The variety of foods consumed by humans has changed greatly over the centuries, altering the balance of nutrients in the diet. Plant breeding by traditional methods, mutations and recombinant DNA technique can be used to alter nutritional quality and functional traits. Thirty years ago, traditional breeding was utilized to identify and select rapeseed plants free of the nutritionally undesirable fatty acid, erucic acid. The resulting plant, canola, produced an oil that has a more desirable fatty acid profile. Canola oil now makes up a significant proportion of the daily lipid intake of the consumers in most of the developed nations of the world. More recently, mutational breeding has been used to genetically modify flax plants to produce edible oils instead of the traditional high linolenic industrial oil. The introduction of new foods and the growing interest in functional foods also have the potential to modify the food supply. The availability of recombinant DNA techniques provides the opportunity to develop foods that help optimize health status. The major difference with recombinant DNA techniques is the ability to introduce different nutrient profiles with greater speed and precision.
Genetic modification of plants now under cultivation have been directed towards agronomic enhancement. Nutritional changes may have a more profound impact on the health of the population. At present, there are no foods derived from genetically modified plants modified to enhance nutrition in the commercial market. However, there are several plants with altered nutrient composition being developed using recombinant DNA technology. These have been designed to modify nutrient composition and levels or change the functionality of a product. An example of the latter is potato tubers containing increased amounts of starch that is distributed more uniformly, resulting in more efficient processing, lower fat absorption and improved texture. It is anticipated that other genetically modified plants will be developed with nutritional characteristics targeting major health problems.
There are a number of examples of genetically modified plants from which foods are produced with the objective of improving health and enhancing food functionality. These include two examples of genetically modified rice varieties, one in which beta-carotene was produced and another in which an undesirable component for sake brewing (glutelin) was decreased. Other examples were oil seeds in which the fatty acid profile was changed either by traditional mutational techniques or recombinant DNA technique. Recently, canola and soy oils with combined low levels of saturated fatty acids and increased oleic acid, have been produced with the objective of lowering total and low density lipoprotein (LDL) cholesterol levels, one of the risk factors for cardiovascular disease, while at the same time enhancing the functionality of the oil. The Consultation heard details of the recently reported golden rice which was specifically designed to target Vitamin A deficiency, a cause of blindness among people living in developing countries (Ye et al., 2000).) These examples highlight the potential of foods with modified nutritional profiles to reduce the incidence of nutrition-related conditions or diseases.
Traditional plant breeding techniques of intra and inter-species crossing and mutation are designed to create genetic variation upon which selection of the most desired genotype is the expected outcome. All plant breeding procedures can produce unexpected effects. Low glutelin genetically modified rice, created using an anti-sense technique, signifies improvements in rice storage proteins for commercial sake brewing. The decrease in glutelin levels was however associated with an unintended increase in levels of prolamins. This illustrated that a targeted change in the level of a specific protein can result in other proteins being affected. The change in prolamin levels did not affect the industrial application but could affect nutritional quality and allergenic potential if the rice were used as a food. Other examples were given regarding soybean and rice showing that genetically modified soy with increased lysine showed an unexpected decrease in oil content, and the genetically modified golden rice designed to express beta-carotene unexpectedly accumulated xanthophylls. The use of tissue-specific promoters was suggested as a means to limit the number and extent of unexpected effects.
In the case of the low glutelin rice, the change in prolamins would not be detected by standard nutritional analyses such as total protein and amino acid profiles. This was only observed following sodium dodecyl sulphate (SDS) gel electrophoresis. The unexpected finding of xanthophylls in the beta-carotene-enhanced genetically modified rice would not have been apparent from standard nutritional analyses. This difference was observed following high pressure liquid chromatography (HPLC) analyses for carotenoids. Thus, it is important that appropriate analyses of nutrients should be carried out to identify unexpected changes.
The ability to change nutrient levels in crop plants through plant breeding, including the use of recombinant DNA techniques, has the potential to result in broad changes in at least two ways: (1) the intended modification in plant constituents could change the overall nutrient profile of the plant product and this change could affect nutritional status of the individual, (2) in addition, unexpected alterations in nutrients could also affect nutrient profiles of the product and nutritional status of people. Although the genetically modified plant components may be assessed as safe individually, the impact of the change on the overall nutrient profile must be determined. Because changes in individual nutrients could affect a number of plant processes and nutritional outcomes, it is recommended that integration of nutritional and toxicological expertise needed for the evaluation of genetically modified foods be encouraged and facilitated. Consideration should be given to assessing the potential health impact resulting from changes in nutrient profile arising from all types of plant breeding.
Examples of the use of mutational breeding to alter the nutritional characteristics of plants include the modification of flaxseed oil from a high linolenic industrial oil to a high linoleic oil similar to corn oil in its fatty acid composition, and genetically modified soy and canola plants being developed that produce a high oleic acid (80-90%) oil that also displays very low levels of saturated and polyunsaturated fatty acids.
It will be important to determine if the overall nutrient profile of a genetically modified food has been changed and if dietary intake patterns are altered by the introduction of foods from genetically modified plants. The introduction of a significant nutritional change in a food may require post-market assessment to determine whether the overall diet has been altered and to what degree, before an assessment of the impact on nutritional status can be made.
It is important to ascertain to what extent the modified nutrient is bioavailable and remains stable with time, processing, and storage. For example, the question was raised as to what extent carotenoids in the genetically modified rice remained stable under storage conditions encountered in the developing countries.
Where additional assurance of safety is sought, analytical methods traditionally applied in the evaluation of food constituents such as total protein, fat, ash, fibre and micronutrients may need to be augmented with additional analyses to identify unexpected effects and altered nutrient profiles and bioavailability which may impact on dietary intake and health.
Because of the potential for broad changes in nutrient levels and interactions with other nutrients and unexpected effects, it may be necessary in certain instances to undertake feeding studies in animals to determine outcomes that result from changes in nutrient profiles and nutrient bioavailability. Nutritional modifications which are within the normal range of nutrient variation might require a less extensive evaluation than those outside normal ranges.
Genetically modified foods have the potential to improve the nutritional status of individuals and provide products with enhanced functionality for populations in developed and developing countries. The major issues relate to possible nutritional imbalances and the introduction of unexpected alterations in nutrients and other compounds. The change in nutrient levels in a particular crop plant may impact overall dietary intake. In such cases, it would be important to monitor changes in nutrient levels and bioavailability in such foods and evaluate their potential effect on nutritional and health status of consumers. However, an assessment of the impact on nutritional status of consumers is important for all significant dietary changes and not specific to the introduction of genetically modified foods.