1 October 2002 | EN | 中文
Substantial progress has been made to increase the yields of the major cereal crops to feed the world's poor and to alleviate hunger. But while general nutrition has been greatly improved through increases in the intake of calories, the availability of micronutrients (including vitamins and certain minerals) remains a serious problem for many in the developing world. GM technology has already been used to produce crops in greater quantity and of better quality — does it also offer a promising avenue to nutritionally enhance food?
Since the start of the Green Revolution in the 1960s, substantial progress has been made to increase the yields of the major cereal crops — rice, wheat, and maize — to feed the world's poor and to alleviate hunger.
These developments have led to significant improvements in food security, mainly in terms of basic energy needs. However, while general nutrition has been greatly enhanced through increases in the intake of calories, the availability of micronutrients (including vitamins and certain minerals) remains a serious problem for many in the developing world.
The scientific community first called the world's attention to micronutrient malnutrition (often referred to as "hidden hunger") in the late 1970s and early 1980s. This reflected an awareness that the overt signs of this form of malnutrition — childhood and maternal death, anaemia and goitre — were in fact part of a less defined condition affecting large populations. In the 1980s, it was estimated that two billion people were at risk of iron deficiency anemia, 1.6 billion of iodine deficiency disorders, and more than 250 million young children of vitamin A deficiency.
In 1990, leaders attending the World Summit for Children pledged to protect the world's children from malnutrition. More than a decade later, food fortification (for example, adding iodine to salt) and supplementation programmes have seen some success, but micronutrient malnutrition continues to plague a large proportion of the world's poor.
Several factors are responsible for this trend. A substantial reduction in the price of staple foods has meant they have become more predominant in the diet of poor people. They still cannot afford to buy sufficient quantities of vitamin- and mineral- rich non-staple foods such as vegetables, fruits, pulses, and animal and fish products. Moreover, there is limited public education about nutrition — especially among the resource-poor — leading to an absence of demand for improved food quality. As a result, many people remain undernourished and vulnerable to the health risks associated with a poor diet.
Production of an optimum range of food types required for adequate nutrition remains a problem for subsistence producers in many areas of the world. Furthermore, none of the crops grown today were originally selected to address all our nutritional requirements. Instead, our ancestors chose them intuitively from the edible plants that were growing around them.
One way of enabling the resource-poor to enjoy a more balanced diet is to 'nutritionally enhance' existing food crops. This is possible using a range of techniques, including conventional plant breeding and genetic modification (GM) technology. The latter enables genes encoding desirable traits to be cloned from a living organism and inserted into the target plant.
Progress in nutritionally enhancing crops
GM technology has the potential to make foods in greater quantity and of better quality available to populations that need it most. By improving yields and reducing the need for pesticides, this technology has already made an important contribution to the nutritional needs of the poor, largely in terms of increasing food availability. In recent years, researchers have also explored creating transgenic crops that produce specific dietary molecules, including certain vitamins and fats.
A classic example is so-called Golden Rice, which was developed to help increase the intake of dietary vitamin A. Lack of this vitamin is a major cause of blindness in developing countries — affecting up to 500,000 children a year — and is known to seriously compromise childrens' general health. Genetically engineering rice to produce provitamin A (beta-carotene) has received a lot of attention as a way to tackle this widespread nutritional deficiency.
|Golden Rice was developed by inserting two genes (phytoene synthase and lycopene beta-cyclase) from the daffodil plant, and one gene (phytoene desaturase) from the bacterium Eriwinia uredovora into the rice genome. The products of these genes complete the beta-carotene biosynthetic pathway in the endosperm of the rice grain. A type of japonica rice (Taipei 309) has recently been developed that synthesizes 1.6 mg carotenoid/g dry rice endosperm. |
The discovery of Golden Rice was announced by Swiss scientist Ingo Potrykus in 1999 . Soon after, the biotechnology companies AstraZeneca and Monsanto agreed to waive licensing fees for use of their technologies in developing the crop further for 'humanitarian' purposes. The International Rice Research Institute (IRRI) in the Philippines took up this challenge in January 2001 and has succeeded in transferring the provitamin A trait from the modified japonica rice to an indica background (which is more suitable for cultivation in Asia) using conventional rice breeding. IRRI has subsequently transformed several high yielding indica varieties with genes that enable biosynthesis of beta-carotene.
Given the high consumption of rice in south and south-east Asian countries, rice with added provitamin A could have a significant impact on human nutrition and health, especially in Vitamin A deficient women and children (who are also likely to suffer from anaemia). However, doubts remain over the nutrient's bioavailability — the extent to which the added nutrient is taken up by the body of the person consuming it — in the edible part of the plant.
Questions have also been asked about the stability of the provitamin during storage and post-harvest processing, as well as its thermal stability during cooking. Furthermore, Golden Rice has attracted significant criticism from non-governmental organisations such as GRAIN (see 'Grains of delusion'), who argue that it is a strategy designed for developed countries to avoid direct food aid obligations and to gain acceptance of GM technology 'through the back door'.
GM technology is also being used to enhance provitamin A content in the mustard plant, a relative of canola (oil seed rape) that is grown in many parts of the world, including Bangladesh and India. The transformed mustard seed oil is expected to contain enough beta-carotene to have an impact on alleviating Vitamin A deficiency in these countries. 
Another public/private collaboration — between Monsanto and Michigan State University, together with the US Agency for International Development and the Tata Energy Research Institute in India — has looked at increasing the levels of carotenoids in canola. These micronutrients, found in brightly coloured fruits and vegetables, are thought to help reduce the risk of contracting certain chronic diseases such as cancer. The insertion of genes encoding the enzymes needed to synthesise carotenoids has resulted in a concentration of 1000 to 1500 mg carotenoids per gram of canola seeds. 
Genetic modification has also been used to develop soybeans with increased levels of oleic acid, a mono-unsaturated fatty acid thought to help reduce the risk of heart disease and the accumulation of 'bad' cholesterol. The level of oleic acid soybean oil has been increased from 24 to 80 per cent, making it comparable to that of peanut and olive oils. (5) Beneficial plant-based omega-3 fatty acids have also recently been introduced into oil seeds.
Concerns about nutritionally enhanced foods
The opportunity to improve the nutritional quality of food through GM technology is an exciting one. However a number of concerns exist, not least the possibility that new allergens could be introduced into these crops during the genetic modification process. Potential allergens include the markers (typically antibiotic resistance genes) used during plant transformation, as well as allergens from the source of the foreign genes. Moreover, it is possible that adding to, or altering, a biological pathway could cause an imbalance or 'trade-off' with other components that could be antagonistic to the nutrient being incorporated.
Although these are valid concerns, there is little robust evidence to suggest that GM food poses any greater risk of introducing allergens than new crops developed by traditional methods. Additionally, researchers are now looking at removing the potentially allergenic markers from the end product or using alternative markers. For example, IRRI is now working on transgenic Golden Rice using phosphomannose isomerase (pmi), which is a selectable marker involved in sugar metabolism.
Other groups are actually working on producing 'non-allergenic' GM versions of crops, which can be eaten by those suffering from a relevant food allergy. For example, scientists in Japan have reduced the level of allergenic proteins in rice by 'silencing' the gene that expresses these proteins . Other research groups are working to reduce the allergenicity of peanuts  and wheat .
The advancing fields of human and plant genomics and proteomics will no doubt continue to identify plant-based compounds beneficial to human health if transferred into food crops. In order to be accepted by consumers, however, a cautious approach will be required to ensure that such crops pose no greater health, environmental or economic risks than conventionally produced food. This will be best achieved by a holistic, multidisciplinary approach involving plant scientists, nutritionists, soil scientists, ecologists, economists and policy makers. Such collaborations will help to ensure that new risks associated with GM technology are identified and carefully managed.
Conventional breeding versus GM technology
Genetic modification can enable plant manipulations that are impossible using conventional plant breeding; however the more traditional approaches still have a crucial role to play in nutritionally enhancing food crops. It is important to acknowledge that both approaches can be used together to great effect, with the shortcomings of one being addressed by the potential of the other. Certainly, the value of conventional breeding should not be overlooked.
For example, traditional plant breeding at IRRI has succeeded in producing rice with an 80 per cent increase in iron density , which could be further increased by cross-breeding between different iron-rich genotypes. While GM technology has also been used to insert a ferritin gene into japonica rice  to increase iron levels, it has not given superior results. Moreover, conventional breeding is ultimately required to transfer the ferritin gene from japonica to high-yielding indica rice varieties. It may be true that eventually the most iron-dense genotypes will be developed using GM technology (by incorporating ferritin genes into conventionally bred high iron varieties), but such a strategy has yet to be demonstrated.
A recent development at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in India also illustrates how conventional breeding will continue to play an important role in developing nutritionally enhanced crops. Earlier this year, scientists there announced that they had discovered a natural variety of pearl millet containing high levels of beta-carotene (which they named 'golden millet'). They are now breeding the variety — which was found in ICRISAT's gene bank — to produce high yielding hybrids that can be grown in different parts of the world.
Lessons to consider
The potential application of GM technology in helping to provide more nutritious food crops — especially in developing countries — requires consideration of the following issues:
While these points must be seriously considered, it is important not to be overly cautious. The benefits of nutritional enhancement through GM technology to the poor in developing countries are potentially very significant. The promise of lowered costs of food crops and improved health indicates that research and uptake in this area should be vigorously pursued.
Glenn Gregorio is a scientist at the International Rice Research Institute and is based in Manila, Philippines.
 Beyer P, Al-Babili S, Ye X, Lucca P, Schaub P, Welsch R, and Potrykus I (2002) Golden rice: introducing the beta-carotene biosynthesis pathway into rice endosperm by genetic engineering to defeat vitamin A deficiency. J. Nutr. 32:506S-510S
 Ye X, Al-Babili A, Kloti A, Zhang J, Lucca P, Beyer P, and Potrykus I (2000) Engineering the provitamin A (b-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm. Science 287:303-305
 Dhawan V (2001) Biotechnology and the promise for Control of Vitamin A deficiency. Presented at the 20th meeting of the International Vitamin a Consultative Group, Vietnam, 15 Feb 2001
 Shewmaker CK, Sheehy JA, Daley M, Colburn S, Ke DY (1999) Seed specific overexpression of phytoene syntase: increase in carotenoids and other metabolic effects. Plant Journal 20:401-412
 Facciotti MT, Bertain PB, Yuan L (1999) Improved strearic phenotype in transgenic canola expressing a modified acyl-acyl carrier protein thioesterase. Nature Biotechnology 17:593-597
 Tada Y, Nakase M, Adachi T, Nakamura R, Shimada H, Takahashi M, Fujimura T, MatsudaT (1996) Reduction of 14-16 kDa allergenic proteins in transgenic rice plants by antisense gene. FEBS Letters 391:341-345
 Bannon GA, Shin D, Maleki S, Kopper R, Burks AW (1999) Teriary structure and biophysical properties of a major peanut allergen, implications for the production of hypoallergenic protein. International Archives of Allergy and Immunology 118:315-316
 Buckanan BB, Adamidi C, Lozano RM, Yee BC, Momma M, Kobrehel K, Ermel R, Frick OL (1997) Thioredoxin-linked mitigation of allergic responses to wheat. Proceedings of the National Academies of Science 94:5372-5377
 Gregorio, GB (2002) Progress in Breeding for Trace Minerals in Staple Crops. J. Nutr. 132:500S-502S
 Lucca P, Hurrell P, and Potrykus I (2002) Fighting iron deficiency anemia with iron-rich rice. Journal of the American College of Nutrition 21:184S-190S
All SciDev.Net material is free to reproduce providing that the source and author are appropriately credited. For further details see Creative Commons.