Recent research has linked sushi to an increased risk of cardiovascular disease.
This warning comes from a study published in the Journal of Risk Research. This is not good news! But how can anti-inflammatory, so good for you salmon, mackerel and tuna (commonly found in sushi) cause such a warning? Salmon, mackerel and the fatty tuna found in sushi both contain a healthy amount of omega-3 essential fatty acids (EFA), which we know to be anti-inflammatory and good for heart health.
The reason for the warning is the mercury – which can be found in high amounts in the tuna and mackerel used in sushi.
This environmental toxin has built up to alarming levels in certain fish, to such an extent that the harm from the toxin outweighs all health benefits. Traces of mercury, largely in the form of methylmercury, can be found in nearly all fish species, although the levels are higher in some fish than in others. Fish bioaccumulate methylmercury in their muscle tissues primarily as a result of eating plants and other organisms that contain methylmercury. Methylmercury then biomagnifies through the food chain when predators, such as other fish, eat organisms that have already bioaccumulated methylmercury in their muscle tissues. Over time top predators will have greater tissue concentrations of methylmercury than either their prey or the surrounding environment. Shark and swordfish are examples of fish that are high in the food chain and contain high concentrations of methylmercury.
As well as shark and swordfish other fish that have accumulated higher levels of mercury include certain species of tuna (Ahi, yellowfin, bigeye and albacore including canned), bluefish, mackerel (king, Spanish, gulf), and Chilean seabass. Note that Chilean seabass, shark and swordfish should also be avoided because they are overfished. The not as expensive skipjack or light tuna does not contain as much mercury but unfortunately it also does not contain a significant amount of Omega-3 fatty acids.
A feast of sushi can contain contaminated tuna, mackerel and cod (Alaskan cod is a medium source of mercury).
How to safely get your Omega-3 EFA from fish? Salmon, sardines, anchovies, herring, mackerel (N Atlantic, chub), and freshwater trout are all low in mercury and a good source of Omega-3 EFA. Other safe fish to eat are Arctic cod, catfish, haddock, perch, sole, tilapia and shellfish (although they do not provide Omega- 3 EFA). To reduce your exposure to other contaminants such as antibiotics chose organic fish whenever possible.
For a guideline regarding fish with higher concentrations of mercury, Health Canada recommends that one consumes no more than 150g per week with the exception of women who are or may become pregnant and breastfeeding mothers who should consume no more than 150 g per month. For children 5 – 11 years of age up to 125 g per month. Very young children between 1 and 4 years of age no more than 75 g per month. Separate advice is given for canned albacore (white) tuna. Women who are or may become pregnant and breastfeeding mothers may consume up to 300 g a week of albacore tuna (approximately 2 cans of tuna a week). Children 5 – 11 years of age approximately 1 can a week and children 1 – 4 years of age approximately ½ can per week. There are no restrictions around skipjack or light tuna.
So think about the fish that you are eating, and the next time you have sushi you may need to expand your repertoire!