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Omega-3 fatty acids: Does your diet deliver?

Most Americans don’t get the recommended amount of these potentially heart-protecting fats.

Man eating salmon , a good source of heart-protecting omega-3 fatty acides

Recently, a Harvard Heart Letter subscriber emailed us a question about omega-3 fatty acids, the unique fats abundant in many types of fish that may be linked to a lower risk of cardiovascular disease. Is there a difference, he wondered, between farm-raised and wild-caught salmon in terms of omega-3 fatty acid content?

It’s a reasonable question, especially considering that wild salmon is often far more expensive than the farm-raised variety. But how much omega-3 fatty acid do we really need in our diets? And are fish the only source? Here’s a brief summary of what you should know about omega-3s.

Omega-3s and your heart

There are three main forms of these unsaturated fats, which play an essential role in human health (see “Three key omega-3s”). The so-called marine fatty acids, EPA and DHA, have several potential cardiovascular benefits. They might help

  • ease inflammation

  • ensure the heart maintains a steady beat, which may guard against potentially deadly, erratic rhythms

  • prevent the formation of dangerous clots in the bloodstream

  • lower levels of triglycerides, the most common type of fat-carrying particle in the bloodstream.

“Observational studies have shown that the more fish you eat, the lower your risk of coronary artery disease and dying of heart disease,” says Dr. Bruce Bistrian, professor of medicine at Harvard Medical School. These and other data are behind the recommendation both in federal dietary guidelines and from the American Heart Association (AHA) to eat two servings of fatty fish per week. That averages out to about 250 milligrams (mg) of EPA plus DHA a day. Dietary surveys suggest that Americans get less than half that amount.

Farmed vs. wild

If you choose the less-costly farm-raised salmon over the wild-caught, you won’t shortchange your heart. In fact, the farm-raised salmon often contains more DHA and EPA per serving than wild salmon. Still, a 2014 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 mg to 1,533 mg per 100 grams (a 3.5-ounce serving) of fish. Compared with the wild-caught varieties, farmed fish tended to have higher levels of omega-3s, but they also contained more total fat, including some undesirable saturated fat. But the amount isn’t alarming. For comparison, a serving of farm-raised salmon has about 1.6 grams of saturated fat, which is about half as much as in the same amount of flank steak.

In fact, nutrition experts believe that one reason fish-eaters have fewer heart attacks may stem from the fact that they’re eating fish in place of red meat or processed meats like sausage, bacon, or ham, which contain more saturated fat (and in the processed meats, a lot of salt). Both substances are linked to a higher risk of heart disease.

When it comes to selecting fish, the AHA advises people to let affordability and availability guide their choices. Dr. Francine Welty, a cardiologist at Harvard-affiliated Beth Israel Deaconess Medical Center, gives her patients a list of recommended fish choices, which includes albacore tuna, bluefish, herring, mackerel, salmon, and sardines. Canned sardines packed in water are an especially economical choice: they provide 1,300 mg of DHA and EPA per serving and usually cost less than $2 a can. “One of my patients recommends eating them with lemon,” says Dr. Welty.

The fish (and egg) food chain

eggs enriched with omega-3sLike humans, fish get their omega-3s from what they eat. Wild fish eat smaller fish, which feed on algae, the original source of the fatty acids. Farmed fish eat high-protein pellets that may derive from plant, animal, or fish sources, which explains the variability seen in the types of fats found in their flesh.

Similarly, the fats found in egg yolks reflect the hens’ diets, which is why you can find eggs enriched with omega-3s in the supermarket. But check the fine print: although the wording on the carton may say the eggs contain omega-3s, they may contain plant-based ALA rather than DHA and EPA. There’s no good reason to pay a premium price for ALA-enriched eggs, however, as most Americans get plenty of this fatty acid from vegetable oils like soybean and canola oils. Eggs that contain DHA and EPA (courtesy of fish-oil enhanced feed) usually contain around 75 to 100 mg of DHA and EPA per egg, but the amount can vary quite a bit.

Vegetarians: Off the hook?

What about vegetarians, who don’t eat fish (and often don’t eat eggs), and vegans, who avoid all animal-based foods? People who follow these plant-focused diets have lower rates of heart disease than omnivores. Still, some wonder if they should take a supplement containing EPA and DHA derived from algae, just to be sure. But according to Dr. Frank Sacks, professor of cardiovascular disease prevention at the T.H. Chan Harvard School of Public Health, there’s no reason to do so if you eat plenty of ALA-rich foods such as flaxseed, walnuts, pumpkin seeds, and soybean or canola oil. Green vegetables such as Brussels sprouts, spinach, and kale also contain small amounts of ALA.

Three key omega-3sWalnuts contain omega-3 fatty acid alpha-linolenic acid (ALA)

  • Two of the three most important omega-3 fatty acids are found mainly in fatty fish such as salmon and sardines: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

  • The third, alpha-linolenic acid (ALA), is found in many plants, including seeds, nuts, and some green vegetables.

  • Your body can convert a small amount—about 8%—of dietary ALA to EPA.

Posted by: Dr.Health

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