The broad (fave) bean (Vica faba vulgaris), a common food of the Mediterranean region, contains the toxins vicine and convicine at a level of about 2 percent of the dry weight.

“A fabis abstinete,” Pythagoras exhorted. “Abstain from beans.” Pythagoras forbade his followers to eat the beans, presumably because he was one of the millions of Mediterranean people with a decifiency of glucose-6-phosphate dehydrogenase. This deficiency results in a low glutathione concentration in blood cells, which causes increased resistance to the malarial parasite, probably accounting for the widespread occurence of the mutant gene in malarial regions. However, the low glutathione concentratrion also results in a marked sensitivity to agents that cause oxidative damage, such as the fava bean toxins and a variety of drugs and viruses. Sensitive individuals who ingest the fava beans develop a severe hemolytic anemia caused by the enzymatic hydrolysis of vicine to its aglycone, divicine, which forms a quinone that generates oxygen radicals.

Bruce N. Ames, "Deitary carcinogens and anticarcinogens," Science, 221, 1256 (1983).

Though the casual relationship between beans and flatulence had long been suspected, it wasn't until about 15 years ago that reseachers could explain why beans do, in fact, produce gas. Now it seems modern science might even be able to take the malodorous "music" out of beans and other legumes.

The seeds of legumes - everything from chick-peas and lentils to navy beans, string beans and soybeans - contain chains of sugar molecules called oligosaccharides. Some of these chains contain a molecule known as alpha-galactose, which is actually made up of galactose and an alpha link that joins galactose and other sugar molecules. Problems arise because human digestive enzymes cannot break this alpha link. Thus some sugar chains, including such champion gas producers as raffinose, stachyose, and verbascose, pass relatively intact through the gastrointestinal tract. But when the sugar chains reach the large intestine, anaerobic bacteria, which live peaceably in mammalian guts and metabolize food in the absence of oxygen, break down the oligosaccharides by fermentation. As metabolic by-products, these bacteria typically produce hydrogen, carbon dioxide, and sometimes, methane. The result is a buildup of gas in the intestinal tract that can produce nausea, diarrhea, cramps, and social discomfort. The onomatopoetic term for that bubbling, gurgling, rumbling tumult in the belly is borborygus. If the anaerobic digestion occurs farther up the gastrointestinal tract, those same gases are absorbed into the blood and ultimately exhaled--beans get you coming and going.

The quest for a gas-free bean has been unofficially underway for decades, according to Joseph Rackis, a research chemist with the USDA. "Even in World War II," says Rackis, "pilolts were under strict orders not to eat beans or legumes because gas expands in the reduced pressure at high altitudes, and the pilots would be much more flatulent than on the ground. The Air Force thought it was serious enough to do research."

V.S. Rao and U.K. Vakil at the Bhabha Atomic Research Centre in Bombay, India sed seeds of a legume called green gram in distilled water then exposed the seeds to radioactive cobalt-60. The radiation, Rao and Vakil discovered, apparently weakens some of the links in the sugar chains--just enough so that the oligosaccharides become much more susceptible to digestion. In fact, 50 percent of stachyose and raffinose, the two main culprits in flatulenc, breaks down after being exposed to a radioactive dose equal to 250,000 rads, which doesn't make the food radioactive. "Substantial reduction in stachyose, which induces maximum flatus," Rao and Vakil delicately conclude in a recent issue of the Journal of Food Science, "...is of practical importance."