When it comes to eating fish, scientists are finding lots of reasons for people to get hooked.
Regular meals of fish, recent research has suggested, may help protect a person from heart attacks, strokes, some mental illnesses and a host of cancers, and may prevent early delivery in pregnant women.
A recent study reported that diabetic women, who are particularly prone to heart disease, can lower their risk by as much as 64 percent by regularly eating fish. And one new study of dialysis patients even found that fish-eaters lived longer than non-fish-eaters.
Unlike a lot of meats, fish is high in protein and low in calories, and is even able to improve cholesterol. The fattier it is, the better. The perfect food?
Sorry, Charlie.
Too much fish, especially the wrong sort of fish, might be downright dangerous. Many of the world’s waterways are contaminated with mercury, and the toxic metal accumulates in sea life. Generally, the heftier and longer-lived the animal, the higher the mercury level. Mercury is particularly hazardous for young children and pregnant women because it damages developing brains. One paper published last November also suggested that mercury from fish might increase the risk of a heart attack, the very thing that fish consumption is supposed to protect against.
So eat seafood, the experts say, but no need to go off the deep end.
“You don’t have to eat too much fish to achieve the benefits,” says Dr. Ka He of Harvard Medical School.
The secrets behind fish’s protective effects aren’t fully known, but scientists believe the benefit comes from the type of fat that fish have, technically called omega-3 fatty acids. These substances can also be found in certain oils, such as flaxseed oil.
Omega-3 fatty acids appear to have the ability, among other things, to blunt the body’s natural inflammatory process, protect against irregular heartbeats and reduce blood clots. No one is exactly sure how.
While some scientists in laboratories are bandying about test tubes of omega-3, others have been working out the effects of fish consumption itself. Perhaps the largest body of research has examined heart disease.
For decades, researchers noted that populations that eat a lot of fish – such as Greenland Eskimos, Alaska natives and residents of Japanese fishing villages – have low levels of heart disease.
Curious, scientists started looking at the effects of fish consumption in broader groups of people. Studies dating back to at least the 1980s suggested that fish eaters were less likely to suffer heart disease.
Though not all studies found a benefit, the research has been convincing enough that the American Heart Association now officially advises people to eat fish about twice a week.
Until recently, most studies were conducted in men, but new data from studies in women also found a benefit. For example, a study published last year in The Journal of the American Medical Association reported that among women who ate fish one to three times a month, the risk of dying from heart disease was 21 percent lower than among women who rarely ate fish. Among women who ate fish two to four times a week, the risk was 31 percent lower. “I think there’s a general consensus in the cardiology community that eating fish once or twice a week will protect against heart disease,” says Dr. Christine Albert of Harvard Medical School, one of the scientists who conducted the study of women and fish.
The heart specialists may be persuaded, but the cancer experts are waiting for more data.
Studies have suggested that fish eaters might be less prone to endometrial cancer, prostate cancer, and even breast cancer.
For example, one study published in January in the journal Cancer Epidemiology Biomarkers & Prevention found that men who ate fish more than three times a week had a lower risk of prostate cancer. The association was strongest for the most advanced forms of prostate cancer.
Another study of Swedish men and prostate cancer, published in 2001, had similar findings. Men who didn’t eat fish had two to three times the risk of prostate cancer.
But studies haven’t been consistent – some finding that eating fish protects, others suggesting it doesn’t make any difference. The same is true for breast cancer. At least four studies in the United States haven’t been able to find any link, but research in Japan and in Scandinavia has suggested that women who regularly eat fish are less likely to develop breast cancer.
The reason for the dueling data may be that studies usually ask about the frequency of fish consumption, without accounting for the type of fish. Some fish have a lot of omega-3 fatty acids, while others have almost negligible amounts.
“All fish are not created equal,” said Paul Terry, who has conducted studies of fish and cancer risk at Albert Einstein College of Medicine in New York.
For example, a filet of Atlantic salmon from the fish counter contains more than three times as much omega-3 as the McDonald’s Filet-O-Fish pollock sandwich. So a study that includes a lot of people eating fish low in omega-3’s might not be able to detect a benefit, Dr. Terry said.
He noted that many of the studies finding that fish protects against cancer have been conducted in countries where people have a taste for fattier fish.
While stressing that scientists still can’t say whether fish protects against cancer, “the overall evidence gives us some hope,” Dr. Terry said.
Intrigued by the evidence for heart disease and cancer, researchers have recently tried to examine whether fish might protect against other conditions.
Last year, researchers from Atlanta published one of the first studies to examine whether fish-eating dialysis patients might have a lower mortality rate than their counterparts.
Among more than 200 patients followed for three years, those who ate fish were about 50 percent less likely to die in that time.
The study needs to be repeated with more patients, said Nancy Kutner of Emory University, before anyone can say whether seafood might be recommended for those on dialysis. Still, she said, “if I were on dialysis, and I were aware of these findings, I would be sure to include fish in my diet on a weekly basis.”
Fish may also be good for mental as well as physical health, studies have suggested, acting somehow as a “mood stabilizer,” according to a study from New Zealand researchers published last year. Among a cross section of more than 4,600 adults, the scientists found that people who said they never ate fish scored significantly poorer on a questionnaire designed to gauge a person’s mental status. The data took into account the volunteers’ age, alcohol use, income and other known outside influences. Still more recent research has also suggested that fish might help protect against the symptoms of bipolar disorder and depression. One recent study of more than 3,000 adults in Finland found that infrequent fish eaters were 31 percent more likely to have mild to severe depression. “Our results showed a relatively powerful and independent association between fish consumption and depressive symptoms,” the scientists wrote in the journal Psychiatric Services.
Pregnant women might eat fish – carefully – as a way to help protect against premature delivery, Danish researchers suggested last year. They found that about 7 percent of a group who said they never ate fish delivered their babies early, compared with about 2 percent who ate fish at least once a week. Pregnant women and young children, though, are the most vulnerable to the hazards of mercury.
In addition, Dr. Eliseo Guallar of Johns Hopkins School of Public Health published research late last year that found men with higher levels of mercury in their bodies had an increased risk of heart attack.
Dr. Guallar – raised on fish in his native Spain – shares his dietary solutions to the mercury issue: He has given up large fish that are high in mercury content, such as swordfish, and also eats a variety of kinds of fish. Although his studies point to the danger in seafood, he said, “I think it’s very important that the message that fish is good for you gets through.”
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PROBABLE BENEFITS
Doctors have always considered fish good for you. But recent studies have demonstrated its surprising ability to protect against disease.
Regular meals of fish may help prevent:
Heart attacks
Strokes
Heart disease
(nonspecific) Some mental illness
Various cancers
Premature delivery
in pregnant women Fish may promote:
Mental health
Physical health
Longer life for dialysis patients
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OMEGA-3
Scientists are not sure exactly why fish promotes human health, but there is evidence that it is fish’s levels of omega-3 fatty acids. Here is the omega-3 content of popular fish varieties:
Variety of fish/Grams per 3-oz. serving of fish/Amount required for 1 gram per day (in ounces)
Tuna (light, canned)/0.26/12
Tuna (white, canned)/0.7 3/4
Sardines/0.98-1.7/2-3
Salmon (pink)/1.09/2.5
Herring (Atlantic)/1.71/2
Trout (rainbow, farmed)/0.98/3
Catfish (farmed)/0.15/20
Flounder or sole/0.42/7
Oyster (farmed)/0.3 7/8
Shrimp (mixed species)/0.27/11
SOURCE: Circulation
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RISKS OF MERCURY
Because of the dangers of mercury contamination, fish lovers are advised to limit their weekly consumption to two meals of seafood each week.
The Food and Drug Administration says pregnant women should not eat the first four fish on the list at all.
Almost every type of fish has some mercury. These are some of the more popular varieties, listed with their average (mean) amount of mercury.
Other types also have been ranked, but many of those measurements are based on only small numbers of fish, so they have not been included.
Variety of fish/Parts per million (mean)
Tilefish/1.45
Swordfish/1.0
Shark/0.96
King mackerel/0.73
Red snapper (limited sample size)/0.60
Grouper/0.43
Tuna (fresh or frozen)/0.32
Lobster/0.31
Halibut/0.23
Tuna (canned)/0.17
Catfish/0.07
Scallop/0.05
Salmon/ Not detectable
Oysters/ Not detectable
Shrimp/ Not detectable
SOURCE: Food and Drug Administration
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