The corn plant has more genes than a human being. It's no wonder then some worry that modifying crops to make them more nutritious or disease-resistant may have unintended genetic consequences.

As the debate between advocates and critics of genetically modified foods simmers worldwide, a new opinion enters the mix. A report from the National Academies' National Research Council and Institute of Medicine suggests methods to screen and track new genetically modified foods.

The National Academies report says that genetically modified foods now on the market are safe. However, problems have arisen in the past. For example, report co-author Dean DellaPenna says a few years ago a new potato species turned out to have abnormally high levels of the naturally occurring toxin solanine, and had to be pulled from the market.

Commissioned by several U.S. government agencies, the report focuses on methods to discover and avoid such unintended side effects in the future.

Lisa Dry of the Biotechnology Industry Organization in Washington, says the recommendations are based in science.

"The report clearly states that the foods that are in the marketplace today are very safe,? she said. ?This report is intended to be more forward looking. As scientists and researchers start doing more extensive and wider crossbreeding, they want to be certain that those potential outcomes, which may (bring) beneficial changes, as well as potentially adverse situations are thoroughly reviewed and that the regulatory system is set up to examine them to be sure that we have a safe food supply."

Co-author Jennifer Hillard of the Consumer's Association of Canada says screening and surveillance should apply to all genetically modified plants and animals, not just those created through genetic engineering. The term "genetic modification" includes new breeding crosses as well as genetic engineering, or inserting a gene from another organism.

The report's main suggestion employs the relatively new fields of genomics and proteomics, which let scientists look at thousands of genes and proteins at the same time. Using these tools, it asks for a public database of information about the many genes and proteins in a particular food, including information on the amounts of nutrients, allergens, and toxins.

A new genetically modified food would be compared to this database before entering the commercial market. It would be flagged for further testing or post-market surveillance if any protein falls outside normal ranges. The report also calls for developing better techniques to sample crops, to find toxins and allergens, and to analyze the large amounts of crop data.

Doug Gurian-Sherman, senior scientist at the non-profit Center for Food Safety in Washington, says that the National Academies report proves how much scientists do not know about the potential risks of genetically modified foods.

"We don't really know how these unintended effects occur - they're not predictable based on what we know about the gene that we're putting in the crop, or the crop,? he said.

Mr. Gurian-Sherman believes that while the report's guidelines are basically sound, food growers and regulators must interpret them very cautiously. He notes that scientists may have some tools they could use to better catalog genetically modified foods, but these tools do not yet explain how unintended changes occur.

"I would say as a scientist, that unless we understand how these things occur, we don't have the predictive value to understand how big the risks might be,? Mr. Gurian-Sherman said. ?And when we don't understand how big the risks might be, I think that warrants, with something as vital as our food, a cautious approach."

The report's authors say that the genetic assessment they are calling for would be something food growers would do themselves, but they did not explain how these companies should be made to comply. They also suggest that having more data on genetically modified foods may change how products containing them are labeled in stores.