It is often mistaken that only marine fish contain DHA and EPA. In fact, freshwater fish are also a good source of these two important fatty acids that are beneficial to the brain and body .

What are DHA and EPA and what are their functions?

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are two important components of Omega-3 polyunsaturated fatty acids, which can prevent cardiovascular diseases and promote brain development.

Prevent cardiovascular disease and promote brain development

DHA and EPA play a key role in the biological membranes in the body and are also the precursors of certain hormones. These two fatty acids have many benefits for adults, such as lowering blood lipids, improving blood circulation, inhibiting platelet aggregation, and preventing atherosclerosis and thrombosis .

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

In addition, DHA is also an indispensable nutrient during the development of infant vision and brain .

The human body cannot synthesize it, and the conversion efficiency is low

Although DHA and EPA have many benefits, humans cannot synthesize them on their own. Some people say that substances such as linolenic acid can be converted into EPA and DHA in the body, but the conversion efficiency is quite limited. Therefore, the best way to supplement is still direct intake, that is to say, fish and aquatic products are undoubtedly the best way to obtain DHA and EPA.

A large number of empirical studies have shown

Many studies have shown that adequate intake of EPA and DHA can help reduce the risk of chronic diseases such as cardiovascular disease, stroke, and inflammation.

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

A study involving 170,231 subjects showed that consuming 20g of fish and foods rich in EPA and DHA per week could reduce the incidence of heart disease by about 6%.

Another study involving 380,000 subjects also pointed out that EPA and DHA have a positive effect on the stability of heart rhythm , and consuming 300g of fish per week reduces the risk of stroke by about 6%. Considering that this nutrient cannot be adequately supplemented in many dietary supplements, 6% is still very high quality.

Optimal intake of EPA and DHA

According to the recommendations of the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), adults should consume 250 mg of EPA and DHA per day.

For pregnant and lactating women, the intake should be appropriately increased. It is recommended to consume 300 mg EPA + DHA, of which DHA is recommended to be no less than 200 mg .

Freshwater fish also contain DHA and EPA

In fact, fish, like humans, cannot synthesize DHA and EPA on their own and need to obtain them from the food chain. Both freshwater and marine fish contain DHA and EPA.

Data source [1-9] Source: Gu Zhongyi

Even farmed fish are enriched with these fatty acids by eating feed containing EPA and DHA, such as seaweed powder and dried powder made from deep-sea fish scraps. Although marine fish generally contain more EPA and DHA, some freshwater fish are also rich in these ingredients, especially high-fat varieties.

To supplement DHA and EPA, which fish are worth eating more?

Based on comprehensive considerations, here are some common fish varieties that are also rich in DHA and EPA while avoiding high-mercury fish:

Salmon has the highest content of DHA and EPA. Eating 20g a day can meet the human body's needs, but the price is relatively high. Sea bass is the most suitable high-fat fish variety among freshwater fish. Hairtail and tuna are affordable choices among marine fish.

Fish is delicious, but don’t drink too much

When talking about fatty fish, it is undeniable that they are often rich in EPA and DHA, two polyunsaturated fatty acids that are recognized as "health friends." Compared with red meat rich in saturated fatty acids, choosing to consume high-fat fish is more beneficial to health .

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

However, it is important to keep in mind that excessive intake of any type of fatty acid can cause health problems . China's dietary guidelines recommend consuming 40 to 75 grams of fish per day. As long as your meat intake is within normal standards, eating high-fat fish in moderation should be a safe choice.

In addition to EPA and DHA, eating fish in moderation can also supplement protein, vitamin B (especially B12), and vitamin D.

Two principles to avoid high-mercury fish

When consuming fish, people often worry about environmental contamination, especially that fish may be high in heavy metals, such as mercury. To avoid these issues, there are two key principles:

1. Herbivorous fish is the first choice, carnivorous fish is the second choice

2. Choose small fish over large fish

At the same time, you can refer to the recommendations of the U.S. Food and Drug Administration (FDA).

Fish from the "best feeding" area can be eaten 2 to 3 servings per week, fish from the "good feeding" area can be eaten 1 serving per week, and fish from the "avoid feeding" area should be avoided as much as possible.

Image source: Nutritionist Gu Zhongyi

Fish to avoid include shark, bigeye tuna, mackerel, marlin, swordfish, kingfish, and tilefish.

These guidelines can help you reduce the risk of mercury intake while still enjoying great food.

When cooking fish, avoid frying

Fried fish

Although frying fish is delicious, it is not a recommended way of cooking it .

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

Studies have shown that frying can cause a serious loss of omega-3 fatty acids in fish, including EPA and DHA[10]. Under high temperatures, polyunsaturated fatty acids in fish will oxidize, producing harmful substances and may even generate trans fatty acids .

In addition, the high calorie content makes the benefits of fried fish almost negligible .

Don't eat salted fish

Several studies have shown that nitrosamines in salted fish are associated with an increased risk of cancer, especially gastric and esophageal cancer. Chinese salted fish (pickled products) and moldy foods have been classified as Class 1 carcinogens by the International Agency for Research on Cancer (IARC) .

Grilled fish

Relatively speaking, studies have shown that grilling fish can better preserve its vitamins, minerals, EPA and DHA.

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

However, it should be noted that the grilled fish here does not refer to the traditional Chongqing grilled fish, but refers to a low-temperature baking method without adding oil.

Steaming

Steaming is considered the healthiest way to cook fish .

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

Very little oil is used during the steaming process, which can better preserve the umami flavor of the fish. At the same time, nutrients such as EPA and DHA can also be preserved, unlike the boiling method which will cause the loss of water-soluble nutrients.

Even when steaming, research shows that cooking for more than 30 minutes can lead to a decrease in EPA and DHA content .[11]

Key points

References

[1] Luo Yongkang. Analysis of fatty acid composition of muscle and viscera of seven freshwater fish species [J]. Journal of China Agricultural University, 2001(04):108-111.

[2] Han Yingxue, Lin Wanling, Yang Shaoling, Li Laihao, Huang Hui, Yang Xianqing, Wang Jinxu, Wu Yanyan, Zhai Honglei, Hao Shuxian. Analysis of muscle fat content and fatty acid composition of 15 freshwater fish species[J]. Food Industry Science and Technology, 2018, 39(20): 217-222

[3] Zu Liya, Luo Junxiong, Fan Tie. Comparison of EPA and DHA content in marine fish and freshwater fish fat[J]. China Oils and Fats, 2003(11):48-50.

[4] Liu Sha, Deng Fangming. Research progress on EPA and DHA content and enrichment methods in freshwater aquatic products[J]. Grain and Oils, 2009(06):4-6.

[5] Huang Rui, Chen Shaowei, Chen Zihui, Peng Jiewen, Wang Ping, Huo Weilun, Huang Weixiong, Yang Xingfen. Risk-benefit assessment of polyunsaturated fatty acids in common marine fish in coastal Guangdong Province and their co-intake with methylmercury on neurodevelopment[J]. Chinese Journal of Food Hygiene, 2019, 31(03): 199-204.

[6] Ding Haiyan, Sun Xiaojie, Sheng Xiaofeng, Zhao Yanfang, Shang Derong, Zhai Yuxiu. Nutritional composition and comparative analysis of muscle of several major aquaculture freshwater and marine economic fishes[J]. Food Science and Technology, 2016, 41(03): 150-155.

[7] Zhang Dongmei, Yu Luli, Wang Yuehui. New nutritional evaluation of EPA and DHA in silver carp fatty acids [J]. Fisheries Science and Technology Information, 1997(05):1-4.

[8] USDA Food Composition Database

[9] Chinese Food Composition Table Standard Edition 6

[10] Liu Qiongxia, Lin Xiuwen, Ji Wei, Xie Jie, Liang Yue, Feng Lina. Effects of household cooking methods on the nutritional value of fish[J]. Food Safety Guide, 2019(06):161.

[11] Yang Huicheng, Lan Mengzhe, Lin Rouling, Wu Xiaotong, Yuan Lang, Zhong Hanshi, Wei Xiaoqun. Effect of cooking time on fatty acids in fish[J]. Journal of Food Safety and Quality, 2019, 10(18): 6233-6240.

Author: Gu Zhongyi, Director of Beijing Nutritionist Association

Review | Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center