The Paleo Diet - Loren Cordain [60]
Unfortunately, there’s a downside, and it has nothing to do with fish and seafood, but with our own environment. Fish and seafood are often contaminated with heavy metals, particularly mercury; by polychlorinated biphenyls (PCBs); and by pesticides such as DDT and dieldrin. The places where fish live—oceans, rivers, lakes, and streams—are also the dumping grounds for many of these potentially harmful chemicals. Once in the water, these toxins seep into the sediments and then into the plants. They’re ingested by the tiny animals that form the base of the food chain. Little fish eat plants and tiny animals, and bigger fish eat little fish. Heavy metals and fat-soluble pesticides can become concentrated in older fish, in predatory fish, and in fatty species of fish.
Mercury finds its way into our waterways as a by-product of fuel-burning and through household and industrial wastes. Bacteria in the water convert mercury into the toxic compound methylmercury. When we eat mercury-contaminated fish, we can develop mercury poisoning, which can damage the brain and the nervous system. The good news is that most of the time, the amount of mercury we get from fish is quite small. And the amount of mercury that you can potentially accumulate by eating fish three or four times a week is tiny compared to how much you could get by industrial or occupational exposure.
For healthy people, regular fish consumption poses virtually no risk to brain or nervous system function. It’s safe even for pregnant women and very young children, concludes a comprehensive study conducted by Dr. Philip Davidson and colleagues at the University of Rochester School of Medicine and Dentistry in New York. Their findings, published in the Journal of the American Medical Association, come from a nine-year study conducted in the Republic of the Seychelles, an island nation in the Indian Ocean, where most people eat fish nearly a dozen times a week and have mercury levels about ten times higher than those of most Americans. In fact, no harmful effects were seen in the nervous systems and behavior of children at mercury levels up to twenty times the average American level.
It is a worrisome fact that we live in a polluted world, and most of us are exposed to a host of toxic compounds. However, the greatest risk to your health is not from environmental pollutants, but from heart disease, diabetes, obesity, stroke, and the associated health disorders of metabolic syndrome. Eating fish protects you not only from these diseases but from all causes of death, including cancer. Because fish is one of our greatest sources of omega 3 fats, it can also help prevent depression and improve your mood, as my friend and colleague Dr. Joseph Hibbeln of the National Institutes of Health has shown. In short, fish should be part of your diet.
You should still be prudent when you shop for fish and seafood. Here are a few ways you can minimize your risk of eating contaminated fish:
• Avoid freshwater fish taken from lakes and rivers—particularly the Great Lakes and other polluted, industrialized areas.
• Choose fish that come from cleaner waters, such as the Pacific Ocean and in Alaska.
• Eat mainly smaller, nonpredatory species such as flounder, herring, sardines, sole, pollock, catfish, halibut, and clams.
• Eat big fish—swordfish, shark, and tuna—sparingly. These long-lived predatory fish tend to accumulate more mercury.
Fortunately, over the long run, the Paleo Diet’s many fruits and vegetables