable than fish oil and less vulnerable to the natural process of oxidation. However, there are challenges in producing a satisfactory grade seal oil for administration as a dietary supplement to humans. Seal oils, like other health food oils, are susceptible the natural process of oxidation. The primary and secondary products of oxidation may give rise to unacceptable flavours and odours in the oil, impair digestibility of the oil, and produce fee radicals which can damage or destroy the body's cells. The causes of oxidation include exposure to air, heat, light ("harmful light" refers to light in the range of about 4,250 5,100 angstrom), oxygen and certain metals such as iron. Oxidation of polyunsaturated oils limit their shelf life. As fish and seal oils become oxidized their taste and odour may become objectionalble. For example, one study of encapsulated fish and plant oil samples found that many commercially prepared oils had poor oxidative stability (VKS Shuklia, EG Perkins, "Rancidity in encapsulated health-food oils", Inform, vol. 9, no. 10 (October 1998). Clearly there is a need for nutritional oils that offer higher levels of oxidative stability. Health Canada recommends that the daily diet contain at least 1.8 grams of omega-3 fatty acids.
The U.S. Department of Health and Nutrition Services has also acknowledged that health benefits would accrue to the general population if dietary intakes of omega-3 polyunsaturated fatty acids (PUFA) were increased. At present, the average consumption of omega-3 PUFA in North America and Europe is less than one gram per day. The administration of seal oil as a dietary supplement could fill this gap if a suitable refined oil could be produced.