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Understand the ratio between selenium and mercury. Tuna, salmon and sardines are among the best fish to eat.

Miami Herald October 19, 2015

October 19th, 2015


What words come to mind when thinking about fish?

Lean protein, omega 3 fatty acids, and tasty would be among the top three.

But concerns about mercury have kept many people from reaping the health benefits so abundant in fatty fish. Clarity is now coming to this topic.

During the recent meeting of the Academy of Nutrition and Dietetics, I heard Dr. Nicholas Ralston, a mercury researcher, talk about how the mineral selenium has been too often overlooked in the fish/mercury discussion. Selenium is an essential trace mineral that functions as an antioxidant and promotes a healthy immune system. Selenium also helps fish get rid of stored and dangerous methyl mercury. So the more accurate way to evaluate a fish for safety is to look at the selenium-to-mercury ratio.

Fish with the highest selenium-to-mercury ratio, and thus safest to eat, are albacore, yellowfin and skipjack tuna. The traditional advice of limiting albacore tuna to six ounces a week needs a revision. Chinook, sockeye and coho salmon also have a favorable ratio.

Small healthy fatty fish, such as sardines, anchovies and herring, are very low in contaminants and not a safety concern. The most concentrated vegetarian source of selenium is Brazil nuts. Fish to avoid are pilot whale (not a problem), tarpon and swordfish.

It is the omega 3 fatty acids that make fish a desirable diet addition. Strong evidence has shown that fish consumption lowers risk of cardiac mortality, lowers triglycerides and blood pressure and keeps blood from forming clots. About 250 mg/day of the omega 3 fatty acids DHA+EPA provides heart benefits. This translates to about 1-2 servings a week of salmon, tuna, anchovies, herring, sardines or trout.

I hope anyone who gave up a favorite tuna fish sandwich feels comfortable putting it back on the plate.

Sheah Rarback is a registered dietitian on the faculty of the University of Miami Leonard M. Miller School of Medicine. Follow her on Twitter @sheahrarback.

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