By Julie Redfern, R.D., L.D.N.
Heard any good fish stories lately? Here's one: Certain fats in fish and seafood may be fantastic for your health — they may even prevent heart disease.
Now here's a bad fish story: Some fish may contain high levels of harmful toxins. Moreover, our hearty appetite for the fruit of the sea has helped to create a new fish-farming industry. While this makes fish more readily available, large-scale production has brought to light similar problems faced by corporate farming, including the spread of disease and negative environmental impact.
So, should you go for the catch of the day or sail on for better waters?
Seafood is chock full of lean protein, zinc and heart-healthy fats. These heart-healthy fats may lower the risk of heart disease when substituted for meat. Seafood is a particularly great source of omega-3 fats called EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). EPA has heart-protective properties, and DHA benefits the nervous system.
Omega-3 fats are essential to good health, and since we cannot make them in our body, we must get them from our foods. The most efficient way for your body to get these fats is to eat fish and seafood. Do you need more reasons to go for grilled halibut instead of the porterhouse? The friendly fats in fish and seafood:
Our fish story gets more complicated, however. Because of contaminants in fish and seafood, especially mercury, some fish may be, alas, harmful to our health.
In addition to those good fats, fish and seafood also can contain a not-so-healthy toxin, mercury. While most fish and seafood contain traces of mercury, those near industrialized cities, or larger predator species such as swordfish, mackerel and shark, usually contain more. Skinning, trimming and cooking fish does not reduce the toxin concentration since it is distributed throughout the muscle.
High levels of the metal can accumulate in brain tissue and cause neurological problems. Your body has a hard time getting rid of it — a bit like cleaning up a toxic waste site. Pregnant and nursing women should be especially careful. High levels of mercury may affect the sensitive nervous system of a developing fetus (methylmercury easily crosses the placenta). Equally, infants or very young children who are breast-fed can absorb mercury through their mothers' milk.
But we are not out of the deep end yet. To complicate our decision-making even further, we must consider farm-raised versus wild fish.
Like cattle in pens, fish are bred and raised in contained environments, typically close to the shore of a lake or river. To help keep up with high demand for seafood, the farm-raised fish business (or aquaculture) has soared. Is there a difference in the quality of fish, levels of omega-3 fats, and levels of mercury in farm-raised versus wild fish?
All fish, whether farm-raised or wild, contain omega-3 fats, but the levels vary with environmental factors such as their species and type of feed. Farm-raised species usually have lower levels of mercury, but may contain other contaminants. Farm-raised fish can breed illnesses that warrant the use of antibiotics. The feed is not the same as that of wild fish — additives are used in the feed, and the flesh is dyed to help the fish obtain the usual pink color consumers find familiar. The farms are packed tightly, which lowers the fish's immunity to parasites. Excrement and excess food pollute the ocean floor. If a farm fish escapes, these ill fish can potentially contaminate their wild companions.
Fish farmers are already improving methods of farming to fix some of these issues. Some have started using closed, circulating tanks that redirect wastes for future use. Fish farmers also are looking at using more eco-friendly feed.
The bottom line: There is a place for both farm-raised and wild fish in our future as the stocks of wild fish are replenished and farming methods are improved. If you are concerned about this issue, be sure to ask your grocery store or market about the sort of fish they stock.
Julie Redfern, R.D., L.D.N. is a registered dietitian in the nutrition consultation service at the Brigham and Women's Hospital. She specializes in nutrition counseling for the Obstetrics and Gynecology Department. She is a graduate of the University of Vermont, and completed her internship at the University of Cincinnati Medical Center.