Finding omega-3 fats in fish: Farmed versus wild

Recently, a Harvard Heart Lettersubscriber emailed us a question: Is there a difference between farm-raised and wild-caught salmon in terms of omega-3 fatty acid content?

I've wondered about this myself while standing at the fish counter at my local grocery store. I can often find farm-raised Atlantic salmon for about $6.99 a pound, while the wild-caught salmon may be nearly twice as expensive. Salmon and other fatty fish are the main dietary source for omega-3 fatty acids, which are known to lower the risk of heart disease.

It turns out that you probably won't shortchange your heart if you choose the less-costly farmed salmon, as both types seem to provide similar amounts of omega-3s per serving. But that's likely because farm-raised salmon tend to have more total fat — and therefore more omega-3 fat — than wild ones.

How the total fat content of salmon measures up

As Dr. Bruce Bistrian, professor of medicine at Harvard Medical School, explained to me, fish are what they eat. "In the wild, salmon eat smaller fish that are high in EPA and DHA — the beneficial, long-chain omega-3 fatty acids." Farm-raised salmon eat high-protein food pellets. While location and environmental changes can affect the diet of a wild salmon, the flesh of a farmed fish reflects the farmer's choice of pellets. In particular, farmers often feed the young salmon pellets made from plant and animal sources, then add the more expensive fish- and fish-oil–enriched pellets later in the fish's lifespan.

A study that measured fatty acids in 76 different fish species from six regions of the United States found big variations in the omega-3 content in the five different salmon species tested — especially the two farm-raised varieties. The omega-3 content ranged from 717 milligrams (mg) to 1,533 mg per 100 grams of fish (equal to a "standard" 3.5-ounce serving). Compared to the wild-caught varieties, farmed fish tended to have higher levels of omega-3s, but they also contained higher levels of saturated and polyunsaturated fats. But the amount of saturated fat isn't alarming. For comparison, a serving has about 1.6 grams, which is about half as much in the same amount of flank steak.

The best choices for salmon — and the rest of your plate

Bottom line: Don't stress too much about your salmon selection. Follow the American Heart Association's advice to eat two servings of fish a week, letting affordability and availability guide your choices. As for me, I often opt for farmed salmon for dinner once a week or so, but I'll splurge on wild salmon if it looks especially good. When I have canned tuna, I look for the "chunk light" variety, which is lower in mercury than other varieties. (For more on that topic, see one of my previous blogs). Other good fatty fish choices include sardines, herring, bluefish, and mackerel.

And don't forget to keep the big picture in mind when choosing what to eat. Nutrition experts like Dr. Bistrian stress that much of the most compelling evidence about a heart-healthy eating patterns comes from studies of the Mediterranean diet, which includes fish as well as lots of fruits and vegetables, whole grains, nuts and olive oil but minimal amounts of meat and dairy. "If you eat more fish in the context of other changes in your diet, that's more likely to confer a benefit," says Dr. Bistrian.