Try to eat less of these types of fish, as the heavy metal content may exceed the standard!

Chinese people like to eat fish, but with the improvement of living standards, people's requirements for food safety are getting higher and higher. Many people are worried about whether fish and aquatic products will be contaminated by heavy metals, such as the risk of mercury pollution. How should we choose fish and how to eat it healthier? Let's answer these questions one by one~

The benefits of eating fish are not just for brain health

As a type of "white meat", fish has lower calories and saturated fat content than pork, beef and mutton, and relatively higher content of minerals such as calcium. It can be used as a high-quality protein source during weight and fat loss periods.

Moreover, fish meat is rich in glutamic acid, aspartic acid and other umami amino acids, which give fish meat its own umami flavor. This means that when we cook fish, we don't need to go through deep processing with heavy oil, heavy salt and high sugar. We can just steam or cook it in soup to make it delicious and tempting.

In addition, many fish (especially fatty marine fish and some freshwater fish) contain high levels of unsaturated fatty acids such as DHA, which are beneficial for promoting the development and health of brain cells and visual cells. They are very suitable as a good food source for daily supplementation of DHA. They are highly recommended foods for infants and young children whose brains are in a rapid development period, the elderly and young people who need DHA supplements.

Comparison of nutrient content between fish, pork and beef

In addition, the vitamin D content in many fish is not low, while the vitamin D content in other common foods is not high. For people who lack sunlight and vitamin D in food, it is very suitable to eat more fish.

Does fish contain heavy metals?

Which fish have higher levels of heavy metals?

Some heavy metals in water, such as mercury, lead, arsenic, and cadmium, can be continuously enriched in fish bodies through water bodies or algae containing heavy metals, and the metabolism time is very long.

In the past, people believed that large deep-sea fish were more susceptible to heavy metal pollution than freshwater fish. This conclusion makes sense and is supported by relevant research results [1]. However, the heavy metal pollution in fish is also related to factors such as different sea areas, fish species and age.

Globally, there are some general rules:

Carnivorous fish have higher levels of heavy metals than omnivorous and herbivorous fish;

Large fish have higher levels of heavy metals than smaller fish;

Older fish had higher levels of heavy metals than younger fish.

For example, the “not recommended” (high mercury content) category listed by the U.S. Food and Drug Administration includes large carnivorous fish such as shark, swordfish, tilefish, bigeye tuna, marlin, etc. [2]

Different sea areas also have an impact on the metal content in fish weight.

According to a survey, in my country, the mercury content in wild fish in the East China Sea and Bohai Sea is higher than that in farmed fish; the mercury content in farmed fish in the South China Sea is higher than that in wild fish[3]. At the same time, in this survey, carnivorous fish such as grouper, golden threadfish, catfish, and mandarin fish showed higher mercury content, which is also in line with the general rule mentioned above.

The Hong Kong Food Safety Center also has a warning about the mercury levels in fish, which also lists carnivorous fish with high mercury content, such as golden eye snapper, swordfish, tilefish, bigeye tuna, bluefin tuna, swordfish, shark, etc. This is similar to the "not recommended for consumption" category given by the US Food and Drug Administration [4].

Furthermore, we would like to remind everyone that even for the same type of fish, you should avoid choosing ones that are too heavy. This is mainly because a larger weight means that the fish is older. Not only is the meat not necessarily tender, but it is also easy for it to accumulate more heavy metals through eating and drinking.

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However, everyone can rest assured that the above survey results also point out that the mercury content in my country's aquatic products is generally far below the national standard limit.

Considering that the fish intake of the Chinese population is not up to standard, the daily mercury exposure caused by the intake of aquatic products by the entire population is generally lower than the tolerable weekly intake of methylmercury from food of 1.6 μg/kg body weight published by the Joint Expert Committee on Dietary Exposure and Food Additives, and the health exposure risk is generally at an acceptable level [3].

Whether it is the U.S. Food and Drug Administration, the Hong Kong Food Safety Center, or the Chinese Residents' Dietary Guidelines, the low-mercury, high-DHA fish recommended include salmon, sea bass, sardines, anchovies, yellow croaker, tilapia, etc. Some shellfish also fall into the low-mercury safety category, such as clams, crabs, oysters, scallops, etc., which are inexpensive and can also be chosen.

Want to stay away from heavy metals

There are also some rules for eating

In addition to being familiar with which fish may have higher levels of heavy metals, there are also some tips when cooking and processing fish to minimize our risk of ingesting heavy metals.

1. Try to avoid the several large fish species not recommended above

2. Combine with some ingredients that promote the discharge of heavy metals from the human body

The human body has the ability to remove and excrete heavy metals. As long as you do not eat fish with high heavy metal content for a long time and in large quantities, the possibility of causing harm is generally not great. If you can add some foods that promote the excretion of heavy metals by the human body during the cooking process, such as coarse grains and fruits and vegetables rich in dietary fiber, you can better prevent harm.

3. Diversify your food

We can fully utilize the advantages of food diversity, which will not only reduce the use of fish that may contain heavy metals, but also fully utilize the health effects of different types of nutrients in different foods and the cooperation between different nutrients to minimize, share and offset the health risks that may be caused by heavy metal intake.

For example, if we are worried that the presence of heavy metals will harm the brain and nervous system, we can eat more foods that are beneficial to the health of the brain and nervous system, such as salmon rich in DHA, plain nuts, etc. If we are worried that heavy metals will increase the metabolic burden on the liver, we can eat more fresh fruits and vegetables rich in vitamin C.

In short, food diversity has only benefits and no harm, whether it is in terms of enriching nutrition, preventing chronic diseases, and combating the health hazards of heavy metals.

Finally, the intake of fish should also be limited. According to the Chinese Dietary Guidelines, it is recommended that normal adults eat fish twice a week, about 300 to 500 grams. It is better to steam fish and avoid frying or grilling as much as possible to avoid destroying the unsaturated fatty acids in the fish and increasing the content of carcinogens due to frying or grilling.

References

[1] Ye Haimei, Wu Yongning. Comparison of heavy metal indicators in fish and processed products [J]. Chinese Journal of Food Hygiene, 2009, 21(3): 273-276.

[2]https://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm115644.htm

[3]Xu Xi, Yan Chonghuai. Analysis of total mercury pollution characteristics and health exposure assessment of aquatic products in China[J]. Chinese Journal of Food Hygiene, 2022, 3(17): 104-109.

[4]https://www.cfs.gov.hk/sc_chi/index.html

Author: Wang Lu, registered dietitian

Reviewer: Ruan Guangfeng, Director of Science and Technology Department, Kexin Food and Nutrition Information Exchange Center