Salmon at 75 on Liberty Wharf. Boston Globe Staff/Photographer Jonathan Wiggs
A new study grabbing headlines links a high intake of fatty fish with a modestly reduced risk of breast cancer.
I’m always hesistant to report on diet and cancer prevention studies because it’s very tough to single out a particular food from a person’s diet and conclude that it altered cancer risk.
Fortunately, foods usually associated with cancer prevention—such as colorful fruits and vegetables—are usually nutritious while those associated with a higher cancer risk—such as hot dogs and deli meats—usually aren’t.
Such is the case with the latest finding published in the British Medical Journal linking a high intake of oily fish rich in Omega-3 fats with an 18 percent lower risk of breast cancer. These types of fish, such as salmon, also have been associated with heart benefits, so it doesn’t hurt to eat more of them.
In the latest finding, Chinese researchers reviewed 26 previous studies involving nearly 900,000 women that either examined their fish intake, overall intake of Omega-3 fats from fish and plant oils, or measured concentrations of Omega-3 fats in body tissues.
The researchers found that those who reported eating the most Omega-3 fats in fish or who had the highest concentration of these fats in their body were the least likely to have been diagnosed with breast cancer. Each 0.1 gram daily dose of Omega-3 fats was associated with a 5 percent lower breast cancer risk with the benefits leveling off at about 0.3 to 0.4 grams per day.
What’s perhaps just as telling, though, are the links the researchers didn’t find: Omega-3 fats from plant sources like flax seeds and walnuts weren’t associated with a reduced breast cancer risk; nor did the overall intake of fish—many of which have scant amounts of Omega-3 fats—make a difference.
The National Library of Medicine states on its website that “fish rich in omega-3 fatty acids include mackerel, tuna, salmon, sturgeon, mullet, bluefish, anchovy, sardines, herring, trout, and menhaden.” Smaller fish like salmon, herring, and sardines, though, tend to contain more than larger fish like tuna. It’s also hard to know how much Omega-3 fats are in the fillet you buy at the supermarket since the amount largely depends on the fish’s diet.
Some research suggests wild Pacific Salmon contain far more Omega-3 fats than farmed varieties of salmon. But a 2008 study that sampled fish in grocery stores around the country found that farmed Atlantic salmon and trout had adequate amounts of Omega-3 fats while farmed tilapia and catfish had little to none.
While the researchers found that some wild fish salmon contain as much as 4 grams of Omega-3 fats per 3.5-ounce serving, most varieties typically contain about 1 gram.
That means women should eat about three servings a week to maximize the potential breast cancer prevention benefits.