With all of these things seeming to favor the use of fish, how do we explain the perplexing illustration at the opening of this chapter? The authors of Jane's story knew the explanation and stated it clearly: "...compared with a diet that is essentially vegetarian, the consumption of fish will increase dietary cholesterol and often the intake of saturated fatty acid as well. The net result may be, as in this patient, a rise in LDL levels."5 Other more recent studies have confirmed that fish oil consumption will very likely increase the LDL cholesterol in most people.6,7 As explained in Chapter 3 on heart disease, LDL is the "bad" cholesterol that can produce clogged arteries throughout the body.
Let us look at the two points made in this distinguished publication and see why fish presents a problem. First, fish is an animal product, and it therefore contains cholesterol. In fact, there is not much difference between the cholesterol content of fish and other animal products such as chicken, turkey, or even pork and beef. These cholesterol levels are also tabulated in Figure 14: Cholesterol in Foods in Chapter 3 on heart disease.
The fact that fish contains cholesterol puts it in a completely different class than all plant products. You will recall that all plant sources of nutrition have absolutely zero cholesterol. A comparison of the cholesterol content of various fish and fish oils is found in Figure 1: Cholesterol Content of Various Fish Oils and Beef.8
Notice that the cholesterol levels are stated for the amount of 15 grams of fish oil, which is a standard supplementation dosage for cardiovascular disease.9 We see that these amounts of cholesterol in fish oil are equal to or greater than the cholesterol in a generous serving of T bone steak, as shown in the bar on the left side of Figure 1. It is no wonder that fish oil can raise the serum cholesterol. The American Heart Association is known for being soft on dietary guidelines; nevertheless, even their most liberal diet for heart disease still forbids more than 300 mg of cholesterol per day. Supplemental use of fish oil can go a long way to exceeding even this recommendation.
The second point raised by the authors of Jane's story has to do with the issue of saturated fat. Compared to other meats, fish has a favorable polyunsaturated to saturated fat ratio (P/S ratio). However, it does not have as favorable a ratio as most plant-derived foods. Again, while it is true that those who have been eating red meat can bring their cholesterol down somewhat by switching to a fish-based diet, a vegetarian diet is much more effective. The point is that fish raises blood cholesterol levels less than red meat or even poultry. Compared to plant products, however, fish raises cholesterol levels.
Although many lay people have been drawn to fish because of its advertised cholesterol-lowering effects, it is interesting to revisit the Holland study that helped to stir up so much interest.10 When the authors published their data showing a 50 percent drop in heart disease deaths, they included an important fact that has been often overlooked: the fish eaters and heavy red meat eaters had virtually identical cholesterol levels. The fact that fish may not lower cholesterol begs a question: what is there about fish that might reduce heart disease risk even though cholesterol levels may not be altered? The answer may lie with another compound, called omega-3 fats.
Omega-3 Fatty Acids Reduce Heart Disease Risk
Certain fish are rich sources of omega-3 fatty acids. Such fish include salmon, sardines, mackerel, and some other fatty fish.11 The omega-3 fats in these fish are long-chain polyunsaturated fatty acids which include eicosapentaenoic acid (EPA), a fat with some unique heart advantages. For example, EPA helps to decrease the stickiness of platelets, the body's clotting cells.12 This is important: anything that helps to prevent platelets clumping together decreases their tendency to plug up blood vessels. This in turn can help to decrease the risk of a blood clot forming in a heart blood vessel and causing a heart attack.
Omega-3 fat can also help to mildly decrease blood pressure.13 Many experience an actual decrease in the serum triglycerides from consuming this class of fats.14 For these reasons and others, it is likely that these omega-3 fats at least have some tendency to decrease the rate of atherosclerosis.15 Beyond these reasons, animal models suggest that if a heart attack does occur, omega-3 fatty acids may decrease the amount of muscular damage occurring from the attack.16 These unique fats also appear to decrease the likelihood of blood vessels blocking up again after angioplasty ("the balloon procedure" used to open up blocked heart arteries),17 and can also decrease the rate of clogged bypass grafts following bypass surgery.18 A summary of these omega-3 benefits is shown in Figure 2: Omega-3 Fats Fight Heart Disease.
Considering the evidence, should we eat fish to help decrease heart disease risk? A further look at other population studies may help to provide the answer. We have already looked at the Dutch study that demonstrated a 50 percent decrease in coronary artery disease deaths among daily fish eaters.19 While a 50 percent reduction is significant, a much greater reduction occurs among total vegetarians. A study of Seventh-day Adventist men on a total vegetarian diet showed that their risk was lowered by 86 percent.20 The results in both studies are not unexpected: those on a poor diet may benefit from adding fish in place of other more harmful foods. Adding fish may lower their heart disease risk; it might even lower their cholesterol levels. However, they cannot get the magnitude of benefit that the optimal diet provides. As we have seen in the two previous chapters, many lines of evidence demonstrate that the optimal diet for heart disease prevention is the total vegetarian diet.
Another population study is of particular note. This published report from Harvard University represents probably the most statistically powerful research ever conducted to examine the fish-heart relationship. Where the Dutch study looked at only 852 men, the Harvard researchers studied a phenomenal 44,895 male health professionals.21 The researchers' findings were astonishing: men who ate fish several times a week were just as likely to have heart disease as those who ate it only once a month. If anything, there was a suggestion that the men who consumed six or more servings of fish per week had a somewhat greater risk of coronary heart disease than those who consumed one serving per month or less. The explanation most likely has to do with what foods other than fish were included in the diet. The better the diet, the less benefit derived from adding fish. On an excellent diet, fish will increase rather than decrease heart disease risk. Smoking Negates Benefits of a High-fish Diet
Intake of omega-3 fatty acids in a high-fish diet by those who smoke does not protect against coronary death. In fact, it might have the opposite effect. A six year study spearheaded by Dr. Pirjo Pietinen of Helsinki, Finland, involved 22,000 middle-age smoking men for cardiovascular disease risk and intake of fatty acids. Those who had the highest intake (eating more fish) had a 30 percent increased risk of dying of coronary disease compared to those who had the lowest intake.22
In summary, regarding the heart, there is strong evidence that fish only worsens an excellent diet and that in smokers a high fish diet is also detrimental. However, could there be other benefits beyond heart disease from eating fish and their accompanying omega-3 fatty acids? Should we eat at least some fish to reap those benefits? Let us look at further information on omega-3.
Other Omega-3 Benefits
The advantages of a diet high in omega-3 do not stop with the heart. The various known non-cardiac benefits of following a diet high in omega-3 fatty acids are listed in Figure 3: Disorders that may Benefit from Omega-3 Fatty Acids.23 Omega-3 fatty acids are of benefit to those with rheumatoid arthritis and other inflammatory arthritic conditions.24, 25, 26, 27 Rheumatoid arthritis is a crippling type of arthritis. Often the hands and other joints become seriously deformed. In addition, it tends to affect the whole body and not just the joints. It can affect blood vessels, the spleen, heart, lungs, and skin.28 Furthermore, this disease can be notoriously difficult to treat. Often the drugs employed have serious side effects. Thus, when the news came out that a dietary change could help this devastating disease, thousands of sufferers no doubt rejoiced.
The omega-3 fats are also helpful in psoriasis.29, 30 Psoriasis is a skin condition that can range from mild itchiness and scaling to disfiguring and painful rashes that may ooze and bleed. Omega-3 fats along with other polyunsaturated fats can also help with the healing of skin and stomach ulcers.31 These fats can prevent the multiplication of or even kill Helicobacter pylori, bacteria that are well known to cause stomach and duodenal ulcers. This provides further good news for arthritis patients; many of them suffer from stomach ulcers due to common arthritis medications, especially if they harbor the harmful bacteria in their stomach linings. The omega-3 fats may also have a role in cancer prevention. The risk of both colon cancer and breast cancer seems to decrease when these fats are included in the diet.32, 33, 34 One of my special interests is in gastrointestinal diseases. One problem that I treat in my office on a daily basis is a disease called ulcerative colitis. Ulcerative colitis is an autoimmune disease wherein the body attacks the colon, causing ulcers, inflammation, fevers, bleeding, diarrhea, and abdominal pain. It tends to relapse frequently; that is, it will subside for awhile and then flare up again. A four-month long study included 23 patients with chronic active ulcerative colitis.35 About one-half of the patients were given three grams daily of eicosapentaenoic acid (EPA), an omega-3 fatty acid. The other group received look-alike pills that had no medicinal effects (called a placebo). After four months, the two groups were switched to the opposite treatment. The results of the study are summarized in Figure 4: EPA (an Omega-3 Fatty Acid) is Effective for Ulcerative Colitis.
Notice that only three out of ten who took the placebo had remission, and all three later relapsed. The story was remarkably different for those taking omega-3: 10 out of 13 experienced a remission of their disease. Even though slightly more than 50 percent of those with a remission later relapsed, some remained disease-free. Unfortunately, cow's milk and many infant formulas lack certain omega-3 fats that are necessary for optimal brain and eye development. Human breast milk, however, has abundant omega-3 fats and may be one reason why infants raised on human milk do better on intelligence tests than their formula-drinking counterparts.36, 37, 38 An omega-3 fatty acid deficiency can also cause depression or even over-aggressiveness in adults.39 With all the wealth of information demonstrating the benefits of omega-3 fats, it might seem that we should at least put a little fish on our dinner plates. But before final recommendations are issued regarding our personal eating habits, we need to explore more fully the "down side" of fish consumption.
Fish and Fish Oil's Bad Side
Fish oil capsules and other fish oil supplements may not offer the benefits of fish oil in its fresh, natural state. Although the fresh omega-3 polyunsaturated acids tend to help platelets and decrease heart disease risk, oxidized omega-3 fatty acids may do the opposite.40 While on the shelf, natural fish oil can become oxidized,41 and therefore very damaging to arteries due to the oxidized cholesterol. Furthermore, EPA (the omega-3 fatty acid present in fish) readily oxidizes to form peroxides, which are powerful free radicals. For anyone who is concerned about avoiding free radicals, giving up fish would be a logical first step. Fish oil supplements may not offer the heart and blood vessel benefits consumers anticipate. The Nutrition Committee of the American Heart Association has recently gone on record stating, "fish oil capsules cannot be recommended at this time¡¦to prevent disease of the coronary arteries."42
There are several important potential problems with eating fish and fish oil. These problems have not been well publicized. They are listed in Figure 5: Problems with Fish and Fish Oil.
The items in Figure 5 deserve further comment:
Fish oil can raise blood sugar in adult-onset diabetics. A University of California study found that these so-called Type II diabetics experienced a nearly 20 percent rise in their fasting blood sugar levels after taking fish oil for a mere four weeks.43 The reason for the diabetic worsening appears to be EPA; this omega-3 fat may reduce insulin production in diabetics.
A diet very high in fish or fish oil can dangerously increase the blood clotting time.44 Eskimos, although they have less heart disease, have more hemorrhagic (bleeding) strokes than Americans do.45 Apparently, their fish-rich diet causes such an impairment of platelet function that they bleed more easily.
Fish oil is expensive, especially in capsules. Researchers used 15 capsules of fish oil daily for six months in order to decrease re-accumulation of atherosclerosis following angioplasty.46 Retail prices are about $9.00 for 100 capsules. This translates into over $245 for the six month course of therapy. Continuing on the regimen would cost around $500 per year.
Large amounts of fish oil used as a supplement may upset your vitamin balance.47 Dr. Jack Yetiv has pointed out that high doses of fish oil may cause very high levels of Vitamins A and D-so high that they could be toxic. Both of these vitamins are fat-soluble nutrients that are necessary for life and health in appropriate amounts. However, either can cause poisoning-and in some cases-death, if levels build up too high in the blood. On the other hand, a diet rich in fish oil can cause Vitamin E deficiency.48
The large amounts of fish oil that have been used in many studies can lead to a significant increase in body weight. These preparations are extremely high in fat and calories.49 Yetiv estimated a person could gain up to 24 pounds in a year if he took as much fish oil each day as some studies were using.50
Seafood is a reservoir for infectious diseases. There are about 113,000 reported cases of food poisoning from contaminated seafood each year in the U.S.51 This is clearly an underestimate, since many incidents are not reported. Seafood contributes to a disproportionately high amount of food poisoning outbreaks. Statistics suggest that reported outbreaks (episodes of food-related illness where more than two people are affected by a commons source) might be as much as 15 or more times likely to occur with seafood than with beef, poultry, or pork.52 Raw shellfish in particular (such as oysters, clams, and mussels) have a dismal record. About 20 million Americans eat raw shellfish, which account for more than 90 percent of seafood poisoning cases.53 When raw shellfish is eaten, the whole living creature is consumed complete with its gastrointestinal tract. That would be equivalent to plucking a live chicken and eating it whole, guts and all. What's more, shellfish feed by filtering two to three gallons of water an hour. That means they take in whatever is floating by-not only plankton and other food, but viruses, bacteria, mercury, and who knows what else? Unfortunately, shellfish are commonly harvested from coastal waters that have been contaminated with human sewage. Infection with salmonella, campylobacter, the Norwalk virus, Vibrio vulnificus (which alone kills 10 to 15 people each year), and other infectious diseases can result. Even well-cooked shellfish can infrequently cause serious or life-threatening illness. Two such maladies include paralytic shellfish poisoning and neurotoxic shellfish poisoning.54 Shellfish are not the only seafood that present causes for concern. For example, over 400 different species of reef fish carry the risk of transmitting ciguatera poisoning, which is the most common fin fish poisoning in the United States.55 Some 8000 Americans a year are made ill by the ciguatera toxin. Affected fish, such as red snapper, amberjack, barracuda, and grouper, look and taste normal but can produce a disease that causes digestive symptoms such as nausea, abdominal cramps, and diarrhea. Later a "pins and needles" sensation occurs around and inside the mouth and in the hands and feet. Victims often experience "temperature reversals" where hot things feel cold and more likely, cold things feel hot. While the effects of ciguatera usually last about two weeks, as many a 20 percent of all victims will still have some symptoms at six months and five percent at two years.56 Nerve and vision involvement, heart and joint problems, and sometimes even death can occur.57 Scombroid poisoning is less common and less serious than ciguatera. Symptoms include a tingling and burning sensation around the mouth as well as diarrhea, cramping, and an itching rash. Most cases in the U.S. occur from mahimahi or fresh tuna.58 Sushi, raw fish Japanese-style, also presents unique risks. Roundworms, flatworms, tapeworms, and flukes can all be transmitted by these sea food items.59 What about the reduction in water pollution? Has it now made it safe to eat fish? Do not be misled by impressions that water pollution is fast becoming a thing of the past. Although regulatory bodies may be keeping a closer eye on toxins released by industries, there are even more important non-industrial concerns regarding infectious disease agents. For example, in some locations large numbers of septic tanks have been constructed in unsuitable soil near water sources. The resulting overflow has been known to cause such severe pollution that shellfish beds have been officially closed.60 Other sources of microbial water contamination include animal wastes from agriculture and municipal wastewater discharged by publicly owned treatment facilities.61
Perhaps most importantly, fish 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.62 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 have the highest levels of mercury.63 Despite the popular belief that fruits and vegetables have the greatest risk of pesticide contamination, the FDA's research reveals that domestic fish products contain significantly more pesticide residues than domestic fruits, grains, or vegetables.64 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).65
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.66 In the U.S., about 600 pesticide ingredients are used, accounting for some 800 million to 1 billion pounds per year.67 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."68
How do fish become exposed to pesticides? As previously mentioned, one big cause is agricultural runoff. When a farmer sprays his fields, a portion of the chemicals will be washed off into neighboring creeks and streams, and ultimately into rivers and oceans. Sewage overflows, 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 6: Swimming Prohibited, are erected at some swimming 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 "calling wolf." Illnesses such as gastroenteritis, dysentery, hepatitis, and others can result from swimming in contaminated water.
The risk of spending time in the waters on our globe is highlighted by a disturbing trend among fish. Fish have more cancer now than 50 years ago.69 A Canadian biologist, Ron Sonstegard, has examined bottom-dwelling fish in the Great Lakes and the rivers that feed them. In every fish species he has found tumors-often malignant ones.70 For example, 30 percent of the bullheads 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: problems with cancerous fish have turned 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.71 Although Craig's insights may not necessarily prove human risk, they surely raise serious concerns about the human health hazards from the "epidemic" of cancers in fish.
Rather large amounts of fish die in droves every year throughout our country simply due to pollution itself. The Environmental Protection Agency (EPA) of the U.S. government has attempted to trace the amount of fish kills due to pollution as well as other causes. Figure 7: Number of Reported Fish Kills Caused by Pollution reports the number of fish kills proven to be due to pollution by state in 1993.72 Each fish kill usually represents literally thousands of fish. The EPA admits that these figures greatly underestimate the actual number of fish kills, since 15 states did not report or keep track of their fish kills. Also, many additional fish kills occur but 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.73 Unfortunately, many fish that are ill and suffering from these pollutants but have not yet died are caught by fisherman, taken to market, and consumed by humans that think they are eating healthy food.
Health Problems from Contaminated Fish
Perhaps the greatest dangers from fish are those faced by nursing infants. One study found that those who consumed contaminated Great Lakes fish experienced reproductive complications. These included alterations in birth size, gestational age, changes in neonatal health status, and effects that persisted into early infancy.89 As a result of these risks, some have suggested that infants should not be breast-fed because of the cancer risk. Although this may seem to make sense in our toxin-contaminated world, a better alternative may be avoiding the major sources of those toxins. Other research suggests that the bottle-feeding strategy may backfire. There is evidence that breast feeding in and of itself decreases breast cancer risk. A 1994 study found that daughters who were breast fed by their mothers had 25 percent less breast cancer.90
For convenience, a summary of previously mentioned contamination compounds found in fish is shown in Figure 9: Fish Contamination Compounds. Possible links to cancer from contaminated fish are summarized in Figure 10: Evidence Linking Fish Contamination to Cancer. PCB contamination of fish has been well documented. The evidence of the deleterious effects of PCB on the human reproductive system is summarized in Figure 11: PCB and the Reproductive System.
Get the Omega-3 Benefits Without the Risks of Eating Fish
There is a way to have the benefits of the omega-3 fatty acids without having to eat fish, fish oil, or expensive capsules. There is a way to bypass the cholesterol and toxins that come with the animal-derived omega-3. The way is so simple, but it is not getting the publicity it deserves. We can obtain the benefits of omega-3 fatty acids from a plant fat called linolenic acid. The human body can actually make the well-studied eicosapentaenoic acid (EPA) from linolenic acid. Linolenic acid is itself an omega-3 fatty acid and is an essential component of the human diet.
Linolenic acid is different from linoleic acid. The critical difference is in the letter "n" that is three letters from the end. Students of biochemistry may remember the difference between these very different fats by noting that the one with the "n" three letters from the end is an "n-3" fat (another technical name for an omega-3 fat). On the other hand, the fat without that critical "n" is linoleic acid, called omega-6 fatty acid, and is found in corn oil and safflower oil. Many common plant foods are rich in linolenic acid. Some of them are listed in Figure 12: Plant Foods Containing Omega-3 (Linolenic Acid).92
Note that the highest source of linolenic acid is flaxseed oil (also called linseed oil). One tablespoon has over 7500 mg of linolenic acid. One-quarter cup of English walnuts contains 1700 mg of the omega-3 linolenic acid. One tablespoon of soybean oil has more than 900 mg. Even one cup of canned spinach contains about 350 mg. We do not normally think of spinach as having much fat, but it is an excellent source of omega-3. Today's generation of mothers can now tell their children to eat their healthful spinach with added force. Even common foods we eat every day, like a banana, an apple, bread, or potatoes, all make their contribution to our linolenic acid intake.
As we can now better understand the benefits of omega-3 fatty acids, we can also appreciate that it can make a difference where we get them. When adopting a balanced diet of plant foods, we reap the benefits of omega-3 without the toxins, pesticides, and cancer risk inherent in today's fish. Besides enjoying the foods listed above, if you are in need of concentrated amounts of omega-3 fatty acids, try grinding equal proportions of flaxseed and walnuts. We call it "flax-nut butter." It has a texture similar to peanut butter and is quite tasty. Patients suffering from significant coronary artery disease, rheumatoid arthritis, psoriasis, or hypertriglyceridemia may benefit from the higher doses of omega-3 that flax-nut butter can provide.
It is important to point out that most studies regarding the benefits of omega-3 fatty acids have focused on the one fatty acid that has been considered in this chapter-EPA. Many researchers seem to ignore that EPA is not an essential fatty acid. We have already identified why it is not essential: our bodies manufacture EPA from the linolenic acid that is found abundantly in the plant foods listed above. The steps by which EPA, eicosapentaenoic acid, is derived from linolenic acid are outlined in Appendix IV.
Studies clearly show that when a person increases his consumption of plant sources of alpha-linolenic acid, blood levels of EPA also significantly increase as expected.93 Another study demonstrating conversion of alpha-linolenic acid into EPA in humans prompted an interesting observation. This study shows that linolenic acid may have unique benefits in itself in addition to the benefits it provides in being converted to EPA.94 Thus, it may be better to eat foods containing linolenic acid rather than those with EPA. In this way, the body can use however much it needs for conversion to EPA while reserving the excess for other beneficial uses. This would also avoid the dangers of an excess of EPA in the bloodstream, which can trigger a stroke due to hemorrhaging.
One study of a diet enriched in alpha-linolenic acid has already suggested that this fat has a role in preventing heart disease.95 A cousin of alpha-linolenic acid, known as gamma-linolenic acid, appears effective in dealing with arthritic conditions.96
Conclusion
As a physician I find deep satisfaction in helping sick folks regain their health and vigor. But there is something equally and perhaps even more satisfying, and that is helping individuals understand how to prevent illness. From all the research we now have on the causes of heart disease, the conclusion is clear: heart disease is largely preventable. Medications have their place, but regarding the prevention of heart disease, the very best strategy is a commonsense vegetarian diet using a variety of fruits, grains, nuts, seeds, and vegetables. Add to this diet a consistent exercise program, a program for stress management, and the other practical lifestyle recommendations in this and the chapters to come. Such a combination will give you the finest program for preventing heart disease or addressing a problem that has already begun.
Remember: anything worthwhile in life takes time. Many people have given their all to make a fortune, but in the process have lost what is most dear and priceless: their health. My wish for you can be best expressed from the Bible, "Beloved, I wish above all things that thou mayest prosper and be in health, even as thy soul prospereth."102
