What do a fish and a tomato have in common?

Genes.

That's not a punchline.

Science's ability to manipulate the foods we eat -- putting a fish gene in a tomato plant to improve tomatoes, for example -- has sparked debates and opposition. From a local store opposing genetically modified foods to U.N. negotiations in Canada last month that produced international trade rules to allow countries to ban their import and make exporters label their products.

According to Becky Brown, of Natural Health Organic Foods in Cape Girardeau, the biggest concern about genetically modified, or GM, foods is the unknown -- a yawning gap in the knowledge of what GM foods will do to humans and the environment.

Food companies "slipped it on us without giving us a choice," she said.

There have been some studies, though. Last year the British medical journal The Lancet published a study of the effects of potatoes on the growth of rats. The potatoes had been given a gene from a flower to produce a natural insecticide. The study found the rats didn't grow normally.

But that study was marred by some deep flaws, according to Dr. Georganna Syler, a nutritionist/dietitian at Southeast Missouri State University.

The measurements were crude and the results contradictory, she said. Perhaps worst of all was that the rats weren't fed much protein.

"It's no wonder they didn't grow," she said.

She added that that many non-foods are widely accepted, yet produced through genetic modification. The insulin diabetics inject, for example, doesn't come from humans; it's bio-engineered.

On the other hand, a study last year by Cornell University found that Monarch butterfly larvae died after eating the pollen from Bt corn, which contains bacteria to kill European corn borer worms. In January, the Environment Protection Agency told seed companies they must tell farmers about "voluntary measures" to protect the butterflies. The EPA also put restrictions on how much Bt corn can be planted in one place to prevent the corn borer from becoming immune to it.

Texas-based snack maker Frito-Lay Inc. announced Jan. 31 to its suppliers that it will stop using genetically altered corn.

The American Farm Bureau Federation, which says biotechnology can be used to produce larger and more nutritious crops, accused Frito-Lay of caving in to anti-biotech activists.

"People like Frito-Lay are responding to small splinter groups out of fear they're going to be boycotted," said Joseph Fields, a spokesman for the farm group. "We feel the companies are overreacting."

Frito-Lay's action follows last summer's announcement by Gerber and Heinz that they would stop using genetically modified ingredients in baby food even though they believe the ingredients are safe.

Enough nutrients?

A concern of some groups is that genetic manipulation may unintentionally manipulate nutrients right out of food.

That is simply not true, Syler said.

"Many foods are being altered to increase their nutritional value," she said, pointing to a new strain of rice that will have more vitamin A in it. Rice is a staple item in over half the world, yet it is poor in nutrients such as vitamin A, which can prevent childhood blindness.

"I believe GM is not at all a threat. It's just speeding up natural processes," she said.

Syler said "the fury of concern" over GM foods started last year in Europe, when Prince Phillip of Britain came out against them. He has the power of persuasion, she said, but no scientific backing.

It is true that there haven't been extensive tests on modified foods, Syler said. But that's true of a lot of things, such as herbal supplements.

"Much ado about nothing," she said, summing up. "It's not a big deal."

More allergies?

Another concern is that modified foods may bring cause new food allergies.

That's conceivable, said Dr. Tom Critchlow, a Cape Girardeau allergist, but he hasn't seen anything in the medical literature to say that there any documented cases.

The thing is, allergies are usually more complicated than people think. There is a genetic predisposition in some people to have allergies, Critchlow said, but there's also an environmental factor.

Some doctors think that childhood infections may prevent future allergies, although that hasn't been proven yet.

While there has been an increase in respiratory allergies over the past century, he said, it's hard to say anything about the number of food allergies because the condition is overdiagnosed.

While GM foods could conceivably cause some new allergies, they could also be used to reduce them, Critchlow said. In some foods, the exact compound that causes allergic reactions is known. Theoretically it's possible to modify those foods to eliminate that compound, though there may not be a big enough market for non-allergenic food to satisfy a company's bottom line.

Syler also said that GM foods could possibly cause some allergies, but that that wouldn't be any different than a new food doing the same. When kiwi fruits were first imported to the United States, some people were allergic to them, she said, yet you can still buy kiwis in the grocery store.

Eating organic

But if someone prefers to eat organic foods, it will be a challenge to live up to it. About 70 million acres of GM crops were planted in the entire world last year. In the United States, GM varieties accounted for about a third of corn and half of soybeans and cotton planted, Syler said.

Corn is turned into corn syrup, which is used to sweeten everything from cookies to soda pop. Even the corn in your tortilla chip is organic, it might have been fried in oil from GM corn, soybeans or cottonseeds.

Most cheeses made in the United States use a genetically engineered rennet, the enzyme that makes milk coagulate into curds.

But it is possible to eat mostly organic foods. "You have to really watch your labels and watch what you're eating," Brown said. "We're seeing more and more companies label their product GMO (genetically modified organism)-free." If you eat out, more than likely there'll be GM foods somewhere in the menu items. But as for cooking at home, you can control what you eat.

Some people are doing just that, because in its four years of business, Natural Health has seen a steady growth of business, she said.

Organic foods are more expensive than non-organic foods, but the amount varies, Brown said. Carrots might only be slighter higher, while grapes would be cost much more.

Apart from nutritional supplements, the store's most popular items are soy-related: soy milk, tofu, soy cheese, soy sour cream, soy cream cheese. Over the holidays, the store sold a "tofurkey" (not to mention 100 free-range antibiotic-free turkeys).

One of Natural Health's best customers is Luella Stadt of Jackson.

"I almost live here," she said after pulling some organic ice cream and yogurt out of the freezer.

Stadt has been eating organic foods about a year. In that time, she said, she has been feeling better.

"I would be dragging along, sitting in a rocker by now" without organic foods, she said. "It's organic for me, organic and natural. That's the way God made it."

She's been trying to convince her son to try organic foods, such as soy milk. Many years ago in grade school, Stadt said, she used to milk cows. Cows that had just given birth sometimes got infections, and the milk of infected cows had pus and lumps in it. She wondered how you could see that kind of thing with mechanical milk machines.

"It doesn't take much to convince people when they hear something like that," she said.

Her son tried soy milk. And liked it.

The Associated Press contributed some information to this story.