Genetic tinkering to improve the nutritional value of crops can inadvertently trigger life-threatening food allergies, an experiment found.

Soybean plants were given a gene from Brazil nuts that gives them more sulfur-rich amino acids. This makes the soybeans a more nutritionally balanced food, especially for livestock.But researchers found that the gene-engineered soybeans could trigger reactions in people who are allergic to Brazil nuts.

The Associated Press first reported the results of the experiment two years ago. They are now being published in Thursday's issue of the New England Journal of Medicine.

In allergic people, Brazil nuts can trigger reactions ranging from mild itching to sudden death.

Animal testing suggested that the soybeans would not trigger serious allergic reactions. But exposing people to them showed other-wise. The human testing was conducted by Julie A. Nordlee and others from the University of Nebraska.

The study was financed by Pioneer Hi-Bred International of Johnston City, Iowa, which produced the genetically engineered soybeans. The company has abandoned plans to sell them.

Genetic engineering involves giving new traits to bacteria, plants and animals by transferring genes from other forms of life.

In this case, the goal was to produce soybeans containing more of the amino acid methionine.