A STUDY by American scientists has sparked new fears over the safety of Scottish farmed salmon by warning people that they should eat no more than two portions a year.
Researchers at the University at Albany, part of New York State University, concluded that the health benefits of eating Scottish fish are outweighed by risks caused by pollutants.
Where the salmon comes from and what the fish is fed determine whether the health risks will outweigh the benefits, according to the study published in the Journal of Nutrition recently.
Researchers found that the contaminant levels in farmed salmon from certain regions of the world increased the risk of cancer enough to outweigh its coronary health benefits. The toxin levels were so high in some farmed salmon from Europe that people could not afford to eat more than a single serving every five months, they said.
David Carpenter, lead author of the study and director of the Institute for Health and the Environment at the state University at Albany's School of Public Health says
although the toxin levels in wild salmon weren't high enough to exceed the health benefits, the same was not true for farmed salmon, which are raised on a diet of fish oil.
The level of contaminants in fish oil - often derived from local fish - vary depending on the region of the world.
Farmed salmon from South America had the lowest level of pollutants followed by farmed salmon from North America. Salmon from Europe had the highest level of pollutants, according to the study. "We think it's because that area's been industrialized much longer," Carpenter said.
After other studies indicated that fish oil increases the levels of toxins in farm-raised salmon, some fish farmers in recent years have switched to vegetable oil pellets.
But a study last year found the heart-health benefits from fish like salmon were weakened when they were fed vegetable oil instead of fish oil.
To determine whether the heart-health benefits of farmed salmon were worth the risk, researchers used advisories developed by the U.S. Environmental Protection Agency for cancer effects and the fish consumption advisory issued by the American Heart Association.
"In farmed salmon, the cancer risk dominated the health benefits," Carpenter said. "We're not opposed to farmed salmon, just how it's farmed. The industry can reduce the level of toxins by changing how they feed the salmon'.
That's not a call for people to shun farmed salmon, however. Salmon and other fatty fishes like mackerel and sardines are rich in omega-3 fatty acids, the healthy fat that scientists say raises the "good" HDL cholesterol and lowers the "bad" triglycerides. The AHA recommends people eat fish - particularly fatty fishes - at least twice a week.
Recent studies from Scotland have reported that feeding salmon vegetable oils except in the final stages of farming resulted in salmon with significantly lower levels of contaminants but with most of the omega-3 fatty acids obtained from the standard diet.
'The benefits exceed the risks for wild Pacific salmon, but the risks exceed the benefits for farmed Atlantic salmon as a group. The risks are greatest in Scotland, the Faroes and Norway,' says the report.
'Omega-3 fatty acids can be consumed in many forms of seafood, including wild salmon, farm-raised salmon from Chile (which were found to contain the lowest concentrations of pollutants in farm-raised populations), and in some oils, nuts and vegetables.'