Experts say within several years there will be new GM foods with taste and nutrition improvements: cooking oils with less trans fat, tastier potatoes and peanuts that don't trigger allergies.

At North Carolina State University, one of the biggest U.S. plant breeding programs, scientists are developing drought-tolerant wheat and are a couple years from field testing GM peanuts that have no life-threatening allergens, said Steven Leath, associate dean for health research.

At Rutgers University's agricultural college, plant biology professor Nilgun Tumer and colleagues modified potatoes to better keep their flavor when processed as french fries and to limit browning when sliced, but she said farmers haven't adopted the new varieties. Now her team is trying to give tomatoes a gene to make a compound that helps prevent cancer and osteoporosis.

Lisa Lorenzen, a liaison to the biotech industry at Iowa State University, said most Americans haven't worried about GM foods because they trust the regulatory system. She said many Europeans oppose GM foods because they don't trust governments that wrongly insisted for years that the beef supply, tainted by mad cow disease, was safe.

Opponents say genetically modified foods could cause allergic or toxic reactions and harm the environment. Worries include the mixing of GM crops with regular ones either by handlers, or pollen — already documented — and GM foods being sold where they're not approved.

On Tuesday, a Swiss biotech company said it mistakenly sold U.S. farmers an experimental, unapproved GM corn seed, and tons of the resulting corn was sold between 2001 and 2004. U.S. government agencies say there was no health or environmental risk.

In 2000, recalls, lawsuits and public uproar followed disclosure that StarLink GM corn, approved only for animal use, had gotten into taco shells and chips.

University plant scientists, industry, the Food and Drug Administration and numerous European science agencies say GM foods are safe.

"Nobody's been able to prove that anyone's even gotten the sniffles from biotechnology," Childs said.

But Margaret Mellon of the Union of Concerned Scientists, said there's no system to track health problems caused by GM foods.

Her group, along with the Center for Science in the Public Interest, has long pushed for labeling — only required when GM products have properties different from ordinary foods, such as a higher nutrient content. They contend consumers deserve a choice if they want to avoid GM foods and they also want government regulation.

Currently, companies developing GM foods voluntarily send their data to the FDA, but there's no official approval before products go on sale.

"It's left up to the good nature of Monsanto or DuPont or other companies to do the right thing," said Gregory Jaffe, director of the biotechnology project at CSPI.