Eating fish not only nourishes the brain, but it also offers numerous benefits for the human body due to its rich protein, vitamins, and fish oil content. However, it is important to be aware of potential risks as well. According to nutritionist Xia Ziwen, large fish like tuna and swordfish, which occupy higher levels in the food chain, contain higher amounts of mercury. Excessive consumption of these fish types may have implications on cognitive abilities.

Nutritionist Xia Ziwen points out that different types of fish have varying nutrient profiles. For example, tuna not only has rich protein content but also contains Omega-3 fatty acids, vitamins, and minerals. However, it is important to note that the higher a fish is in the food chain, the higher the accumulation of heavy metals such as methylmercury. Therefore, large fish like tuna, swordfish, mackerel, and shark, which are at the top of the food chain, have higher levels of mercury compared to smaller fish. It is advisable to avoid excessive consumption of these fish.

Xia Ziwen provides an example using the maximum level of methylmercury in fish meat, which is at 1ppm. A 50 kg adult should not consume more than 65 grams of such fish per week, equivalent to approximately 2 servings of protein. Additionally, fish skin, internal organs, and fat tend to accumulate heavy metals, so their intake should be reduced to minimize the risk of methylmercury residue in the body.

When methylmercury is ingested through food and absorbed by the gastrointestinal tract, the absorption rate can exceed 95%. This can affect brain development in fetuses and potentially impact cognitive abilities. Xia Ziwen advises pregnant women and children under 6 years old to avoid consuming large fish, while adults should also limit their intake.

When consuming fish, it is advisable to choose smaller species with relatively lower levels of heavy metal contamination, such as salmon, mackerel, sardines, sauries, catfish, and perch. The size of the fish can be approximately gauged by making a circle with the thumb and middle finger around the fish belly. This size of fish is generally considered a better choice. Additionally, it is important to vary fish species consumed to avoid eating the same type frequently, thus reducing the overall burden of exposure.