What’s Hiding in the Water


We are learning more and more about our everyday exposure to heavy metals and that a major dietary source can be from the seafood we consume. For an active seafood friendly vegetarian like myself cutting down on fish means cutting down on a lot of protein and healthy fats--something I’m not too interested in doing. I thought I should get the hard facts on what's really hiding in the water--what the highest mercury containing seafood sources are and what some healthy alternatives may be. 

Firstly, what is so bad about mercury anyway?  
Well, high doses of methylmercury (the type of mercury that can bio-accumulate in organic tissues) have been known to cause a wide range of adverse health effects. The severity of the adverse effects is largely dependent on the magnitude of the dose and the duration of exposure. It has been shown that the predominant health affects in humans are associated with the impaired functions of the central and peripheral nervous systems. 

In children, elevated methylmercury exposure can potentially cause:
  • Decreased mental functioning
  • Delays in walking and talking
  • Lack of coordination
  • Blindness and seizures
In adults, excessive methylmercury exposure can potentially lead to:
  • Personality changes
  • Tremors
  • Changes in vision
  • Deafness
  • Loss of muscle coordination and sensation
  • Memory loss
  • Intellectual impairment
  • In very extreme cases death


Next, why are fish the primary sources of mercury? 
Fish tend to bio-accumulate methylmercury in their muscle tissues as a result of eating plants and other organisms that contain methylmercury. What happens next is the process of bio-amplification: as we move up the food chain each predator ends up eating higher and higher concentrations of methylmercury, which then bio-accumulates in their muscle tissue. Shark and swordfish are examples of piscivorous fish that are high in the food chain and contain high concentrations of methylmercury.  

So what’s a seafood lover or pescatarian to do?
Tuna is a high protein, low fat food in my diet containing 15g of protein and 3g of fat per serving, which would be hard for me to cut altogether. However, there is good news: according to Health Canada all canned tuna, including albacore, is typically below the Canadian standard of 0.5 ppm total mercury. Some people eat canned tuna every day. If frequent consumers of tuna regularly choose canned albacore (white) tuna, their exposure to mercury could reach unacceptably high levels.

The same concerns do not exist for canned "light” tuna or “light chunk” tuna because it contains less mercury than canned albacore tuna. Various species can be labelled as "light" tuna including skipjack, yellowfin and tongol. There are also various types of tuna used in sushi/sashimi which include:
Seared Ahi Tuna
  • Shiro maguro, Binnaga/Bincho (which is albacore), 
  • Akami: top loin of Bluefin tuna
  • Ōtoro: fattiest portion of Bluefin tuna belly
  • Toro: fatty Bluefin tuna belly
  • Chūtoro: medium-fat Bluefin tuna belly
  • Kihada (maguro): Yellowfin tuna
  • Ahi: Yellowfin tuna
  • Meji (maguro): young Pacific bluefin tuna
  • Negi-toro: Bluefin tuna belly and chopped green onion
As bluefin tuna is a larger fish, it is in the same category as albacore for higher mercury levels and should be avoided.  If you love tuna sashimi try to go for Kihada (maguro) or Ahi tuna instead.

Other fish that tend to contain very low levels of mercury include:
  • Shellfish (for example oysters, clams, scallops, mussels)
  • Salmon
  • Crab
  • Shrimp
  • Trout
  • Herring
  • Haddock
  • Pollock (Boston bluefish)
  • Sole
  • Flounder
  • Lobster
  • Atlantic mackerel 
  • Lake whitefish
Bottom Line:
Even though we know that most fish does contain mercury and that traces of mercury have been measured in other products such as dairy, meats, poultry, eggs, pasta, fruits and vegetables we can choose to limit our overall exposure. We can do this by making educated decisions when choosing which types of fish we eat and how often we eat tuna and other potentially concerning fish.  

Cheers,
Nadia



A long time athlete and health advocate,  Dr. Kumentas’ goal is to help her patients become excited about making positive lifestyle choices in order to enjoy healthier, happier lives.  Her driving force is a passion for healing the whole person on a physical, emotional, and spiritual level using carefully selected natural therapies, fitness, and integrated medicine.  She truly believes in the importance of practising what you preach and investing in your health.  
Dr. Nadia Kumentas practices at Zen Beginnings Wellness Centre in Toronto and has a special interest in dermatology, woman’s health, and pain management.

To learn more about Dr. Nadia Kumentas visit www.DrNadiaKumentas.com or contact her at nadia@zenbeginnings.com.



References:
http://www.hc-sc.gc.ca/fn-an/securit/chem-chim/environ/mercur/merc_fish_qa-poisson_qr-eng.php#ct3
http://www.sciencedaily.com/releases/2010/04/100421075203.htm
http://en.wikipedia.org/wiki/List_of_sushi_and_sashimi_ingredients
Pictures from: www.corbis.com 

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