Tuna is a low calorie fish with high protein content and high nutritional value.In tuna meat, however, there is methylmercury, which is toxic to humans, which is why women who are pregnant and breastfeeding should pay special attention to too much tuna consumption.
Tuna is a large predatory fish that lives in sea areas mainly with warm waters. Different species of tuna live in the Atlantic, Indian and Pacific, and the adjacent seas are less often found in cold waters, such as the North Sea and the Barents Sea.The largest specimens of bluefin tuna fish reach a weight of 700-800 kg and live up to 50 years.On average, tuna weighs up to 200 kg, but there is also a bonito species, whose weight does not exceed 20 kg.Tuna meat is dark in color – from pink to purple.This is the result of a strong blood supply to the muscles and a high content of myoglobin that stores oxygen in the tissues.Thanks to this, the tuna can move very quickly and maintain a high body temperature.
In recent years, tuna fishing is around 4 million tons per year.68 percent of fish come from the Pacific Ocean, 22 percent from Indian, and the remaining 10 percent from the Atlantic Ocean and the Mediterranean.The amount of fish that can be fished in individual periods is regulated so as not to allow overfishing and thus not threaten the extinction of species.Particular attention is paid to overfishing representatives of the largest species – bluefin tuna, which is a valued delicacy in Japan.The most valuable on the market is bluefin tuna, which at auction Tsukiji fish market in Tokyo reaches record prices.In 2013, tuna weighting 221 kg was auctioned for nearly 1.8 million dollars.In Poland, the consumption of tuna is small.The import of this fish in 2014 amounted to 6.7 thousandtone.This is much less than the import of herring (54.7 thousand tonnes), salmon (101.7 thousand tonnes) or cod (35.8 thousand tonnes).
Tuna nutritional value
Tuna is low in calories and at the same time is an excellent source of protein.100 g of fresh fish provide 108 kcal, 23 g of protein and 0.9 g of fat, which in 1/4 constitute the essential unsaturated omega-3 fatty acids EPA and DHA.These fats are very important in the diet, and their shortages favor, among othersweak immunity, high cholesterol and heart disease.Tuna is a good source of vitamin D, affecting bone health, immunity and general well-being.In Poland, from autumn to spring, when the amount of sun is insufficient to produce the right amount of vitamin D in the skin, it should be especially taken care of its supply with diet and supplementation.Tuna is characterized by a very high content of B vitamins – thiamine (29 percent of daily requirement in 100g), niacin (49 percent) and vitamin B6 (45 percent).They are responsible, among othersfor controlling energy processes and the functioning of the nervous system, which is why tuna is often recommended for physically active people.Mineral components present in significant amounts in fresh tuna are selenium (52 percent of daily requirement in 100g), magnesium, phosphorus and potassium.
Studies show that the vast majority of fish contain trace amounts of mercury and other heavy metals toxic to humans, and the most of this element is accumulated in the meat of butterfish, tuna, perch, eel and swordfish.Tuna is one of the most mercury-containing fish, because it is a predatory species that is almost at the end of the food chain, reaches a very large size and lives up to several dozen years.Mercury is accumulated in fish in the form of methylmercury, which is very easily absorbed from the gastrointestinal tract, penetrates the blood-brain barrier and damages the nervous system.Methylmercury also penetrates the blood-placenta barrier and into the milk of nursing mothers, which is a high risk of malformation of the fetus and infant.Therefore, carefully choose fish and buy only from a reliable source.
A safe amount of tuna in the diet is two 100-gram portions a week.
Acceptable levels of mercury in fish are set at 0.5-1.0 mg / kg of fresh weight and the art allowed for sale must meet these standards, therefore fish consumption should not pose a threat.The average tuna methylmercury contamination is 0.033 mg / kg of fresh weight.However, it should be remembered that fish with a high content of mercury should be consumed in moderate amounts – 1-2 times a week.Pregnant women planning pregnancy and breastfeeding as part of prevention should not consume more than 100 grams of tuna per week, and simultaneous eating of other fish is not recommended.
Watch out for histamine in tuna
For all dark-fish fish, especially canned fish, watch out for histamine.It is a hormone that occurs naturally in the human body, but in excess in sensitive people can trigger strong allergic reactions.Its content is the lowest in fresh fish and grows with storage time.He is responsible for the characteristic smell of a broken fish.International standards set the maximum histamine content at 200 mg / kg of tuna, however, people sensitive to histamine should avoid this fish.
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