Eating deep sea fish – helpful or harmful?

Author: Ms. Agnes Lam, Nutritionist of HK BioTek

It was clinically proven in a number of medical researches that eating deep sea fish can reduce the risk of coronary heart diseases. Experts have further stated that by eating fish three times a week, one can reduce the mortality due to chronic diseases by up to 25%. However, as mercury can be found in most fish, one risks excessive intake of mercury by eating too much deep sea fish, leading to chronic poisoning. So, is consuming deep sea fish helpful or harmful? Which types and in what amount of deep sea fish should we eat to maximize the benefits and avoid excessive intake of mercury?


Eating fish can reduce the death rate of chronic diseases which may be related to the fat content of fish, which is significantly lower than red meat, e.g. beef and pork, and its omega-3 fatty acids.

1 ounce (28.4grams) of fish contains roughly 1-3 grams of fat, of which only 25-30% are saturated fat (NB. Saturated fat can increase the ‘bad’ cholesterol level in our body and thus, increase the risk of coronary heart diseases), compared to up to 50% or more in other red meats, thereby reducing the risk of coronary heart diseases. Furthermore, omega-3 fatty acids, such as EPA is anti-inflammatory, which can reduce the risk of blood vessel blockage caused by inflammatory; aid cholesterol metabolism and lower the ‘bad’ cholesterol level; while DHA is beneficial to the retina and brain’s health and development.


An independent US organization, GotMercury.Org, reported that the Tuna sushi samples found in Los Angeles contained mercury levels that were 80% higher than the FDA recommendation, with some samples not even suitable for human consumption, raising concerns amongst fish lovers. Mercury is an element that can be found naturally in soil, rocks and coal, and passes into water through Coal-fired power plants and other sources. Fishes take in mercury through eating planktons, and the mercury cannot be metabolized or removed in their body. Therefore, when the deep sea fish eat the small fishes, the mercury stored in the small fishes would be accumulated in the huge fish. The larger the fish, the higher the mercury level. Excessive intake of mercury can cause chronic poisoning, and potentially damage the central nervous system, causing damage to brain function. Excessive intake of mercury in pregnant women may also affect the nervous system and brain development of the fetus.

So, is consuming deep sea fish helpful or harmful? Stay tune to our next newsletter, where we’ll discuss the issues of how to choose deep sea fish, and the recommended intake level.