How do genetically
engineered foods compare with conventional foods in
nutritional quality? This is an important issue, and
one for which there will probably be much research in
the future, as crops that are engineered specifically
for improved nutritional quality are marketed. However,
the potential for engineering nutritional traits has
so far taken a back seat to goals such as pest resistance
and herbicide tolerance. Thus, there have been only
a few studies to date comparing the nutritional quality
of genetically modified foods to their unmodified counterparts.
The central question for GE crops that are currently
available is whether plant breeders have accidentally
changed the nutritional components that we associate
with conventional cultivars of a crop. The isoflavone
content of soybeans is a nutritional component
that has been investigated because of its potential
for preventing disease. Some isoflavones are converted
by the body into phytoestrogens, which are believed
to help prevent heart disease, breast cancer,
and osteoporosis. Soy is added to many health
foods to increase dietary isoflavones.
People who eat soy products for the health benefits
are interested in whether RoundupReady soybeans,
which have been genetically engineered to allow
them to survive being sprayed with Roundup herbicide,
contain the same amount of isoflavones as conventional
Source: Mark L. Tucker, USDA/ARS
et al. (1999) in their study of herbicide-tolerant
soybeans (abstract available at http://www.biotech-info.net/phytoestrogens.html)
reported that the RoundupReady soybeans they studied
contained 12-14% less isoflavones than unmodified soybeans.
If RoundupReady soybeans have reduced isoflavones, they
would be less "healthy" for us than conventional
On the other hand, it has also been suggested that
RoundupReady soybeans contain unnaturally high amounts
of isoflavones, enough to cause uterine cancer in mice.
for a brief discussion of this research.) If this were
true, Roundup Ready soybeans would be "unhealthy"
for the opposite reason: too much instead of too little
of the isoflavones that we hope will prevent cancer
and heart disease.
Research published by employees of Monsanto (Padgette
et al., 1996; Taylor
et al., 1999), the maker of Roundup, suggests that
RoundupReady soybeans contain the same amounts of isoflavones
that conventional soybeans do.
Who is right?
The definitive study has not been done, but a comparison
of available results reveals only small differences.
The following table shows the results for two important
isoflavones tested in three different experiments. A
detailed explanation is given beneath the table. These
results should be interpreted cautiously. Because environmental
conditions vary from place to place and from year to
year, soybeans grown at different locations in different
years are likely to contain different amounts of nutrients
due to natural conditions. In many cases it will not
be possible to attribute changing levels of nutrients
to introduced genes or to treatments during the growing
||1992 Padgette study
plants not sprayed
|1993 Taylor study
RR plants sprayed
|late 1990s Lappé study
RR plants may have been
sprayed with Roundup
|RR vs. stndrd
|spread low to high
|RR vs. stndrd
|spread low to high
of the table: For each important isoflavone, the
first line in the table shows the average amount present
in a conventional cultivar and in the genetically engineered
"twin" containing the RoundupReady (RR) trait.
The second line in the table, shaded green, shows how
much the RoundupReady cultivar differed from the conventional
cultivar. A value of -3 indicates that the RoundupReady
cultivar averaged 3 micrograms less of the isoflavone
than the conventional cultivar, while a value of +61
indicates that the RoundupReady cultivar averaged 61
micrograms more of the isoflavone. The table shows that
the RoundupReady cultivar had higher levels of isoflavone
in some experiments and lower levels in other experiments.
The third line in the table shows the lowest and highest
values of isoflavone measured in the crop in that experiment.
The fourth line, shaded in green, shows the numerical
spread from high to low values, calculated by subtracting
the low value from the high value in the third line.
A comparison of the second line with the fourth line
gives an idea of how much the conventional and RoundupReady
cultivars vary in the context of how much the individual
plants of each cultivar vary from one another.
of the two experiments done by Monsanto in 1992 and
1993 is an example of the kind of variation in isoflavone
levels that can occur from year to year. Monsanto used
the same conventional and RoundupReady varieties in
both years. Both varieties had lower levels of genistein
and daidzein in 1993 than in 1992. This is not an unusual
result. Wine afficionados know that the weather can
influence the quality of grapes, causing "good"
years and "bad" years for wine.
did not spray the RoundupReady soybeans in 1992 and
found essentially the same levels of isoflavones in
the conventional and RoundupReady lines. In the context
of results that varied by about 1,000 micrograms from
low to high values, an average drop of 3 or 13 micrograms
is essentially zero change. However this experiment
did not show how much isoflavone the RoundupReady plants
would produce when they were grown under the intended
conditions, that is, when they were sprayed with Roundup.
did spray the RoundupReady plants in 1993 and saw a
small increase in the level of both important isoflavones
in the sprayed plants. As in 1992, the isoflavone levels
vary over nearly 1,000 micrograms from lowest sample
to highest sample in each cultivar, so average increases
of 57 and 61 micrograms in the RoundupReady seeds are
quite small in relation to the variation normally seen
from sample to sample.
experiments, the conventional and genetically engineered
cultivars were grown side by side in the field, so the
plants received very nearly the same conditions of irrigation
and weather. This is what researchers try to achieve
when they compare the results from two cultivars.
done by Lappé et al. also compared a conventional
cultivar with its genetically engineered "twin,"
but did not compare cultivars grown side by side in
the same field. The seeds were ordered from a commercial
seed provider and may have been grown by different farmers.
The researchers assumed, although they did not know
for certain, that the RoundupReady plants had been sprayed
with Roundup during seed production, thus providing
a test of how Roundup application affects the isoflavone
levels in the seeds. The experiments done by Lappé
et al. tested two different pairs of cultivars, while
the Monsanto experiments tested only one pair.
The Lappé study found a much smaller variation
in isoflavone levels from sample to sample than the
Monsanto studies showed. The Lappé study found
reduced levels of both isoflavones in the RoundupReady
cultivars. The reductions for genistein are more extreme
than the changes found by the Monsanto studies, but
these reductions did not exceed the range of variation
in either cultivar. Additional comments by Lappé
and his co-workers on their results and Monsanto's results
are available at http://www.biotech-info.net/cetos_response.html.
The USDA and the University of Missouri (Duke
et al., 2003) also studied the levels of diadzein
and genistein in RoundupReady soybeans that were sprayed
with Roundup, sprayed with other herbicides, or weeded
by hand. For one soybean cultivar in Mississippi, soybeans
that were sprayed twice with Roundup had higher levels
of diadzein than soybeans that were weeded by hand.
The row showing the different levels of diadzein found
in these treatments is highlighted in the table below.
The amounts shown are in micrograms of isoflavone per
gram of plant tissue. The levels of genistein showed
no differences. A second soybean cultivar in Missouri
showed no differences in levels of diadzein or genistein
between plants sprayed with Roundup or weeded by hand.
However, there may be questions about whether these
results settle the issue. In both locations, the hand-weeded
plants showed traces of Roundup, probably the result
of spray drifting from nearby plots. Ideally, the hand-weeded
plots would be entirely free from the treatment that
is being tested.
|cultivar and isoflavone
||sprayed twice with Roundup, at 3
weeks and at 6 weeks
||sprayed once with Roundup at 6 weeks,
two other herbicides also applied
||sprayed once with Roundup at 8 weeks,
two other herbicides also applied
||sprayed with five other herbicides
but not with Roundup
||weeded by hand, no herbicides applied
|DP5806 in Mississippi
Another study involving herbicide use on beans is often
cited as evidence that Roundup may affect the level
of isoflavones in seeds. This study (Sandermann
and Wellmann, 1988) was done on Phaseolus vulgaris
(string beans or kidney beans), a different species
from soybeans, which are Glycine max. The beans
were not genetically engineered to be tolerant to Roundup.
Indeed, no RoundupReady plants were available commercially
in 1988. Few details of the experiment were provided,
but Sandermann and Wellmann appear to have sprayed the
plants with Roundup and then measured isoflavones before
the plants died. They reported that they found increased
levels of isoflavones in all plant tissues, "leaves
as well as fruit", that were exposed to Roundup.
They did not show data comparing the isoflavone levels
of treated and untreated plants. While interesting as
an indicator of issues that warrant further investigation,
the Sandermann and Wellman study is not useful as evidence
of what actually occurs in RoundupReady soybeans.
completed so far seem to indicate that isoflavone levels
in soybeans change in response to several factors. The
application of Roundup may have an effect, but it is
unclear whether the resulting change is an increase
or a decrease in isoflavone levels. The magnitude of
the change appears to be small or moderate in comparison
with natural variation in isoflavone levels. Because
isoflavones may be an important component in the effort
to prevent disease via diet, further research on therapeutic
levels of isoflavones in the human diet, the levels
of isoflavones in soybeans, and the effect of Roundup
on these levels is warranted. Additional evidence may
clarify the arguments for and against Roundup applications
as a risk factor in soybean cultivation.
Other than the issue of isoflavone levels, the nutritional
value of RoundupReady soybeans seem to be the same as
that of conventional soybeans. Experiments with rats,
chickens, catfish and dairy cows (Hammond
et al., 1996) indicate that animals eat the same
amount of food and gain weight whether the soybean diet
is conventional or transgenic. This is important information
because many farmers use soybeans as a source of protein
for their animals.
submitted in support of applications for permission
to sell transgenic crops indicate that the nutritional
components that are commonly tested are similar in transgenic
foods and conventional foods.
For criticism of the research that has been done thus
far on the nutritional value of transgenic foods, see
the article by Arpad Pusztai, one of the figures in
a controversial episode concerning the nutritional value
of GM potatoes (http://www.actionbioscience.org/biotech/pusztai.html).