Sunday, September 16, 2007

Omega 3, Fish and Mercury - Is Fish Safe to Eat?

Omega-3 fatty acids have been reported to have a beneficial effect on cardiovascular disease (CVD) . This effect has been reported in patients with preexisting CVD as well as in healthy individuals. A number of countries (Canada, Sweden, United Kingdom, Australia, Japan) as well as the World Health Organization have made formal population-based dietary recommendations for omega-3 fatty acids.

Foods that are rich in omega 3 fatty acids include fish, canola and olive oil, soy, flax seed, and walnuts. Most of the studies which show the health benefits of omega 3 have been correlated with fish consumption. Omega 3 fatty acids can be categorized into plant-derived omega 3 fatty acids ( -linolenic acid) and marine-derived (eicosapentaenoic acid [EPA] and docosahexaenoic acid[DHA]) omega-3 fatty acids. Typical recommendations for daily intake of linolenic acid are 0.8 to 1.1 g. Recommendations for EPA and DHA are 0.3 to 0.5 g/d and up to 1.2 grams if there is a history of heart disease or cholesterol abnormality.

Fish are the major food source of EPA and DHA. All fish contain EPA and DHA. However, some species of fish may contain significant levels of methylmercury, polychlorinated biphenyls (PCBs), dioxins, and other environmental contaminants. Exposure to PCBs can be reduced by removing the skin and fat from these fish before cooking them; however, because mercury is distributed throughout the muscle it is not possible to remove it from the filet. Fish that are highest in mercury concentration are the large predatory fish such as swordfish, King mackerel, shark, and tilefish. This chart shows the different levels of mercury associated with different types of fish.

The benefits and risks of eating fish vary depending on a person’s stage of life. In general it is advised that children and pregnant and nursing women avoid potentially contaminated fish because this group is at a lower risk for cardiovascular disease but at a higher risk of exposure to mercury. For middle-aged and older men, and women after menopause, however, the benefits of eating fish far outweigh the risks within the established guidelines . Eating a variety of fish will help minimize any potentially adverse effects due to environmental pollutants.

Here's a video about omega 3 from a medical student.

References: Circulation. 2002;106:2747. U.S. Environmental Protection Agency. American Heart Association.

2 comments:

Mel said...

Excellent recommendations. Seafood is such an important part of the diet and is often neglected due to concerns of mercury. The decision of what fish to eat can be a challenge and often contradictory. At the very least, women should know that FDA and EPA have issued advisories about mercury contamination in commonly-sold fish. It’s targeted at women of child-bearing age and kids, and advises no consumption of swordfish, tilefish, shark and king mackerel, and also advises those same target groups to limit consumption of albacore tuna and tuna steaks to 6 oz. per week or less.

The problem is, this information is hard to find and is not usually available where it is most necessary: your supermarket.

Oceana, a conservation group focused on mercury is trying to get major grocery companies to post this government advice at their seafood counters. Thanks, in part to their work, Whole Foods, Safeway stores, and Wild Oats voluntarily agreed to post the FDA’s recommendations and they have had positive responses from customers and no loss in seafood sales. But other companies like Wal-Mart, Costco, and Giant have refused to do so. Oceana has a list of which companies care about their customers’ health enough to post this advice, as well as a list of companies that don’t. You can get the Green List and Red List at their website.

Anonymous said...

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