NEW YORK (Reuters Health) – While health experts recommend that people eat more fatty fish, the varieties most Americans buy vary widely in their amount of healthy omega-3 fats, a new study suggests.

The American Heart Association (AHA) and other groups recommend that people regularly eat fish, especially fattier varieties such as salmon, trout and mackerel. The goal is to increase consumption of omega-3 polyunsaturated fatty acids, which have been shown to cut triglycerides (a type of blood fat) and have other heart-healthy effects.

But when the researchers on the new study bought a selection of wild and farm-raised fish from supermarkets and wholesalers across the U.S., they found large variations in the concentrations of omega-3 and omega-6 polyunsaturated fatty acids.

In particular, farm-raised trout and Alaskan salmon both had high levels of omega-3 fats and a relatively healthy balance of omega-3 and omega-6 fats, the researchers report in the Journal of the American Dietetic Association.

On the other hand, farm-raised catfish and tilapia had low levels of omega-3 and a much higher proportion of omega-6.

Omega-6 fats, found in sources like soybean and corn oils, are necessary and beneficial. But the typical American diet contains many times more omega-6 fat than omega-3, and such imbalances are thought to promote inflammation in the blood vessels — a key contributor to heart disease.

“Despite recommendations from organizations such as the AHA to increase fish consumption in general, this study shows that not all fish are created equal,” write Dr. Floyd H. Chilton and colleagues at Wake Forest University School of Medicine in Winston-Salem, North Carolina.

“It’s not an issue of farm versus non-farm,” Chilton said in an interview.

Farmed salmon and trout emerged as some of the best choices for people who want to get the potential health benefits of fatty fish, he noted. When it comes to tuna, one of the most popular fish on Americans’ plates, Chilton recommended eating albacore tuna, which has more omega-3 than other varieties.

He and his colleagues arrived at their conclusions after buying 30 species of wild and farmed fish from several U.S. supermarket chains and wholesale distributors, as well as commercial farms in the U.S. and other countries.

They found that the omega-3 content in the fish species ranged from “practically none” to nearly 4,000 milligrams per 100 grams of fish.

When they specifically compared the four most commonly farmed fish — Alaskan salmon, trout, tilapia and catfish — the researchers found that the latter two had much more omega-6 than omega-3 fat. Both species also had high percentages of saturated and monounsaturated fat.

The problem, Chilton and his colleagues say, may be related to the commercial feed given to farmed fish.

Tilapia, they note, is the fastest growing fish in terms of popularity in the U.S., and it is also the most intensively farmed species. They are often given high levels of omega-6 from the vegetable oils used in their feed.

“The message here isn’t that farm fishing in general is bad,” Chilton said. However, he added, there needs to be more awareness of the ways in which farming practices can affect the nutritional content, and potential health effects, of fish.

Last Updated: 2008-07-11 15:40:23 -0400 (Reuters Health)

SOURCE: Journal of the American Dietetic Association, July 2008.