Fish is an important part of a healthy diet. It is rich in protein, omega-3 fatty acids and other essential nutrients, and low in unhealthy saturated fats.
Experts recommend eating two to three servings of fish a week. However, keep in mind that some types may contain high levels of mercury.
Health Hazards of Mercury
Mercury is a natural element that can be released into the environment through natural processes (volcanic eruptions and forest fires) or through human activity (burning coal, oil, or wood for fuel). When a substance is transported through the air, it can fall to the ground in the form of raindrops, snowflakes, dust, or gravity, contaminating soil or water.
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When mercury ends up in lakes, oceans, and rivers, it undergoes a process known as methylation, in which certain microorganisms in the water convert mercury compounds into the form of methylmercury. It is absorbed through the gills and also accumulates when the fish eats small fish. As you move up the food chain, this natural element becomes more concentrated in the animal’s body.
Consumption of high doses of mercury in humans can cause serious health problems, especially affecting the brain and nervous system, including:
tingling or numbness in the mouth, hands, or feet; blurred vision and hearing; loss of peripheral vision; muscle weakness and inability to coordinate movements.
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In pregnant and breastfeeding women, mercury exposure can also affect the development of the baby’s brain and nervous system. It can also cause disturbances in your baby’s cognitive thinking, memory, attention, speech, fine motor skills, and visual-spatial skills.
Fish high in mercury
Mercury levels vary between different species of fish. This is due to factors such as the type of vertebrate, its size, location, habitat, diet and age.
Predatory fish (which feed on other smaller fish) are larger and are at the top of the food chain, so they tend to store more of this element, which is dangerous for humans.
nutritionist, sports nutritionist, nephrologist at the Hadassah Clinic branch
“However, the main source of heavy metals and carcinogens for humans is not food, but tobacco and the environmental situation (e.g. exhaust gases).”
Fish that contain higher levels of mercury include:
shark; marlin; swordfish; mackerel; Atlantic bighead; bigeye tuna.
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The American Food Control Agency issued recommendations where it divided fish into three categories and, depending on the category, indicated the possible frequency of its consumption.
For example, the “best choice” column includes anchovies, mackerel, sea bass, herring, all types of small fish, salmon, sardines, squid, crabs, etc. These types can be safely consumed two to three times a week.
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The next column, “good choices” (or “caution, may contain mercury”) includes carp, Chilean sea bass, bluefish, snapper (emperor fish), albacore and yellow tuna. It is recommended to eat this type of fish no more than once a week.
And the third group are fish that should be avoided. We have already listed their types above.
How is mercury controlled?
The content of metals, including mercury, in the food industry is controlled at different levels (technical regulations on food industry safety). For different fish, sanitary requirements and uniform technical regulations establish certain limits of the permissible norm, and they depend on the ability of the fish to accumulate it.
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For example, for sprat there will be very low figures, no more than 0.5 mg/kg, and for tuna the threshold is higher, since the longer the fish lives, the more mercury it accumulates. Therefore, in tuna the permissible limit of mercury reaches 1 mg/kg (double that for other species).
But there are also more “fickle” fish, for example shark, swordfish, marlin, mackerel and big-eyed tuna. They can accumulate up to 5 mg of mercury.
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