Companion Publication Biotechnology
and Sustainable Development
Chapter 3
Agricultural
Biotechnology, Food Safety and Human Health
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The
applications of modern biotechnology to agriculture, particularly the
development of genetically modified foods and other living modified organisms (LMOs),
are the subject of widespread public debate as to the safety and efficacy of the
new products, and the ethical and socio-economic issues surrounding their
development and use. Public concerns about gene technology lie in four major
areas:
·
Ethical issues
·
Socio-economic effects
·
Food safety and human
health,
·
Impact on biodiversity
and the environment.
This chapter deals with
the scientific issues associated with assessing the risks and benefits of
genetically modified foods to human health.
Risks to Human Health
There
are several areas of public concern in regard to potential human health risks of
genetically modified (GM) foods. These concerns relate to understanding the
potential of proteins and/or other molecules in GM foods to cause allergic
reactions, to act as toxins or carcinogens, and/or to cause food intolerance
reactions. Other concerns relate to the use of antibiotic-resistant makers in
crops and the potential for their transfer to human pathogens. There are also
concerns about possible unintended effects of gene technology.
The risks to be
assessed include the need to be aware of possible unintended effects of all new
foods, including those produced by the applications of gene technology. The
possible unintended consequences of gene technology and the risks that these
represent in GM foods include unanticipated compositional changes in food. Such
effects are known to occur occasionally in conventional plant breeding, and may
also occur during biotechnology-based crop improvement.
Methods
to test and evaluate these types of risks are being applied to GM foods to
detect any increased risks associated with particular foods.
These methodologies are kept
under continuing review and updating through a series of consultations organized
by the Food and Agriculture Organization (FAO) and the World Health
Organization. The 2000 consultation (FAO/WHO 2000) concluded that the
Consultation was satisfied with the approach used to assess the safety of the
genetically modified foods that have been approved for commercial use.
There are no instances known of harmful
effects on human health resulting from the consumption of presently available GM
foods (OECD 2000). However, this does not mean that risks do not exist as new
foods are developed with novel characteristics. GM foods need to be assessed on
a case-by-case basis, using scientifically robust techniques, to ensure that
those foods that are brought to market are safe for consumers.
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Benefits to Human Health
The
risks in genetically modified foods need to be weighed against the benefits.
Future genetically modified foods that are being developed include a number of functional
foods that may offer some nutritional benefits to consumers in both
industrial and developing countries. Human health benefits of genetically
modified foods lie in the potential for introducing traits that convey factors
such as:
·
Improved nutritional
quality of foods (eg higher vitamin and mineral content, lower fat content)
·
Reduced toxic compounds
in food (eg cassava with lower levels of cyanide)
·
Pest tolerant crops able
to be grown with lower levels of chemical pesticides
·
Disease resistant crops
with lower levels of potentially carcinogenic mycotoxins.
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The Scientific Basis of Risk
Assessment of Genetically Modified Foods
Several international scientific unions
have undertaken a joint review of the scientific basis for assessing the risks
and benefits of genetically modified foods and crops, in relation to their
impact on human health and nutrition. The findings of this study in regard to
the scientific basis of regulation and risk assessment are summarised here,
based on the review by Kuiper (2002).
Safety assessment of GM foods is carried
out on a case-by-case basis, taking the specific genetic modifications into
account, and comparing the properties of the new food with those of the
traditional counterpart. This comparative approach, applying the principle of substantial
equivalence, is based on the assumption that conventional foods are
generally considered as safe for consumption, based on a history of safe use.
Any identified differences between the GM food and its conventional counterpart
are assessed with respect to their safety and nutritional implications for the
consumer. The concept of substantial equivalence,
as developed by the OECD and endorsed by the United Nations Food and
Agricultural Organization and the World Health Organization, is a starting point
for safety evaluation and contributes to an adequate food safety assessment
strategy. Thus, substantial equivalence is a conclusion that may be reached
after comparative analysis of a genetically modified food and its traditional
counterpart. If no significant differences are detected, a conclusion of
substantial equivalence is reached. If significant differences are identified,
they are used to highlight areas for further examination to see if there are any
food safety concerns that need to be addressed.
The comparative safety assessment
approach should be followed for the next generation of GM foods in order to
establish the degree of equivalence with presently available foods. The
unmodified host organism may function as the relevant comparison for testing the
degree of equivalence, but in some instances a safety assessment of the new food
per se will be necessary. The latter may be required for GM crops
with extensive modification of existing metabolic pathways or addition of new
ones, or for GM plants with decreased levels of naturally occurring toxins,
which previously could not be used as food sources. Food safety assessment
strategies should be designed on a case-by-case basis (Kuiper 2002). Guidelines
for the safety assessments of foods derived from recombinant DNA plants have
been developed by FAO/Codex (FAO 2002).
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New
methods for safety assessment of whole foods
Safety testing of whole foods is
difficult. New approaches for safety assessment of whole foods, taking advantage
of modern molecular, biological, toxicological and analytical methods, are
possible. Present approaches for detecting expected and unexpected changes in
the composition of GM food crops are primarily based on measurements of a
limited selection of single compounds (targeted
approach). In order to increase the
possibility of detecting any unintended effects, new profiling methods (using
gene expression technologies, proteomics and metabolomics) should be further
developed and validated, for a non-targeted
approach.
Such new profiling techniques should
enable increasingly comprehensive assessments of compositional changes in food.
The principal problems associated with advanced technologies for the
determination of compositional changes in food lie not in the compositional
analyses themselves, but in assessing the significance of the results of those
analyses (Kuiper 2002).
New approaches to food safety testing are
of particular interest for assessing the safety and nutritional significance of
future GM foods and crops that are being developed for potential improvements in
their nutritional qualities, such as increased vitamin or mineral content or
modified oil content.
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Post
market monitoring of foods
The usefulness of post-marketing
surveillance as an instrument to gain additional information on long-term
effects of foods or food ingredients, either GMO-derived or traditional, should
not be overestimated, given the multifactorial origin of many food-related
diseases and the variability in genetic predisposition of the human population.
Routine application in the food sector may yield limited information, and
would be costly. Only in cases with specific biological end-points, for
example identifying allergenicity or food intolerance, or when exposure
assessment is hampered by insufficient insight into the diets of specific
consumer groups, do post-marketing surveillance strategies seem to be useful.
Pre-market safety assessment of GM foods will need to provide sufficient safety
assurance for consumers (Kuiper, 2002).
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Assessing
Risks of Allergenic Reactions from GM foods
Allergenicity may
be raised in foods by raising the
level of a naturally occurring (endogenous) allergen or by introducing a new
allergen. Any protein that has been added to a food should be assessed for its
potential allergenicity, whether it is
added by genetic engineering techniques or by other manufacturing processes.
More than 90 percent of the food allergens that occur in 2 percent of adults and
4 to 6 percent of children are associated with eight food groups, particularly
crustacea, eggs, fish, peanuts, soybean, tree nuts and wheat. These foods merit
close attention when examining GM foods for the potential for any increased risk
of allergenicity (Lehrer 2000).
Genetic modification
may alter the allergenicity of a food by different ways. First, the level of
naturally occurring (endogenous) proteins within a particular crop may be
altered by genetic manipulation, potentially raising the level of endogenous
allergens. Second, the expression of a new gene in the crop could introduce new
allergens normally not present in this particular crop. Thus, there can be an
effect on known allergens or unknown allergens. If the endogenous proteins or
the newly introduced protein are from known sources of allergens, then assessing
the allergens within the GM food is relatively straightforward. A more difficult
issue is if the allergenicity of the source of the protein is unknown. This
relates only to new proteins being introduced into GM foods from sources that
have ordinarily not been used as human food. The dilemma is that there is no
available body of knowledge about the allergenicity of these proteins, and thus
the need to rely on other criteria with which to assess their potential activity
(Lehrer 2000).
Gene technology may
also be used to decrease the allergenicity of certain foods, by deleting the
genes that encode for certain known allergens. This approach is being tried in
peanut, for example, so as to decrease the risk associated with peanut
consumption.
A Panel convened by the
International Life Sciences Institute (ILSI) Allergy and Immunology Institute
and the International Food Biotechnology Council (IFBC) developed scientific
approaches to assess the allergic potential of foods derived from GM crop
plants. Their report (Metcalfe et al 1996) addressed the cell biology, symptoms
and treatment of food allergy; developed a catalog of allergenic foods; and
characterized major food allergens from the perspectives of the methods used to
genetically modify food crops. The Panel also developed a decision tree to
provide a framework for assessing the allergic potential of foods derived from
genetically modified plants. The
decision tree used the following risk assessment criteria:
That an introduced protein in a food is not
a concern if there is: (1) no history of common allergenicity, (2) no similar
amino acid sequence to known allergens, (3) rapid digestion of the protein, and
(4) the protein is expressed at low levels.
Genes transferred from
sources known to be allergenic should be assumed to encode for that allergen,
until proven otherwise. This transfer of allergenicity was demonstrated when a
gene was transferred experimentally from Brazil nut to soybean, with the
intention of enhancing production of sulfur-containing amino acids in soybean (Box
3.1).
In the Joint FAO/WHO 2000
consultation on safety aspects of
genetically modified foods of plant
origin, the issue of the allergenicity of genetically modified foods was
addressed. The IFBC/ILSI decision-tree approach was adapted for the evaluation
of novel proteins introduced into genetically modified foods (Figure
3.1). The
Consultation concluded that if a
genetically modified food contains the product of a gene from a source with
known allergenic effects, the gene product should be assumed to be allergenic
unless proven otherwise. The transfer of genes from commonly allergenic foods
should be discouraged unless it can be documented that the gene transferred does
not code for an allergen(FAO/WHO 2000).
The FAO/WHO 2000
Consultation also concluded that additional criteria should be considered when
the source of the genetic material is not known to be allergenic. The level and
site of expression of the novel protein and the functional properties of the
novel protein are two such criteria.
The FAO/WHO 2001
Consultation developed a new decision tree (Figure
3.2) that builds upon
previous approaches to examining allergenicity but also encompasses several
additional strategies. In contrast to previous decision-tree strategies, the FAO/WHO
2001 decision tree makes no distinction between commonly and less commonly
allergenic source materials with respect to specific serum screening. Thus,
specific serum screening is undertaken irrespective of the relative frequency of
allergy to the source material in question, provided sera are available.
The
2001 Consultation accepted that the current decision tree (Figure
3.2) will
require future modifications as a result of the rapidly expanding scientific
base in the allergy and biotechnology fields, but concluded that this decision
tree is appropriate now, based on present knowledge. One issue for future
consideration is the potential risk associated with inhaling (as distinct from
ingesting) allergens from GM crops.
The
major challenge is testing the source of the gene from which there is no history
of allergenic activity, since there are theoretically no known sera available
from allergic subjects to test the product. The presently recommended approach
is to compare the amino acid sequence of the protein with that of known
allergens. Any sequence similarity with a particular allergen suggests the sera
can be used to screen the product by immunochemical procedures. If there is no
amino acid sequence homology, the stability of the protein to enzymatic
digestion and processing can be assessed. If the molecule is easily digested or
unstable then the risk of allergenicity is low and there should not be a problem
with marketing the product. If, however, the molecule is stable to digestion and
processing, then regulatory authorities need to consider the risks it may pose
to some members of the population as a source of possible allergens (Lehrer
2000).
For genetically
modified foods entering the marketplace, consumers should be informed by
appropriate labeling if the food contains known or suspected allergens, as is
the case with other common foods containing nuts or other known allergens
(Metcalfe et al 1996).
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Assessing Risks of Antibiotic
Resistance Transfer from GM foods
There are public
concerns about the risk that the antibiotic-resistance genes used as selectable
markers in developing genetically modified foods may be transferred to
microorganisms that are human pathogens, adding to the increasing problem of
antibiotic resistance in human pathogens. This problem of decreasing
effectiveness of antibiotics has arisen largely as a result of widespread
overuse of antibiotics in human and animal health. However it is highly unlikely
that the use of antibiotic markers in GM foods is a component of the problem.
Studies by the OECD, FAO and WHO have assessed the risk of transfer of an
antibiotic marker from a GM food to a human pathogen as being remote. (FAO/WHO,
2000). This would entail the horizontal transfer of a gene across widely
dispersed species, a rare event. Nevertheless, the use of these antibiotic
markers as selectable markers in GM foods is being phased out.
Selectable marker genes
are required to ensure the efficient genetic modification of crops. Selectable
markers used to identify transformed plants in the development phase confer
resistance either to antibiotics, herbicide or metabolic inhibitors. Once the
transformed plants have been identified, these markers are no longer required.
Several strategies (site specific recombination, homologous recombination,
transposition, and co-transformation) have been developed to eliminate these
genes from the genome after they have fulfilled their purpose. Chemically
inducible, site-specific recombinase systems are also emerging as valuable tools
for efficiently regulating the excision of marker transgenes when their
expression is no longer required (Hare and Chau 2002).
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Labeling of Genetically Modified Foods
A key concern of some
consumers is being able to identify those foods that may contain allergens and
other potentially harmful substances, so that people who have allergic or food
intolerant reactions to particular foods can avoid them. Others may wish to
avoid certain foods on health, ethical or religious grounds. Informative food
labeling could provide information about the composition of specific products
and enable consumers to make choices about their use, after assessing their
risks and potential beneficial effects.
Informative
labeling of GM foods requires that the nutrient content of the food is
disclosed, in relation to similar foods produced by conventional techniques of
crop improvement and cultivation, as well as any additional protein (or other)
content resulting from the specific transgene modification. Labeling of food as GM
or non GM indicates the use of modern molecular plant breeding and
other production techniques involving gene technology. It conveys no information
to consumers as to the nutritional content or safety of particular foods.
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Food Safety Standards
One
result of public concerns about the safety of GM foods is that GM foods are now
required to meet higher standards of safety than foods produced either by
conventional agriculture or by organic agriculture.
Given increasing global concerns about
food safety broadly, all countries need to have in place food safety regulations
and human and institutional capacity to be able to set and apply food safety
standards. Food safety standards are required to ensure the quality of food
supplies both for local consumption in the country of origin and to meet
increasingly stringent export standards set by importing countries. Achieving
internationally agreed food safety standards for GM foods that guarantee safety
of products, and are not perceived to be non-tariff barriers to trade is a
challenge to the international community.
Further
information and references
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Go to Chapter 4 -
Agricultural Biotechnology, Biodiversity and the Environment
New Genetics, Food &
Agriculture: Scientific Discoveries - Societal Dilemmas