Fact vs. fiction

Nutrition Action Healthletter, April, 2005 by David Schardt

* Containers & packaging. "If it's food you buy in a store for microwaving, like a frozen dinner, I would be 100 percent confident in using the container it came in," says Paquette. "But remember, those are usually approved for only one use, because the polymer in the packaging can start to break down during a second use in the microwave."

"The FDA has a rigorous protocol that manufacturers of food packaging must execute every time they have new packaging components they want to use," says George Sadler. "Companies must measure how much, if any, of the packaging materials migrate into the food when they're heated in the microwave. Then the manufacturer has to undertake a rigorous toxicological evaluation to show that those levels are safe."

("Safe" means that any packaging material that ends up in the food is at less than one-hundredth the lowest level that causes harm in animal studies.) The company has to test for cancer, genetic damage, and any impact on reproduction or development.

"The FDA's testing guidelines for microwave containers pretty much cover the gamut of anything anyone would do with something in a microwave," adds Paquette, "because everybody wants to make sure they have a cushion of safety there."

Do those safeguards extend to reuseable plastic containers you buy at the supermarket? Yes, as long as they say "microwave safe," which means they've been tested for up to 240 hours in the microwave. (While other containers might be as safe, their components haven't been tested.)

* Heat susceptors. Ever wonder why microwave popcorn bags are clearly marked "This Side Up" or "This Side Down"? The bottom of the package contains a metallicized surface that absorbs microwaves and becomes hot enough to pop the popcorn.

Can that "heat susceptor" generate enough heat to trigger the release of chemicals like packaging adhesives into the food? No, says the FDA's Paquette.

"If you look in a popcorn bag, you don't actually see the silver-colored heat susceptor," she explains. "It's sealed inside a pouch in the bag itself." That helps to dramatically reduce the migration of chemicals into the popcorn oil, says Paquette.

Radiation Leaks

Do microwave ovens leak radiation?

"The FDA discontinued field testing them in the early 1980s, in part because of budget cutbacks and in part because few ovens didn't meet federal safety standards," says George Kraus of the agency's Center for Devices and Radiological Health.

In 2000, Health Canada (the Canadian equivalent of the Department of Health and Human Services) tested 60 new microwave ovens and 103 used ovens. None of the new ones, and only one of the used ones, exceeded Canada's stringent leakage limits, which are similar to the U.S. limits. The one oven that failed was 23 years old.

"Leakage of microwaves can only occur if the cooking chamber--including the metal grid over the front window and the seals around the door--has holes in it," says the University of Virginia's Louis Bloomfield.

And even in the unlikely event that your microwave does leak, you're not going to be showered with radiation. Microwaves lose intensity rapidly as they spread out. By the time they've traveled a foot of so from a small leak, they've effectively disappeared.