Here's a look at the science behind the scares

By Kathleen Zelman, MPH, RD, LD
WebMD Weight Loss Clinic - Expert Column

Amid the flurry of headlines about the food industry, it's a challenge to figure out what is safe to eat: Is mad cow disease a real threat? Does farmed salmon cause cancer?

Many consumers are racing to buy organic foods to avoid potential toxins in their grocery carts. But are we overreacting, or is there really cause to shun our food supply?

When it comes to two of the most recent foods called into question -- beef and salmon -- it boils down to a matter of risk vs. benefit. To help you decide whether these foods are for you, let's take a serious look at the science behind the headlines.

The Salmon Scare

A report in the January issue of the journal Science touched off alarm that farmed salmon contained levels of polychlorinated biphenyls (PCBs, a kind of dioxin) that could be harmful. The concern over PCBs stems from their role as a likely carcinogen in humans, based on studies in animals.

In an ideal world, there would be no PCBs. But unfortunately, they exist in the air that we breathe and in many foods we eat, including chicken, butter, and both wild and farmed salmon. PCBs get into wild salmon from the other fish they eat and into farmed salmon from their feed (which contains many of these same fish).

The FDA has set the safe upper limit for PCBs at 2000 parts per billion (ppb). Farmed salmon averages 27 ppb, well below that limit. The controversy has come about because another branch of the government, the Environmental Protection Agency (EPA), has set a much lower safe limit for PCBs in food -- 4.5 times lower, in fact.

Keep in mind that these two agencies are charged with different functions. The EPA sets limits meant for recreationally caught fish, while the FDA's limits are intended for fish sold commercially. The FDA's higher limit is also supported by the World Health Organization and the European Union.

Although the amount of PCBs found in most fish is only 1/80th of the FDA safe level, ''The farmed salmon industry is working to further reduce PCBs in fish feed while maintaining the healthful omega-3 fatty acid content,'' says Alex Trent, executive director for the industry group Salmon of the Americas.

The American Heart Association maintains that eating two servings a week of oily fish (like salmon) can help healthy adults ward off sudden cardiac death, thanks to the protective effects of omega-3 fatty acids. The best source of these omega-3 fatty acids is farmed salmon, though they're also found in flaxseed, walnuts, soybeans, and oils made from these products.

Many longstanding studies have documented the health benefits of a diet rich in omega-3 fatty acids and their role in guarding against heart disease. More recent studies have indicated that omega-3s may even help keep your mind agile and protect against Alzheimer's disease. And salmon, like other fish, is an excellent, low-fat source of protein that many people enjoy eating.

What can we conclude from this? It's a decision each of us needs to evaluate personally, of course. But for most healthy adults, the health benefits of salmon far outweigh the much smaller and less-clear risk that the PCBs found in it could cause cancer. (Children and pregnant or nursing women may be at increased risk of exposure to contaminants and should check with their doctors for advice on eating all kinds of fish.)

Let's put the issue into perspective. The leading cause of death in the U.S. -- causing 950,000 deaths a year -- is cardiovascular disease. Eating two meals per week of fatty fish, such as salmon, can reduce the risk of fatal heart disease by 40%. The dangers of eating salmon, meanwhile, are unclear, largely theoretical, and based on studies in animals. The risks would appear to be much smaller than that of developing heart disease.

If you are concerned about PCBs, remove the skin and dark flesh from your salmon, and cook it so that the fat drips off -- thus reducing PCBs by 20%-30%.

How Safe Is Our Beef Supply?

Because we eat so much beef in the U.S., it's especially important that we be confident of its safety. The CDC says that the risk of a consumer in this country contracting the human form of mad cow disease is "extremely small." In testimony presented to the Senate, CDC Director Julie Gerberding said U.S. authorities had taken adequate steps to reduce the risk.

Studies have revealed that the agent responsible for mad cow infections is not found in beef muscle or in milk. The disease is spread by proteins called prions, which are found in the central nervous system tissue -- such as the brain and spinal cord -- of cattle. Prions cannot be destroyed by cooking.

Only one cow infected with the disease has been found in the U.S. According to the National Cattlemen's Beef Association, the central nervous system material from that cow -- found in Washington State -- did not enter our food supply. And the entire herd associated with that cow has been slaughtered and disposed of.

Since that case, the government has banned so-called "downer" cattle -- those that are unable to walk -- from being used as food for humans. And it now prevents processors from using cattle brains and small intestines from older cattle in human food. Still more regulations may be established to ensure that our supply of beef remains safe.

Looking for an extra measure of food safety? When beef is ground, there is a miniscule risk that nerve tissue will accidentally be included. But solid cuts of boneless meat are prion-free. So if you're looking for that extra level of safety, buy whole cuts of beef and ask the butcher to grind them for you.

American consumers should feel confident that the government is doing its job to be sure our food supply is among the safest in the world. Be sure to do your part as well. Once you get the food home from the market, practice safe food handling -- from clean cutting boards to proper cooking temperatures -- to keep your family safe.

SOURCES: Neurology, January 2004. Science, January 2004. Annals of Internal Medicine, 1999; vol 130.

SLIDESHOW

Diet-Wrecking Foods: Smoothies, Lattes, Popcorn, and More in Pictures See Slideshow

Health Solutions From Our Sponsors