S ome nutrition experts and geneticists have expressed concern that genetically engineered foods will have unintended, and dangerous, side effects.

To learn more about the potential dangers, Bottom Line/Personal spoke at length with biotechnology specialist Sheldon Krimsky, PhD:

What exactly is genetic engineering? It’s a technique for snipping individual genes from one organism (plant, animal or microbe) and slipping them into another. This is done to introduce new traits or to enhance existing traits in crops.

One common goal of genetic engineering is to render crops resistant to attack by insects and the herbicides applied to control weeds.

Another goal is to lengthen the time span that fruits and vegetables stay fresh.

The Flavr Savr tomato, which made headlines when it was introduced in 1993, contained a gene that suppresses polygalacturonase, an enzyme that causes ripening.

Are genetically engineered foods safe to eat? There’s no evidence to suggest that genetically altered foods are harmful or that they’re less nutritious than their unaltered counterparts.

However, there is no compelling evidence that they’re safe either. That’s because food producers are not required to conduct safety tests on genetically engineered foods which they deem to be equivalent to the natural foods from which they are derived.

Perhaps of greatest concern is the use of genetically engineered bovine growth hormone (BGH), which is widely used in the dairy industry to increase cows’ milk production.

Cows given BGH are more likely than other cows to develop mastitis, an infection of the udders.

Preliminary research involving animals suggests that drinking milk from cows treated with BGH causes high levels of insulin-like growth factor (IGF-1), which are linked to higher cancer risk.

Also, since infections are more common among cows that have been given genetically engineered BGH, they receive more antibiotics.

If dairy farmers could ensure that these powerful drugs didn’t get into the human food supply, this might not matter. But antibiotics do slip through.

Widespread use of antibiotics, by doctors as well as food producers, has contributed to the surge in antibiotic-resistant streptococcal infections and other bacterial infections.

What can I do to protect myself? Given what we now know, it’s prudent to buy dairy products from producers who don’t use BGH.

This information is sometimes included on carton labels. I look for it when I buy milk.

Which other foods are likely to have been genetically modified? Today, nearly 60% of soybeans sold in the US have been genetically modified using gene-splicing techniques.

Other crops whose DNA has been altered include apples, broccoli, cranberries and peanuts. These are not yet on the market, but may be soon.

Except for soybeans, corn and some varieties of tomatoes and potatoes, few "whole" foods on the market have been genetically modified.

It’s difficult to avoid genetically modified soybeans because they’re an ingredient in so many different products. I don’t even bother looking for it on the label.

I do try to avoid genetically engineered foods when doing so is feasible. I buy organic produce because I know that organic trade organizations do not certify foods that have been genetically modified. And I buy free-range chicken because I know that it hasn’t been treated with hormones.

If you don’t have access to organic foods, or prefer not to pay the premium price, consider buying produce at a local farmers’ market. Small farms are less likely than large growers to use genetically modified seeds.

Isn’t gene-swapping a problem for those with food allergies? It can be. The FDA now requires food producers to alert consumers when a genetically engineered food contains a known allergen.

In one highly publicized case, a company was considering transferring a gene from a Brazil nut into a soybean. Then a study showed that individuals allergic to Brazil nuts also became allergic to the genetically modified soybeans. Ultimately, the company did not market the soybean.

Currently, there is no required testing for new allergens created by genetically modified foods. Consequently, as genetic engineering becomes more common, people may find themselves experiencing allergies to foods that never gave them problems before.

Do genetically engineered foods taste different? Food producers say there’s no difference, but I’m not so sure.

Once I asked my students to do a blindfolded taste test on two tomatoes, one of which had been genetically modified. The genetically engineered tomato looked fantastic, but it wasn’t nearly as tasty.

With other foods, you may never notice the difference.