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"
Source: Foodfuture, Food and Drink
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
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,
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.
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).