The scientific substantiation of health claims must be based on a systematic and objective compilation of all available scientific evidence, according to the International Alliance of Dietary/Food Supplement Associations (IADSA).

Providing its comments on the Proposed Draft Recommendations on the Scientific Basis of Health Claims for the Codex Nutrition Committee meeting in South Africa next month, IADSA said while it welcomed a number of revisions in the draft, the priority given to human intervention studies was in need of significant revision.

The text—which has been revised since it was sent back to the drawing board last year following concerns about the structure of the document and the weight given to the different types of evidence required for scientific substantiation—states that short-term human intervention studies in healthy subjects should be the prime source of evidence in claims substantiation.

However, IADSA argues that the proposed draft must take into account all sources of evidence in support of a claim, and that while short-term human intervention studies in healthy subjects are important, they are often not practical for food products and therefore should not automatically be taken as primary sources of evidence.

“Much of what is already known about diet and human health and many existing health claims cannot be validated using gold-standard human intervention studies,” said Professor David Richardson, scientific adviser to the UK Council for Responsible Nutrition and IADSA. “The clinical trial model is only one source of scientific data and is not practical when applied to the reduction of risk of disease in persons generally regarded as ‘healthy’.”

“The relationship between a food constituent and a claimed beneficial effect can be demonstrated by a number of different types of studies and designs,” he continued. “The evidence-based approach needs to include the different sources and nature of the evidence, and take into account all relevant studies including human intervention studies, human observational studies, animal studies and in vitro studies, as well as other pertinent evidence from consensus reports, evidence-based dietary guidelines and history of use.”

IADSA has acknowledged that human intervention studies could provide the most persuasive evidence of efficacy in human subjects. However, it argues that the lack of well-designed randomised controlled trials should not disqualify a body of substantiating evidence from other sources, giving the example that decisions on disease risk reduction would need to draw on a much broader spectrum of evidence, including epidemiological evidence (the study of factors that affect health and illness in populations).

Mr. Richardson also said: “All research approaches, and indeed all studies, are accompanied by inherent limitations, and although reference can be made to a hierarchy of study designs, the relationship between a food constituent and a health outcome can be demonstrated by a number of different types of studies. Each kind of study provides a different kind of evidence.”

He added: “It is not only important to assess the totality of the available data but also to assess the strength of the evidence and level of proof needed to support a health claim. The weighing of the evidence into four grades, such as ‘convincing, probable, possible and insufficient’ is important to stimulate scientific enterprise and level of investment in research so that scientific knowledge of the relationships between foods and food components and health can advance.”