You've heard that fish is good for you, but can you get the same benefits from a fish oil pill?

Some studies have found that fish oil supplements are beneficial for women with high-risk pregnancies and people with heart problems. But health and nutrition experts say these supplements need to be studied further and urge consumers not to use them without a doctor's approval.

We're just not there yet. We're still a bit anxious about recommending exposure or treatment, says Donald Mattison, M.D., the medical director of the March of Dimes, which has sponsored studies on the role of fish oil in preventing premature births.

The American Heart Association's (AHA) new dietary guidelines recommend eating two servings (6 ounces) of fish every week, but the AHA says there is no compelling evidence that fish oil supplements benefit cardiovascular health.

The best advice at the present time is to have cardiac patients talk to their doctors about fish oil supplements. For some it may be warranted but only under a doctor's approval, says Penny Kris-Etherton, a distinguished professor of nutrition at Penn State University and one of the authors of the AHA's dietary guidelines.

Your heart and fish oil

Fish is the best source of omega-3 fatty acid, a polyunsaturated fat that may reduce your risk for heart disease and heart attack.

People who eat fish regularly reduce their risk for heart attack even if they already have coronary heart disease. Fish oil may also help to prevent irregular heartbeats and reduce triglycerides, a fatty substance in your blood, Kris-Etherton says.

The AHA recommends fish oil capsules only for patients with severely high triglycerides (greater than 1,000 mg/dl) who have not responded well to other treatments, such as dietary changes or medication, and are at an increased risk of inflammation of the pancreas.

However, Kris-Etherton and the heart association say fish oil pills can cause side effects, such as an upset stomach, excessive belching, increased bleeding, more nosebleeds and bruising easily.

Fish oil and premature delivery

In the case of pregnant women, could fish oil supplements be safer than eating certain kinds of fish? Perhaps, because the U.S. Food and Drug Administration (FDA) is advising pregnant women, women of childbearing age, nursing mothers and small children to avoid eating shark, swordfish, king mackerel and tilefish.

These large fish contain high levels of mercury, which can harm an unborn baby's developing nervous system, the FDA says. Shellfish, canned fish, smaller ocean fish, or farm-raised fish are safe for pregnant woman and women of childbearing age, the FDA says.

Some researchers believe fish oil pills may prevent premature labor, but studies have not conclusively found that to be true, Mattison said. Some results have been encouraging, however, such as research sponsored by the March of Dimes of nearly 1,000 women with pregnancy complications that found daily fish oil supplements cut the risk for premature delivery in half.

However, for women carrying twins, the daily intake of four to nine fish oil pills had no benefits, according to the study by the Danish Epidemiology Science Center in Copenhagen. Bleeding in the brain occurred in seven babies whose mothers received fish oil supplements, compared with three babies in the group that received olive oil instead of fish oil, according to a study published in the British Journal of Obstetrics and Gynaecology.

Mattison said women at high risk for premature delivery should explore the benefits of fish oil supplements with their doctor. Researchers have not yet found the causes of premature delivery, but women who smoke or who previously gave birth prematurely are in the high-risk category, Mattison says. Women who were born prematurely or have sisters who gave birth prematurely also may be more susceptible, he says.

Good sources of good fish fat

Many foods that contain omega-3 fatty acids also have high amounts of N-6 fatty acids, a polyunsaturated oil which can increase your risk of developing a heart attack by lowering the cholesterol proteins that help keep your arteries unclogged. American consume 17 times more N-6 fatty acids than omega-3 fatty acids but should be eating only five times as much N-6 fatty acid as omega-3 fatty acid, says Paul Addis, Ph.D., a professor of food science and nutrition at the University of Minnesota. Baking, broiling or grilling fish avoids the use of vegetable oil, a common source of N-6 fatty acid.

If you want a healthier diet, Addis says these fish have high levels of omega-3 fatty acid:

1. Albacore

2. Black bass                                        

3. Bluefish

4. Carp

5. Channel catfish

6. Herring

7. Lake herring

8. Lake trout

9. Mackerel

10.Pompano

11.Salmon

12.Tuna (packed in water)

13.Whitefish