8 April 1999 Genetically Modified Foods: let's be realistic

Many people are fearful about the introduction of genetically modified foods. They are concerned that these new foods will contain new pieces of genetic material that would otherwise not be found in that food. These extra pieces of DNA have been added to foods in order to improve the quality of the food. The best example of the benefit of this technology is the improved resistance to pests of a vegetable crop. This yields two positive outcomes, the food material will contain less pesticide residues and production will be increased. To improve the pesticide resistance of a particular vegetable an additional piece of DNA is added which contains the code for the plant to make a new protein or perhaps a group of proteins. It should be remembered that the basic units of DNA are the same throughout the animal and plant kingdom, it is the sequence of bases in the DNA that produces different enzymes and proteins.

Cross-breeding between plants has, for centuries, been a standard way of exchanging genetic material to give desired features and this has led to significant improvements in the quality and yield of food plants. Genetic modification is much more precise as particular genes are inserted into the genetic material of a plant to achieve particular improvements in the plant. Many of the improvements now being made with genetically modified plants could probably be achieved by traditional cross breeding methods but it would take much longer. Traditional cross breeding involves the exchange of a greater proportion of the genetic material which leads to more uncertain outcomes. Will the new plants be better or worse than the parent plants? Plant breeders have to continue cross breeding for many years to achieve their aim of improving the characteristics of a plant.

The real question to ask is will this additional piece of DNA and protein now found in this new plant have any effect on the consumer? In all the discussions about genetically modified foods nobody appears to have mentioned that the human digestive tract is extremely efficient at degrading the food we eat. Any food that is not digested is very efficiently disposed of in the faeces. In the digestive tract most of the protein and DNA in food are broken down to their smallest components. Proteins are degraded to amino acids and absorbed. The long chain of DNA is broken down into bases, the simplest units of the structure, and also absorbed. These basic units are the same whatever the food we eat. Once the protein and DNA have been degraded they cannot function in the way they did in the food and therefore cannot pose any threat to the consumer. If some of the protein or DNA in our food is not completely digested then they will be voided in the faeces. There is no evidence to suggest that the additional DNA or the proteins made in genetically modified plants are treated in a different way to the material normally found in the food.

The role of new proteins is to facilitate the production of chemicals that are advantageous to the plant e.g. pest toxins. Many plants naturally manufacture a range of chemicals some of these are designed to be toxic to various pests that would otherwise eat the plant to the ground. Thus the real issue is not how the food plant has been modified (to meet the consumer’s needs) but whether new food plants derived by any means have been tested to ensure that they are safe for human consumption. A closer inspection of the foods that we now eat and consider to be safe may yield some interesting results. It would be wiser to spend more time and energy making sure that all our food is wholesome and safe to eat rather than being diverted into an unproductive discussion on the methods used to modify foods.

Dr Geoffrey Savage is a food biochemist and a Senior Lecturer in Biochemistry in the Animal & Food Sciences Division at Lincoln University.

Dr Geoffrey Savage, Animal & Food Sciences Division, Lincoln University, Canterbury, New Zealand