In addition to GM foods themselves, many foods contain GM food additives made from GM microbes.
There are different attitudes in various countries about whether labelling is necessary and how to do it.
Labelling procedures are now in force in the EU and the UK. The European approach considers not what the product is (for example, oil from GM oilseed rape is chemically identical to that from a non-GM source) but how it is made. Current thinking is to apply a label "contains" if the proportion of material of GM origin in any ingredient exceeds 0.9%. The UK government view is that for refined foods like oil this is impracticable because it may be impossible to detect the GM content, and that legislation that cannot be enforced is futile. The British view favours a "GM-free" label for those who wish to use it.
The US attitude is to label a food for what it is, not for how it is made. There is accordingly no mandatory requirement to label a product as GM because the foods approved are as safe and nutritious as the unmodified crops from which they came. The American view is that a label flags up some sort of danger that is simply not true. However, in the US, labels (either "contains" or "does not contain") may be used voluntarily so long as they meet normal requirements: they must be informative, accurate and truthful.
Many British supermarket chains say that their own house brands are free from GM components, but whether this means "totally free" or "substantially free" is not obvious. Non-house brands normally do not make such a claim. Organic foods claim to be entirely free from GM components but are legally bound by the same EU regulations as any other foodstuffs: if the proportion of material of GM origin in any ingredient exceeds 0.9%. The EU regulations give no legal force to a zero content of GM material in organic foods and feeds.
Just as for organic food, there is currently no way of telling by taste or appearance whether what you have eaten is GM, because it is just like conventional food. Unlike organic, the difference may be detectable using very sensitive laboratory methods while “organic” foods show no consistent differences from their conventional counterparts.
Many people from the UK eat GM foods on holiday in the US and elsewhere without worrying about it.
Commissioner David Byrne welcomes political agreement of Council on further labelling requirements for GMOs in food and feed (Commissioner David Byrne welcomes political agreement of Council on further labelling requirements for GMOs in food and feed. EU press release DN: IP/02/1770 (29/11/2002) (http://europa.eu.int/rapid/start/cgi/guesten.ksh?p_action.gettxt=gt&doc=IP/02/1770|0|RAPID&lg=EN)
G. Conko (2002) Eat, Drink, and Merry; Why Mandatory Biotech Food Labeling is Unnecessary. Cascade Policy Institute (http://www.cascadepolicy.org/pdf/env/I_120.pdf)
J. Barnard. (The Associate Press November 6, 2002). Oregon rejects initiative to make state first to label genetically modified foods. (http://www.checkbiotech.org/root/index.cfm?fuseaction=search&search=Oregon&doc_id=4117&start=1&fullsearch=0)
J. M. Bainbridge (2004). Recent developments in the regulatory system in the UK. Journal of Commercial Biotechnology, 10,241-247.
J. Kinderlerer (2004). The regulatory system in the EU and further afield. Journal of Commercial Biotechnology, 10, 248- 257.