Salmon has long been an obvious menu choice for the health conscious, since it contains proteins, vitamins and fatty acids that are linked to better health. But a new study out today muddies the reputation of the popular fish's farmed version.
In research that analyzed approximately 700 farmed and wild salmon, scientists showed farmed salmon contains significantly higher levels than in wild salmon of contaminants like PCBs and dioxins.
The level of toxins was high enough that the authors warned eating more than one serving of farmed salmon a month could slightly increase the risk of getting cancer later in life. Toxicologists from the Food and Drug Administration, however, say that warning was overstated.
Not All Regions Face Same Fish Flaws
Some regions produced more contaminated fish than others, according to the research. The highest levels were found in salmon farmed in northern Europe — the authors advised eating no more than a quarter of a serving of these fish every month.
Farms in Canada and Maine produce slightly cleaner fish so a half a serving every month was deemed acceptable, while eating a whole monthly serving of farmed salmon from the least contaminated farms in Chile or Washington state was considered safe.
"There is good evidence that intake of salmon fats is healthy," said David Carpenter of the Institute for Health and the Environment in Albany, N.Y., and coauthor of the study that appeared in the journal, Science. "But when you add the carcinogenic contaminants, you also put yourself at risk."
To test the fish and set their recommendations, the authors used standards and advisories outlined by the Environmental Protection Agency. EPA advisories define risk as one cancer case per 100,000 people.
But while few have challenged the team's findings, some, including representatives from the FDA and the salmon farming industry, take issue with their advice to consumers.
"We've looked at all the data and our advice to consumers is not to alter their consumption of farmed or wild salmon," said Terry Troxell, director of the FDA Center for Food Safety and Nutrition.
Troxell points out the recent tests were performed on raw salmon and included their skins. One way to reduce the amount of possible toxins in a salmon serving is to cook the fish and remove the skin. Even with the skin, Troxell says consumers should not worry.
"Salmon is an excellent source of Omega 3 fatty acids, vitamins and proteins," he said. "These [contaminant] levels are extremely low and are not of public health concern to us."
A Heart-Healthy, Popular Fish
The new findings could confuse a lot of people. Salmon is the third-most-popular type of seafood in the country, after canned tuna and shrimp. Americans eat more than 207,000 metric tons of the fish every year.
The emergence of salmon farms over the last two decades have made the fish more affordable, and fish from these farms make up most of the salmon that is eaten (more than 58 percent), according to United Nations figures.
Part of the popularity of the fish lies in its reputation as a healthy food. The American Heart Association has recommended people eat two servings every week of fatty fish, such as salmon or tuna, in order to get their doses of Omega 3 fatty acids, which have been shown to promote heart health.
"The nutritional benefits of salmon are pretty amazing," said Charles Santerre, a professor of food and nutrition at Purdue University in West Lafayette, Ind., and a consultant for the salmon farm industry. "I strongly believe that all the data we have today suggests that everyone should be eating more farmed salmon."
The problem is the very fish fat that's believed to be good for you can become a depository for pollutants from surrounding water and feed. Chemicals such as PCB and dioxins were once widely used. They have long since been banned, but not before they began to permeate fields and oceans.
Fish pick up the pollutants from the waters around them and from the food they eat. Farmed salmon generally pick up higher amounts because they eat feed manufactured from ground-up junk fish — small fish captured by fishing vessels with no commercial value on their own. The concentrated feed is rich in oils and proteins, but also in pollutants. These chemicals end up in the fatty tissue of the salmon.
High levels of the pollutants are believed to increase the risk of some cancers and, in pregnant or breast-feeding women, harm the developing brains of fetuses and infants.
While a number of smaller studies in the past have suggested similar results, the scope of this research, which was funded by the Pew Charitable Trusts, has led at least one expert, Robert Lawrence, a professor at Johns Hopkins University's School of Health, to become more cautious.
"There's no doubt that fish is good for you," said Lawrence. "But these data suggest if you're going to eat farmed salmon then eating it a little less frequently would be a good idea."
Soy Feed: a Solution?
But Alex Trent, director of Salmon of the Americas, a Princeton, N.J.-based organization of 80 salmon farmers in the United States, Canada and Chile, argues contaminant levels in farmed salmon are minimal and dropping.
Salmon farms have been trying to reduce the amount of toxins in their farmed fish by adding pollution-free vegetable products to salmon feed, such as soy and canola oil. Trent says most feed fed to farmed salmon in the country is now 30 percent to 50 percent soy or canola oil-based.
"We've got levels down to a little over 1 percent," he said of contaminant levels in the fish. "We're not patting ourselves on the back and saying that's great. PCBs don't belong in food. We're working on getting those numbers to be even lower."
In the meantime, Eric Rimm of the Harvard School of Public Health in Cambridge, Mass., points out numbers alone may suggest farmed salmon's benefits still outweigh any risk. One in two Americans die every year from cardiovascular disease, while the risk of developing cancer from contaminants remains uncertain and undocumented.