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Eating foreign DNA

When scientists make a transgenic plant, they insert pieces of DNA that did not originally occur in that plant. Often these pieces of DNA come from entirely different species, such as viruses and bacteria. Is there any danger from eating this "foreign" DNA?

Source: Foodfuture, Food and Drink Federation

We eat DNA every time we eat a meal. DNA is the blueprint for life and all living things--cows, chickens, corn, wheat, mushrooms, E. coli, and some viruses--contain DNA in many of their cells. We eat the DNA of bacteria and viruses without intending to because those organisms are found clinging to the meats, cereals, and vegetables that we eat. Some of this DNA is similar to our human DNA, but much of it is foreign to us.

What happens to this DNA? Most of it is broken down into more basic molecules when we digest a meal. A small amount is not broken down and is either absorbed into the blood stream or excreted in the feces.

Researchers in Germany (Schubbert et al., 1997) fed mice a harmless detectable DNA sequence and tracked its progress through the gastrointestinal tract and the body. About 5 percent of the DNA, consisting of short pieces 100 base pairs to 1700 base pairs long, was detectable in the small intestine, large intestine, and feces up to 8 hours after a meal. Very small amounts of DNA, about 0.05 percent of the amount originally present in the meal, were found in the blood stream up to 8 hours after eating. These pieces could be up to 700 base pairs long. Fragments of the foreign DNA were also found in the liver and spleen up to 18 hours after a meal. Tests detected no foreign DNA 42 hours after a single meal.

This experiment has been done with three different kinds of DNA: a sequence from the M13 virus that attacks bacteria, the GFP gene that allows jellyfish to produce a green fluorescent color, and the rubisco gene that is involved in photosynthesis in plants. In all three instances, small amounts of the foreign DNA could be detected in the internal organs of mice after the meal (Doerfler, 2000).

When pregnant mice were fed meals containing traceable DNA, the DNA was detected in various organs of the fetuses and newborn mice. This indicates that the foreign DNA can travel from the mother's bloodstream through the placenta to the fetus. Some of the DNA is found closely associated with mouse chromosomes, leading to speculation that it has been incorporated into the chromosomes (Doerfler, 2000).

In contrast to the experiments showing persistence of foreign DNA in mice, an experiment with chickens showed that foreign DNA is quickly broken down. Researchers in Britain (Chambers et al., 2002) fed transgenic maize to chickens and looked for transgenic DNA sequences in the crop, stomach, and intestine of the birds. Some DNA sequences were detected in the crop and stomach, but none in the intestine, indicating that the DNA was quickly broken down by the digestive process in chickens.

DNA may be quickly destroyed in sheep, also. In laboratory tests, British researchers (Duggan et al, 2000) extracted DNA from transgenic maize and mixed it with saliva and stomach fluid from sheep. DNA sequences were still detected in the DNA-saliva mixture after 24 hours, but DNA was destroyed by the stomach fluids within one minute.

What happens to foreign DNA that finds its way into the tissues of an organism? We suspect that the body's normal defense system eventually destroys fragments of foreign DNA. If some fragments are incorporated into the DNA of the host, they might be inactivated by mechanisms that control the activity of genes. Further research in this area would help to determine exactly how humans have managed to eat DNA for thousands of years without noticing any effects from the tiny bits that sneak into the bloodstream. So far there is no evidence that DNA from transgenic crops is more dangerous to us than DNA from the conventional crops, animals, and their attendant micro-organisms that we have been eating all our lives.

Questions have been raised about one piece of DNA in particular, the DNA from the cauliflower mosaic virus that has been widely used in making transgenic plants. This topic is addressed in the segment on the CaMV promoter.

For an opinion that eating transgenic plants poses no threat to human health, see the British Royal Society's 2002 report "Genetically modified plants for food use and human health--an update" (http://www.royalsoc.ac.uk/files/statfiles/document-165.pdf).

Page last updated : March 11, 2004

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