This is the story of Quorn.

If you've never heard of it, check Whole Foods, Wegmans, or other grocers' freezers.

The story begins in the 1960s. British scientists, worried that population growth would lead to global famine, searched for novel food sources.

Sawdust and coal didn't pan out, but dirt did. A Bucking- hamshire soil mold was found to be a good - albeit microscopic - source of protein, according to Quorn's website.

The discoverers figured out how to grow the fungus in fermenters, extract the protein, heat-treat it, mix it with an egg-based binder, and make it look and taste like meat.

In 1985, Quorn was born.

Although global famine hasn't materialized - witness the girth of many nations - the mock meat has become popular with people who think eating the real thing is unhealthy or inhumane.

The British devour 500,000 portions a day of the faux fillets, sausages, burgers,

fajita strips, lasagna, and so on, boasts Quorn, bought this year by Exponent Private Equity.

The market has been bumpier in the United States, where Quorn debuted a decade ago.

The American Mushroom Institute and veggie-burger- maker Gardenburger complained that Quorn's claim to be "mushroom- based" was deceptive. Quorn's label was changed to say it's a "mycoprotein" (myco means fungus), but advertising still says it's "an edible fungi like truffles, morels, and mushrooms."

Would it be bad for sales to just say Quorn comes from a soil fungus? David Wilson, head of Quorn's U.S. division, declined to speculate.

The biggest thorn in Quorn's side has been the Washington-based Center for Science in the Public Interest. Best known for outing fat-laden foods, CSPI said this month that it had received 1,700 reports of severe reactions to Quorn. It wants regulators to ban the product.

"With so much concern about peanuts and shellfish," said CSPI executive director Michael Jacobson, "it made no sense to us to introduce a powerful new allergen."

The U.S. Food and Drug Administration says Quorn's bad-reaction rate is "well below" that of common allergens such as wheat. But the agency concedes that mycoprotein may make "highly sensitive consumers" suffer "gastrointestinal effects which are, judging from the reports, very unpleasant."

"Like the worst food poisoning ever," said Lauren Fields, 27, a Philadelphia artist and Quorn casualty.

Fields, a vegetarian, is a fan of Quorn and had no problem for about 10 meals.

"I didn't make the connection until I was sick four times," she recalled. "An hour or two after eating [Quorn], I had abdominal pain, vomiting, and diarrhea until 5 a.m. And each time, I got sicker."

Keep Quorn on the market, Fields says, but beef up the labeling. It now says, "Mycoprotein is high in protein and fiber. This may cause intolerance in some people."

Says Fields: "They need to put a warning on it."

- Marie McCullough