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Angela in Nova Scotia submitted three questions ~ this is the first:
The Fish/Mercury Conundrum: We’ve all heard about the benefits of including fish in our diets. The American Heart Association now recommends two-to-three servings of fish per week. Why? Lean protein, for starters. The big deal, however, is the omega-3 fatty acids abundant in fish, which aid healthy brain and vascular development in babies and confer protection against heart attacks and strokes in adults. They have also shown potent healing properties in connective tissue disorders and cholesterolemia. Omega-3s are not blood-thinners; they are blood de-sticky-fiers. Brand new word, what do you think of it? :-D In other words, type Os need not worry that their natural propensity toward more copious bleeding would be magnified by eating more fish. It is the tendency of platelets to clump or clot, rather than blood plasma-to-cell ratio, which is affected by these EFAs.
Fatty, cold-water fish like salmon, sardines, mackerel and lake trout are the recommended species due to their relatively low tested mercury levels. The FDA’s cutoff point is 1 part per million, 1/10th the levels found in mercury-related disease. Tuna is considered a fence-sitter: the average reading is around .2 ppm methyl mercury. Interested parties disagree as to whether this fairly low level should place tuna in the OK category or the red-flag zone, since it (canned tuna particularly) is such a popular and frequently eaten food in the U.S. The big predators like shark and swordfish can accumulate higher levels, sometimes reaching 1 ppm, and conservative health professionals warn against eating them more than once per month.
Pregnant women in particular should choose wild fish, both freshwater and small saltwater dwellers, over the big oceangoing migrators, because the developing fetus is extremely vulnerable to nervous-system damage from mercury in the diet, air and water – and the older and larger the fish, the higher the mercury can climb. Farmed fish are usually raised under conditions you don’t want to know about, and with feed you wouldn’t even want in your compost. Try your darnedest to get wild catches, and research the environment of your freshwater choices: they pose a concern only if caught near areas of industrial pollution.
The fish recommendations in Peter's books are made with clean, low-mercury specimens in mind. They are based on biochemical properties, rather than potential environmental poisoning. So the best approach is to evaluate your seafood sources. Fish from the eastern seaboard and major rivers of the United States and parts of Central and South America are more likely to push the mercury levels than are those caught off the coasts of less industrialized areas of Canada and Alaska. :-)