Cadmium, mercury and lead: what is the danger of eating predatory fish?
The World Health Organization (WHO) recommends eating fish at least twice a week. This product is a leader in the content of omega—3 polyunsaturated fatty acids, calcium, phosphorus, B vitamins and other essential substances. However, fish can also be harmful to the body if it contains heavy metals, is riddled with parasites, or causes a severe allergic reaction. How mercury and lead accumulate in tuna and shark, is pescetarianism harmful to health, and who should completely abandon fish dishes? — in the Izvestia article.
Who can't
It's really better for some people not to eat fish at all, says Natalia Nikitina, a therapist at the Be Healthy clinic in St. Petersburg.
"First of all, these are patients with confirmed severe allergies to fish (especially to parvalbumin, the main allergen of white fish) or seafood," says Nikitina. — The reaction can be very serious, up to anaphylaxis.
It is also necessary to abstain from fish in very rare cases of specific metabolic disorders, which are detected individually, at a doctor's appointment. In limited quantities and with great care, the therapist advises including some fish dishes in the diet for pregnant and lactating women, as well as for children (especially younger ones).
— There is no absolute ban on any particular type of fish from the point of view of evidence-based medicine, if the fish is of high quality and properly cooked, — comments Natalia Nikitina. — However, there are species whose consumption should be limited or excluded as much as possible due to the high potential health risk.
Large marine predators such as tuna, shark, and swordfish are prone to accumulating toxic substances, including mercury, cadmium, and lead, warns Igor Glamazdin, Doctor of Veterinary Sciences, Director of the Institute of Veterinary Medicine, Veterinary and Sanitary Expertise, and Agro-Safety at ROSBIOTECH University. This is due to their long life cycle and position at the top of the food chain.
"By absorbing small fish and plankton, they accumulate pollutants present in the marine environment," explains the scientist. — The World Health Organization recommends limiting the consumption of these types of fish to 1-2 servings per week (100 g each). It is advisable for pregnant women, nursing mothers and young children to completely exclude them from the diet.
The therapist emphasizes that mercury (methylmercury) is a neurotoxin that can harm the developing nervous system of the fetus and child. It is worth choosing species with a low mercury content — wild salmon or salmon grown on responsible farms, sardines, herring, pollock, cod. And limit yourself to 1-2 servings per week.
If it is impossible to abandon predators for some reason, then the scientist recommends taking precautions.
— Choose young individuals in which the mercury concentration is lower; remove the skin and subcutaneous fat in which toxins accumulate. Use gentle cooking methods (steaming, baking); however, broth should not be eaten, as heavy metals can pass into it," comments Igor Glamazdin.
According to the scientist, mercury is found in various types of mackerel, but Atlantic mackerel is considered safe in terms of its content and is suitable for regular consumption.
—King mackerel (Scomberomorus cavalla) is a species with a high level of mercury accumulation, comparable to tuna," Glamazdin continues. — Thus, when choosing mackerel, preference should be given to the Atlantic type and the consumption of king mackerel should be limited.
Due to the risk of parasites, in particular listeria, entering the body, experts advise to refrain from dishes made from raw fish (sushi, sashimi). Such products should not be in the diet of babies, as well as women during pregnancy and breastfeeding.
Special attention should be paid to fish caught independently and cooked in field conditions. Proper cooking is important because it is not always clear what kind of "surprise" lurks in the fish.
— Crucian carp, carp and ide are often infected with Opisthorchis felineus (feline fluke), the causative agent of opisthorchiasis. The parasite affects the liver, gall bladder and pancreas, causing chronic inflammatory processes, — continues Igor Glamazdin.
According to the scientist, pike, perch and burbot may be carriers of broad tapeworm (Diphyllobothrium latum), the causative agent of diphyllobothriasis, a disease that affects the intestines and disrupts the absorption of vitamin B12.
"Cod, haddock, herring, and mackerel in their raw form may contain larvae of Anisakis simplex, which cause anisakidosis, a parasitic disease with allergic and gastrointestinal manifestations," comments Igor Glamazdin.
As preventive measures, the scientist recommends heat treatment — cooking and frying for at least 20 minutes at temperatures above +60 ° C; deep freezing at -20 ° C for at least 48 hours; thorough cleaning and removal of internal organs before cooking. But it is better to refrain from eating raw and lightly salted fish (for example, homemade stroganina or sushi from freshwater fish).
Anchovies and gout
For patients with gout and hyperuricemia (elevated uric acid levels), the therapist advises limiting the consumption of certain types of fish products. Anchovies, herring, mackerel, sardines, and caviar are undesirable, as such products can provoke seizures.
Patients with severe kidney diseases are at risk: Natalia Nikitina emphasizes that they need to control the total protein and phosphorus in the diet, so the amount of fish (as well as other protein products) should be regulated individually by a doctor or nutritionist.
— Fatty fish, as well as smoked, salted and fried fish, can worsen the condition of people with chronic gastrointestinal diseases in the acute stage (gastritis, pancreatitis, cholecystitis), warns Natalia Nikitina. — During an exacerbation, doctors often recommend temporarily eliminating such foods or eating only low-fat varieties (cod, pollock, walleye) boiled or steamed. They should be eaten in small quantities, observing the reaction.
For people with established hypersensitivity to histamine, the therapist recommends avoiding fish, which easily deteriorates and accumulates histamine. These are tuna, mackerel, and herring, especially if they are not fresh or have been frozen for a long time. Such food can provoke a pseudoallergic reaction.
Tilapia is a popular white fish with a high protein content (about 26 grams per 100 grams) and low calorie content. It is acceptable in the diet, but it should not be the main source of omega-3 fatty acids, the professor emphasizes.
—The biochemical composition of tilapia is characterized by a low content of omega-3 polyunsaturated fatty acids and an increased level of omega-6, an excess of which can contribute to inflammatory processes," says Igor Glamazdin.
The scientist advises to take into account the sanitary risks of tilapia, as well as pangasius and catfish. These species are omnivorous and, when grown in unfavorable conditions (especially on Asian farms), may contain antibiotics, growth hormones, and toxins from polluted water.
—Individuals caught in the wild also pose a potential threat in terms of parasitic and microbiological risks," the scientist continues. — Recommendations: purchase fish only from certified suppliers; thoroughly rinse and undergo intensive heat treatment (frying, baking). If in doubt, give preference to safer alternatives: cod, pollock, trout.
A fish that needs to be treated with extreme caution
The most useful
The professor considers herring, mackerel and sardines to be the most useful types of fish — they are rich in omega-3 fatty acids and vitamin D, contribute to the normalization of the lipid profile and maintain immune function.
— Salmon (wild and well-grown) is valued for its high protein content and polyunsaturated fatty acids. Cod and pollock are low—calorie varieties with a high iodine content, they are suitable for dietary and preventive nutrition. Trout contains fewer pollutants than salmon and is characterized by a high level of beneficial lipids. Flounder and halibut are easily digested and are well suited for people with digestive disorders and at the rehabilitation stage,— says Igor Glamazdin.
The therapist recommends combining fish with vegetables — fresh, stewed, baked, grilled.
— Any non-starchy vegetables (cabbage of all kinds, zucchini, eggplant, asparagus, string beans, tomatoes, cucumbers, leafy greens, onions, garlic) and starchy (carrots, pumpkin) are suitable. Fiber improves digestion and absorption of nutrients from fish (for example, fat—soluble vitamins), explains Natalia Nikitina.
Win—win options for the side dish are brown rice, quinoa, buckwheat, bulgur. They provide a person with complex carbohydrates and fiber, the dish turns out to be balanced. Potatoes (preferably baked or boiled): a classic and satisfying combination.
— Parsley, dill, coriander, basil, rosemary, thyme not only improve the taste, but also have antioxidant properties. And lemon juice improves the taste of the dish, promotes the absorption of iron, the therapist suggests.
In moderation, you can add foods containing healthy fats to fish — avocados, nuts, seeds (flax, chia, pumpkin). They enrich the dish with omega-3 if the fish is low-fat.
But fatty milk sauces and cheeses (especially in large quantities) are not recommended to be combined with fish.
— Excess calories and saturated fats can offset the benefits of fish oils (omega-3). In theory, calcium from dairy products may slightly interfere with the absorption of iron from fish, but in practice this is rarely critical with a balanced diet, says Natalia Nikitina.
Other sources of saturated fats (fatty meat, butter in large quantities) also increase the total calorie content and load of saturated fats.
— Legumes (beans, peas, lentils) are useful in themselves, but in combination with fish they can put an excessive load on the gastrointestinal tract in some people (bloating, gas formation), — the therapist continues. — Strong alcohol loads the liver, which is already busy processing proteins and fats from fish. At the same time, the absorption of useful substances may worsen. Dry white wine in small quantities is considered a more acceptable classic combination.
Instead of meat
A diet in which meat is completely excluded from the diet and only fish is eaten is called "pescetarianism." According to Natalia Nikitina, it can be quite healthy and balanced, but only with a very thoughtful approach. The advantages are that fish is an excellent source of omega-3 (especially fatty marine fish). This is the key to supporting the heart, blood vessels, brain, and combating inflammatory processes. The fish protein is of very high quality, the product contains all the essential amino acids, and is easier to digest compared to the same red meat.
Fish is also rich in vitamins and minerals such as vitamin D (fatty fish), B12, iodine, selenium, zinc and others. With proper diet planning, one can observe a reduction in the risk of cardiovascular diseases compared to a diet rich in red meat, the doctor admits. But such a diet has its own nuances.
— However, it is important to pay attention to the risks associated with pescetarianism. In particular, it is a deficiency of heme iron, which is important for the body," says the interlocutor of the publication. — Iron from fish (non-heme) is absorbed worse than from red meat (heme).
The doctor strongly recommends that fish lovers include other sources of non-heme iron in their diet (legumes, lentils, tofu, spinach, fortified cereals), necessarily combining them with vitamin C (citrus fruits, bell peppers, broccoli) to improve absorption. At the same time, it is necessary to monitor the level of ferritin by analysis.
Another danger is that you can "earn" vitamin B12 deficiency on a fish diet.:
— Although fish contains B12, with strict pescetarianism and the exclusion of eggs and dairy products, there is a risk of deficiency. It is important to make sure that there are enough fatty fish, shellfish (they are very rich in B12), eggs and/or dairy products in the diet. If necessary, according to the doctor's prescription, you will need to buy fortified foods or special supplements," the therapist comments.
Natalia Nikitina also advises careful selection of fish, excluding species with high mercury content or caught in polluted reservoirs.
— If you only eat low-fat fish or overdo it with frying on unhealthy oils, then an imbalance of fatty acids is possible: omega—3 sources (fatty fish, flaxseed or ginger oil, chia or flax seeds, walnuts) will help to correct the situation, - comments Nikitina.
A fish diet is fraught with a possible zinc deficiency, because it is absorbed worse from fish than from meat. But seafood such as oysters and crab meat are leaders in the content of this trace element. If you can't afford such delicacies, then you can supplement your diet with nuts, seeds, legumes, and whole grains.
When switching only to fish, the therapist advises you to consult a nutritionist to create a competent nutrition plan. Without taking into account the various nuances of the diet, it can lead to problems.
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