GM crops, unlike conventionally bred crops, are tested exhaustively by looking for any hazards associated with the parent crop, the new gene, the gene product and the new plant variety. Any differences from the conventional variety from which the GM crop was bred are studied in detail and a full health and safety assessment made. Before they can be sold for human consumption, they must be approved by expert regulatory bodies; in the UK this is the Advisory Committee for Novel Foods and Processes and in the EU the European Food Safety Authority.
Thus, all GM human foods and animal feeds must be approved before being offered for sale. All the food safety expert bodies in the developed countries – all, of them, not just some of them – are agreed that approved GM foods are safe to east. In the UK the British Medical Association and the Royal Society agree with that assessment; similar prestigious bodies do so in many other countries.
In consequence, GM foods are judged at least as safe and nutritious as their non-GM counterparts (“at least as safe” because they have been extensively tested which conventional and other foods have not). The majority of them are currently not specifically designed for health benefits, but in some well-defined cases the genetic modification will introduce medicinal or nutritional benefits. In such cases, they might be targeted for specific populations suffering from nutritional deficiencies, like the GM rice and potatoes being developed in SE Asia to combat malnutrition, vitamin and iron deficiency. These are unlikely to be used in the Western World as those conditions are much less common and we have access to other medicines or technologies to overcome them.
Current GM foods in the UK will be indistinguishable from non-GM foods except by very sensitive and specific tests able to detect the actual genetic modification, rather like DNA fingerprinting.
The introduction of GM food crops is not very different from the introduction of any new food variety, and remember that new crop breeds are being produced all the time by traditional means. In conventional crop breeding we know little of what genetic changes have taken place. The new varieties of potatoes you buy from the supermarket are developed by a random mixing of genes.
All new seed varieties, whether GM or conventionally bred, pass through DUS tests. New varieties must be Distinct from other varieties on the market, plants within a variety must be Uniform and the variety must be genetically Stable.
In a GM crop the genetic modification is very precisely defined so making it easier than with conventional breeding to be alert to potential problems. One cannot say that there will be never be negative side effects or drawbacks (nor can one say that about conventionally bred varieties), but GM crops are tested so extensively before being approved that the chances of anything untoward showing up are very small indeed. The chances are likely to be much less than for conventional crops, which undergo few or no comparable safety tests.
There is no evidence whatsoever for GM foods being dangerous to your health. In Canada and the US, hundreds of millions of people have been eating GM foods for around ten years. Maize, soybeans and oilseed rape are commodity crops that, in North America, are not separated into GM and GM-free batches so that products made with either are likely to contain GM ingredients. Soybeans are present in about 60% of processed foods, with maize common in breakfast foods and many others. In all that time there has not been a single confirmed instance of an undesirable health effect with an approved GM product. As one American put it, "Thirteen years of experience with biotech products in the U.S. have shown us that biotech foods developed and used in the U.S. present no safety risk beyond those of their 'natural' counterparts. Not a single ailment has been attributed to biotech foods. Not one. “Not a sneeze, not a rash, not a headache."
Remember that absolute safety cannot be guaranteed for anything, including the food we eat now. Every day our newspapers tell us to be careful about how much we eat (or drink) of one sort of food or another because of medical consequences that might show up years or decades hence. Is any food absolutely safe?
The best question to ask about GM foods is whether they are as safe as the conventional foods from which they came. The answer, after years of experience, is unequivocally "yes".
L. Donaldson and R. May (1999). Health Implications of Genetically Modified Foods. (http://www.doh.gov.uk/pub/docs/doh/gmannex.pdf)
V. Moses and M. Brannan (2001). One hundred percent safe? GM foods in the UK. CropGen (click to download)
Editorial. The Luddites are Coming! The Luddites are Coming! - Those Who Are Blind To The Fruits Of Progress. San Diego Union-Tribune, June 22, 2001 (http://www.agbioworld.org/newsletter_wm/index.php?caseid=archive&newsid=1098)