BY the time Weems W. Duvall Jr., hit 45, he was close to 300 pounds, his cholesterol was sky high and his blood pressure was out of control. "I was pretty much a walking heart attack," he says.
Diet books advised him that adding fish to his meals would help him reduce calories and take advantage of a hefty dose of heart-friendly fats called omega-3 fatty acids. He began replacing his red meat with fish and felt better -- and lost weight. As Duvall likes to put it, "I was hooked."
For years, media reports have depicted fish as a dietary dream come true -- a high-protein, low-calorie super food that protects against heart attacks, strokes and some cancers. Newer studies have even linked eating fish to lower rates of Alzheimer's disease, degenerative eye disorders, diabetes and other illnesses.
Since 2002, the American Heart Assn. has recommended that healthy adults eat at least two servings of fish a week to protect their health. "Calorie for calorie, the benefits of fish oil exceed any other nutrient in the diet," says Dr. Dariush Mozaffarian, a cardiologist at Harvard's Brigham and Women's Hospital in Boston who researches the heart benefits of fish.
But in the last few years, a battle over safety has erupted, confusing many consumers about the benefits and risks of eating fish. All fish contain low levels of contaminants (ingested from water or by eating smaller, contaminated fish), notably polychlorinated biphenyls (PCBs), cancer-causing industrial chemicals banned in 1976; and mercury, a heavy metal found in lakes, streams and oceans.
Environmentalists and consumer groups argue that toxic contaminants in some popular types of fish, such as tuna, put the public's health at risk and that the federal government is doing little to solve the problem.
Physicians and nutrition researchers, on the other hand, fear that all the talk about the dangers of fish scares people away from a food that most of medical science generally agrees offers significant benefits.
"For adults in this country, the main problem is that people don't eat enough fish," says Dr. Eliseo Guallar, associate professor of epidemiology and medicine at the Johns Hopkins School of Public Health.
Indeed, Americans are not big fish eaters. The U.S. Department of Agriculture estimates that people eat about 3.4 ounces a week, with Californians and other Pacific coast residents eating a bit more: about 3.7 ounces.
By comparison, the USDA estimates that per capita red meat consumption totals nearly 21 ounces.
"Yet fish is healthier," Guallar says.
Benefits not without risk
Scientists now think that the healthful effects of fish are largely due to substances called omega-3 fatty acids, especially two known as DHA and EPA, which are plentiful in oily fish such as salmon, trout and herring. But the long list of possible benefits (see related story) doesn't translate to a blanket endorsement of all fish, any fish.
Fish in fish sticks, for example, is generally low in omega-3s. Fish in fast food restaurants is often high in the unhealthful trans fats used to cook it.
These factors can neutralize the benefits of fish. In an investigation known as the Cardiovascular Health Study, in which 4,775 adults older than 65 were tracked for many years, those who ate baked or broiled fish one to four times each week had 27% fewer strokes than those who ate fish less than once a month. People who ate fried fish or fish sandwiches more than once a week had 44% more strokes.
"Before I did this research, I might have considered a fish sandwich at a fast food restaurant or fish sticks a 'fish meal,' " says Harvard's Mozaffarian, lead author of this work.
Another complication is that not all of the studies on fish-eating have been positive -- possibly, scientists say, because of the effect of contaminants. A study of 1,833 men in Finland, for example, reported that those who ate mercury-contaminated freshwater fish (and who ended up with higher mercury blood levels) suffered twice the rate of heart attacks and deaths from strokes as those who did not eat contaminated fish.
This raises the possibility that the presence of mercury in fish may reduce or eliminate its cardiac benefits, says Guallar of Johns Hopkins, who has conducted studies that indicate similar results.
"It's concerning," he says.
Mercury originates from natural sources and air pollution. In water, it's transformed by bacteria into methylmercury, which is toxic to the brain, heart and nervous system and especially damaging to the neurological development of infants and young children.