Sir

We would like to respond to last week's Commentary1 in which Millstone et al. incorrectly assert that: “Substantial equivalence is a pseudo-scientific concept because it is a commercial and political judgement masquerading as if it were scientific. It is, moreover, inherently anti-scientific because it was created primarily to provide an excuse for not requiring biochemical or toxicological tests.”

The concept of substantial equivalence was developed proactively before any new genetically modified (GM) foods came to the market. It was first described in an OECD (Organization for Economic Co-operation and Development) publication in 19932,3 produced by about 60 experts from 19 OECD countries, who spent more than two years discussing how to assess the safety of GM foods. Most of these experts, all nominated by governments, were regulatory scientists from government agencies and ministries responsible for consumer safety.

In 1996, participants at an expert World Health Organization/Food and Agriculture Organization consultation4 recommended that “safety assessment based upon the concept of substantial equivalence be applied in establishing the safety of foods and food components derived from genetically modified organisms”. This represented an endorsement by experts based on three years' experience in the safety assessment of various GM foods.

Substantial equivalence is not a substitute for a safety assessment. It is a guiding principle which is a useful tool for regulatory scientists engaged in safety assessments. It stresses that an assessment should show that a GM variety is as safe as its traditional counterparts. In this approach, differences may be identified for further scrutiny, which can involve nutritional, toxicological and immunological testing. The approach allows regulators to focus on the differences in a new variety and therefore on safety concerns of critical importance. Biochemical and toxicological tests are certainly not precluded.

Since the concept of substantial equivalence was first described, several new foods have been assessed and knowledge has accumulated on how to use the concept. In parallel, the OECD, its governments and others have continued to review its adequacy in food safety assessment and to develop supporting tools5. The OECD's task force on the safety of novel foods and feeds (chaired by P. M.), in particular, continues to focus on the application of the concept. This includes work on assessment methodologies when substantial equivalence cannot be applied, as well as efforts to identify the critical nutrients and toxicants found in major crop plants, as a focus for the demonstration of substantial equivalence.

More than a decade of work by the OECD and its member governments was recognized by the heads of state and government of the G8 countries when they met in June in Cologne and invited the OECD task force to undertake a study of the implications of biotechnology and other aspects of food safety. This additional challenge is certain to lead to further reflections on the concept of substantial equivalence.