Fish: Health and Harm

Fish is one of the healthiest ingredient you can add to your diet. Rich in Omega 3 and Omega 6 fatty acids, it has been proved to be one easy way to cut down on bad cholesterol. To help improve heart heath, it has been suggested that at least two 6 oz servings (about the size of a deck of cards) of fish be included in your diet every week.

Why fish should be incorporated in your diet:

• Are a rich source of the essential fatty acid, omega-3, which cannot be synthesized by the human body.
• Produce anti-inflammatory prostaglandins like EPA (eicosapentaenoic acid), which prevent platelets from sticking together, and so prevent formation of blood clots.
  
• Reduce incidence of arrhythmic heart beat, atrial fibrillation.
  
• Increase ratio of HDL to LDL.
• Protect against stroke and heart attack (most beneficial when at least 5 servings are consumed per week, though benefits can be observed when as little as 1 to 3 servings are consumed per month)
• Offers protection from AMD (Age-related macular degeneration, causing loss of fine vision and blindness).
• Lowers risk of dry eye syndrome (mostly studied in women)
• Protection against Alzheimer's disease (60% decrease in incidence if fish is consumed once a week).
• Increases cognitive function and memory.
  
• Some studies suggest fish may protect against sun burn, and may also help reduce risk of skin cancer.
• Protect against cancers of the ovaries, esophagus, stomach, intestines, mouth, pharynx, colon, rectum, pancreas, breast, prostrate. Salmon may be most beneficial since it also contains another anti-carcinogenic agent: Selenium.
  

There has been a lot of confusion regarding consumption of fish and birth defects caused by bio-magnification of mercury. Some facts about mercury and fish...

Because of our carelessness and the dumping of industrial wastes into our oceans, there has been a contamination of mercury. Our problems with this metal started when it started increasing in concentration each time smaller fish eaten by a bigger fish deposited its mercury in the bigger fish (bio-magnification). Mercury in water, with the help of certain bacteria, is converted into methyl mercury which is easily absorbed by human beings. This absorbed methyl mercury is dangerous because it acts as a very potent neurotoxin. In other words, it effects the brain and nervous system of mammals. This is particularly dangerous in cases where the nervous system is in a developmental stage, like in young children and in pregnant women.

Mercury toxicity is manifested in children by a delay/difficulty in walking/talking, attention deficit, learning disorders etc. In adults, it can result in infertility, memory loss, and may also cause some cardio-vascular problems.

So, what are the precautions you need to take while selecting your fish to minimise your consumption of mercury? First point to remember, small fish have lesser mercury content. So, always try to pick smaller fish. The other important point is to eat different varieties of fish. As different fish have different mercury concentrations, mixing and matching them will ultimately result in a better balance. Recently, it has also been suggested that the best thing to do would be to find a geographic area with lesser mercury levels in the ocean and try to consume wild fish from that region. Try to avoid wild fish caught in heavy industrial areas, as there is a greater possibility for fish in these areas to have a higher mercury concentration.

Finally, I would like to include a list of fish and the levels of mercury:

Class I: Highest Mercury Levels:
Shark: 0.99 ppm (0.90)
Swordfish: 0.97 ppm (0.70)
Tilefish (golden snapper, golden bass): 1.45 ppm (0.80)
King mackerel (called vanjaram in Andhra): 0.73 ppm (0.34)

These fish should not be consumed by young children, women planning to become pregnant, pregnant women, or nursing mothers. All others can consume up to 7 oz of these fish PER WEEK.

Class II: Moderate Mercury Levels:
Fresh or frozen tuna: 0.38 ppm (0.24 to 1.28)
Red snapper: 0.60 ppm (0.27)
Orange roughy: 0.54 ppm (0.002)
Lobster: 0.31 ppm (0.07 to 0.41)
Grouper: 0.55 ppm (0.21)
Halibut: 0.26 ppm (o.40 to 1.00)

Again, young children, women planning pregnancy, pregnant women, and nursing mothers should limit their consumption of these fish. It has been suggested by the American Heart Association that they consume a maximum of 12 oz of these fish PER WEEK. Other people can consume up to 14 oz of these fish PER WEEK.

Class III: Low Mercury Levels:
Fresh and frozen salmon: 0.01 ppm (0.68 to 0.73)
Herring: 0.04 ppm (1.71 to 1.81)
Flounder or sole: 0.05 ppm (0.43)
Scallops: 0.05 ppm (0.05)
Catfish: 0.05 ppm (0.15 to 0.20)
Pollock 0.06 ppm (0.46)
Crabs: 0.06 ppm (0.34 to 0.40)
Cod: 0.11 ppm (0.13 to 0.24)
Canned tuna, light: 0.12 ppm (0.26 to 0.73)
Mahi-mahi: 0.19 ppm (0.12)

Values in parenthesis denote the quantity of omega-3 fatty acids per one 3 oz serving of the fish. Values in ppm indicate the concentration of mercury.

Interesting point: Mercury levels can be controlled by reducing intake of fish high in mercury for about 6 months.

Shrimps, Oysters and Clams have been shown to have mercury concentration below detectable levels.

References:
American Heart Association
World's Healthiest Foods
WebMD