Getting plenty of heart-healthy omega-3 fats used to mean eating fish or taking supplements.

But grocery aisles these days are packed with food labels boasting of omega-3 content. You can buy milk, eggs, yogurt, cereal, orange juice, butter substitutes, mayonnaise and other products that carry the claim.

Behind the boom: studies that show certain omega-3 fats can help prevent fatal heart attacks and offer other heart benefits; less conclusive research hints at brain and eye benefits and possible anti-cancer effects.

But don't cross fish off your shopping list yet, nutrition watchdogs say. That's because many of the new products contain little or none of the omega-3 fats backed by the most scientific evidence: DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid).

"The numbers are tiny, but the claims they are making are huge," says Katherine Tallmadge, a Washington, D.C., registered dietitian and spokeswoman for the American Dietetic Association.

"It's all very confusing," says Bonnie Liebman, a nutritionist with the Center for Science in the Public Interest. She reviewed omega-3 food claims for a recent newsletter article (at www.cspinet.org).

Her conclusion: Consumers are in real danger of being misled. Even a careful label reader won't learn, for instance, that a carton of Breyer's Smart DHA Omega-3 yogurt has less DHA than a teaspoon of salmon.

And that bottle of Hellman's mayo proclaiming the product is "naturally rich in Omega-3 ALA"? True enough, Liebman says: Most mayonnaise is made with soybean oil, which is a source of ALA (alpa-linolenic acid). But that kind of omega-3 fat, found most abundantly in flaxseed, has not been proven to convey the same health benefits as DHA plus EPA, she says.

One study even suggested high intakes of ALA might increase the risk of prostate cancer. But that finding "doesn't make any sense to anyone at this point" and needs more rigorous study, says William Harris, a heart researcher at the University of South Dakota.

Harris, who has advised companies making omega-3 products, says he sees little downside to the grocery-store glut as long as consumers know what they are getting. "But if the label just says omega-3 and makes no mention of DHA and EPA, there's a good chance it's ALA. So it can be a little deceptive."

Tallmadge's advice: "Eat fish." Those concerned about mercury, including pregnant women, can choose low-mercury varieties such as salmon and sardines, she says. Walnuts, ground flaxseeds, tofu and other whole foods containing ALA also are great additions to any diet, she adds, even if the evidence for that fat is not as compelling. There's no need to buy "manufactured kibble" spiked with omega-3 fats, she says.

Vegetarians can take algae oil supplements to get DHA, she says. Others who just don't eat enough fish can take fish oil supplements. But read the labels carefully, she warns, looking for levels of DHA plus EPA.

Studies suggest an average of 500 milligrams a day is beneficial, Liebman says. You can get that much by following the American Heart Association's advice to eat fish, particularly fatty fish, at least twice weekly. The association says patients with coronary heart disease should get 1,000 milligrams of DHA plus EPA daily.

HOW MUCH OMEGA-3 FAT?

All food sources of omega-3 fats are not created equal. Here are the amounts of DHA and EPA, the omega-3 fats backed by the most promising studies, in some foods:

FOOD ... DHA(PLUS SIGN)EPA (MG)

Atlantic salmon, farmed (6 oz. cooked) ... 3,650

Coho salmon, farmed (6 oz. cooked) ... 2,180

Swordfish (6 oz. cooked) ... 1,390

Bumblebee salmon (Red, Pink or Blueback, 3 oz.) ... 1,200

Sardines in vegetable oil, drained (3 oz.) ... 840

Fish sticks (6) ... 680

Shrimp (3 oz.) ... 270

Smart Balance Omega Plus Buttery Spread (1 tbsp.) ... 160

Land O Lakes Omega-3 Eggs (1 egg) ... 150

Breyers Smart DHA Omega-3 yogurt (6 oz.) ... 30

Horizon Organic DHA Omega-3 milk (1 cup) ... 30

Silk Plus Omega-3 DHA Soy Milk (1 cup) ... 30

Source: Center for Science in the Public Interest (www.cspinet.org)