By the Way, Doctor: A Very Fishy Diet
Health, Nutrition & Wellness - Bruce Bistrain, M.D.
Harvard Health Letters
Q. I read in an earlier issue of the Harvard Health Letter that one of your nutrition experts eats five servings of fish a week. Why so much? And isn't there a risk from the contaminants?
A. I believe research has shown that eating fish has a variety of benefits, but for me, the science came much later than my love of fish did.
I grew up on a potato farm on the East End of Long Island. My childhood home there was on a farm on Bunker Hill that overlooked the ocean about three-quarters of a mile away. A fish factory that processed menhaden, or bunker fish, a small sardine-like fish, into oil and fish meal was about a mile away. In fact, this Bunker Hill -- not the more famous one in Boston, Mass. -- got its name because bunker fisherman used to dry their recently tarred nets in the field.
So early on I learned to love the ocean, fishing, and eating fish.
My family ate potatoes at least once a day during the winter, and fish and shellfish from the great bounty nearby (bluefish, striped bass, flounder, black bass -- to name just a few) at least four times a week.
I grew up to become a researcher in clinical nutrition and have studied how fish oil might be used to treat the critically ill.
In fact, in my early research the oil we used often came from menhaden. Menhaden is also a major source of the oil used to make over-the-counter fish oil capsules.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the two omega-3 fats found in fish, have been shown to reduce the risk of death from coronary artery disease by about 35 percent when consumed in modest amounts.
Modest means a daily average of about 500 milligrams (mg) of EPA and DHA together (not each), which you can get by eating two servings of fish a week -- provided, of course, it's oily fish.
Two servings provides from 3.0 to 4.5 grams of EPA and DHA, and because much of it is stored, that's equivalent to ingesting about 500 mg daily. There's less definitive evidence from epidemiologic studies that omega-3 fats in that amount will reduce risks of such widely disparate disorders as depression, metabolic syndrome, Alzheimer's disease, and some kinds of cancer. The American Heart Association recommends a daily average of 500 mg for prevention of coronary artery disease, and twice that much -- a gram a day -- for people with established heart disease.
In even greater amounts -- 3 grams a day -- fish oil can significantly lower elevated triglyceride levels, another risk factor for coronary artery disease.
If you're taking prescription-strength fish oil -- Lovaza is a brand name -- for triglyceride lowering, then physician monitoring is indicated.
Intake at the multigram level has shown promise as a treatment for inflammatory disorders such as rheumatoid arthritis and inflammatory bowel disease. And research I've been involved in shows that it helps people who are critically ill from conditions like adult respiratory distress syndrome or because they're recovering from major surgery.
As for contaminants, methyl mercury and toxic organic compounds such as polychlorinated biphenyls (PCBs) and dioxin are the ones that have caused the most concern. (Meat and dairy products also contain methyl mercury and toxic organic compounds.)
In 2006, Harvard researchers Dariush Mozaffarian and Eric Rimm wrote a comprehensive review about the risks and benefits of eating fish that was published in The Journal of the American Medical Association, and some of the following information is taken from their review.
Methyl mercury is found in highest concentrations in four types of fish: swordfish, shark, king mackerel, and tilefish (sometimes called golden bass). Because methyl mercury can impair neurologic development and function, these species should be avoided by pregnant women, those who may become pregnant, those who are breast-feeding, and infants.
However, it's still important for the people in these groups to consume two servings of fish per week with high EPA and DHA content, because DHA is an essential nutrient for optimal brain development, which occurs during gestation and early infancy.
The dangers of methyl mercury aren't an issue for adults unless they eat more than five servings of fish a week. Even then, the risk can be managed by limiting intake of the four species with high mercury levels.
The risks of PCBs and dioxin are essentially below the level of detection when consuming store-bought fish, and because these compounds are also found in similar amounts in meat and dairy products, there doesn't seem to be any disadvantage from swapping one good protein source for another. However, there may be advisories about contamination of freshwater fish in certain areas, and these local recommendations should be heeded.
As for my fish-eating habits, I eat salmon more often than I used to and have tuna fish for lunch most days.
Every Thursday, a friend delivers fish -- it's usually haddock, halibut, or cod -- straight from the dock in Gloucester, Mass., a seaport northeast of Boston. And we treat ourselves to lobster once a month.
In conclusion, I'm happy that there's a likely health benefit to my gustatory pleasure of five fish meals per week, but science has played little part in my lifelong choice.
-- Bruce Bistrian, M.D., Beth Israel Deaconess Medical Center
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