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Importance of Omega-3
 By Dr. Neil Nedley

Omega-3 fats are emerging as an im­portant nutritional element in brain sci­ence. There are actually two types of fat that are absolutely essential in our diets— omega-6 and omega-3 fats. The omega-6 fats are abundant in many foods, so it is extremely rare to see mental or physical problems develop due to a shortage of omega-6. Omega-3 fats are not so abun­dant, so it is more common to see adverse effects from a diet too low in omega-3.

Tryptophan tends to be low in the diet when calorie intakes are low, but omega-3 can be too low in the diet even if calorie intakes are more than adequate. Even a high fat diet can be too low in omega-3, particularly when the ratio of omega-3 to omega-6 in the diet is low. Interestingly, the ratios of these two fats in the blood do have a direct relationship to rates of depression. The lower the omega-3 to omega-6 ratio, the higher the rate of depression. Recent research demonstrates that bipolar disorder (manic-depression) in addition to major depression (unipolar disorder) can be helped by a diet high in omega-3.

           Most people increase their omega-3 fat intake by eating fish. Most fish, however, are not good sources of omega-3 fats. Cold water ocean fish are good sources, not be­cause their bodies manufacture omega-3, but because they eat a lot of cold saltwater seaweed, which is very high in omega-3 fats. It is important to note that the original sources of omega-3 fats are plant sources, and when we obtain our omega-3 from fish we are getting the nutrients second-hand. The omega-3 content of certain fish is listed in Figure 3.Note the wide variation in omega-3 content from one kind of fish to another. For example, drum fish, which has the low­est omega-3 content, has only 25 percent as much as Atlantic mackerel.

There are many benefits of a diet with adequate omega-3 fat, but there is a down­side in getting it from fish. I list six major health problems of getting omega-3 fats from fish in the book Proof PositiveFor the sake of brevity I will elaborate on only one of these concerns here.

 Fish Are Contaminated

Fish collect and concentrate toxins in their fatty tissues. These toxins include pes­ticides, chlorinated hydrocarbons, dioxin, chlordane, and mercury. As of 1996, 47 states had fish consumption advisories that warn against eating certain species. They cover 1,740 rivers and lakes (including all of the Great Lakes) and large chunks of coastal areas. The most common reason for consumption advisories is mercury, which can cause brain and nerve damage especially to fetuses and young children. Large fish like fresh tuna, swordfish, and shark contain the highest levels of mercury. Despite the popular belief that fruits and vegetables have the greatest risk of pesticide contamination, FDA research reveals that domestic fish products contain significantly more pesticide residues than domestic fruits, grains, or vegetables. Bluefish, along with lake trout and other freshwater fish caught in inland lakes, are most likely to be con­taminated with carcinogens like dioxin or PCBs (polychlorinated biphenyls)

Contaminated Fish from Con­taminated Waters

Pesticides are an extremely important issue. Worldwide, there are more than 900 different active pesticides in some 40,000 different chemical formulations. In the U.S., about 600 pesticide ingredients are used, accounting for some 800 million to 1 billion pounds per year. Huff and Haseman reviewed some 200 rodent stud­ies. They concluded that "there is consider­able evidence that exposure to certain pes­ticides may present real carcinogenic hazards to humans."

How do fish become exposed to pesti­cides? One major cause is agricultural run­off. When a farmer sprays his fields, a por­tion of the chemicals run off into neigh­boring creeks and streams, and ultimately into rivers and oceans. Overflows of sew­age, faulty septic systems, boating wastes, and poisonous run-off from city streets have also contributed to the pollution of waters. These waters are sometimes considered so dangerous that signs like the one shown in Figure 4, "Swimming Prohibited," are erected on some beaches.


 If swimming in the water is hazardous for humans, it is ironic that people still go fishing in these areas. The signs are not "crying-wolf." Illnesses such as gastroenteritis, dysentery, hepatitis, and more have resulted in swimming in contaminated water.

Cancer in Fish is Increasing

              The risk of spending time in bodies of water on our globe is highlighted by a disturbing trend among fish. Fish are found with more cancer now than 50 years ago. A Canadian biologist, Ron Sonstegard, has examined bottom-dwelling fish in the Great Lakes and the rivers that feed them. He has found tumors in every fish species—often malignant. For example, 30 percent of the bull-heads in Lake Erie had liver cancer.

            The Ph.D. nutritionist and author, Dr. Winston Craig, in commenting on these findings, added three more sobering facts: 1) the Great Lakes situation is not unique—cancerous fish turn up from Puget Sound to the Gulf of California and from the Hudson River to the Florida Keys; (2) National Cancer Institute data show an increased death rate from cancer among people living in areas where fish have ex­ceptionally large amounts of tumors; (3) the toxic nature of what is found in some of our waterways is astonishing. When sediments from the bottom of Lake Erie were painted on the skin of mice, the mice de­veloped skin cancers.  Although Craig's insights may not nec­essarily prove human risk, they surely raise serious concerns about the human health hazards related to the "epidemic" of can­cers in fish.

            Possible links to cancer from contaminated fish are summarized in Figure 5

Evidence Linking Fish contamination to Cancer

                Rather large amounts of fish die in droves every year throughout our country due to pollution. The Environmental Protection Agency (E.P.A.) of the U.S. govern­ment has attempted to trace the amount of fish kills due to pollution as well as other causes. Figure 6 reports by state the num­ber of fish kills caused by pollution in 1993.

Number of reported fish kills caused by pollution

Each fish kill in the figure can repre­sent literally thousands of fish. The E.P.A. admits that these statistics greatly underes­timate the actual number of fish kills, since 15 states did not report or keep track of their fish kills. Also, many fish kills occur that cannot be definitely proven to be due to pollution. Pesticides were the most fre­quently identified toxic pollutant causing fish kills, followed by oil and gasoline prod­ucts, chlorine, ammonia, heavy metals, and other toxic substances. Unfortunately, many ill fish that are suffering from these pollut­ants are caught by fisherman, taken to mar­ket, and consumed by humans who think they are eating healthy food.