The information provided below is based on a position paper published this month in the Journal of the American Dietetic Association (ADA).
To read our article on ‘Functional foods: What they mean around the world’ click here.To read our article on 'Regulation and health claims for functional foods' click here.To read our article on ‘FDA still reviewing functional food regulatory requirements’ click here.
Strength of evidence
Research used to determine the level of evidence behind a diet-disease relationship can range from ‘soft’ to ‘hard’ science, explains ADA.
Studies can be conducted in vitro (in a test tube) or in vivo (in the living). In vivo studies can be conducted either in animals or in humans.
Human studies can be further subdivided into: Subjective sensory evaluations; epidemiologic studies; migration studies; observational; cohort studies; and randomized, placebo- controlled clinical trials, which are considered to be the ‘gold standard’.
“All studies are strengthened by including a control, using a single- or double-blind or cross-over design, and validating the bioactive being tested or evaluation tool being utilized. A meta-analysis is conducted when smaller studies are pooled to increase their statistical power,” writes ADA.
“However, sometimes only certain studies in a meta-analysis meet the qualifying criteria and not all studies are homogeneous in treatment or measurable outcomes. Ultimately, the weight of the evidence obtained through literature reviews should be based on a sufficient number of clinical trials. This information is then used to make claims communicating the functional food’s benefit to consumers.”
Reporting standards
The position paper goes on to explain that another way to pool results of multiple studies is when researchers ensure that a standard check list of information is reported.
This kind of information could include data on the study subjects, use of a control and dosage forms, standardized source of the compounds tested, and frequency.
“Measurable outcomes must also relate to the hypotheses proposed in the study design when evaluating the efficacy of functional foods. This is necessary to safeguard the scientific advancement of complementary and alternative medicine,” writes ADA.
The group goes on to say that where possible, researchers should choose well-defined bioactives, biomarkers or clinical endpoints to evaluate their hypotheses. However, it points out that it is not always feasible to evaluate all measurable outcomes due to financial constraints that limit the type and amount of data collection.
“Another problem facing evidenced based research in the substantiation of a functional food claim is that clear cause and effect relationships are not always easily deciphered in the complex web of individual variability and human physiology.”
“Differences among population subgroups further complicate the identification of clear cause and effect relationships. Increasingly, evidence for functional foods is based on well-designed clinical trials.”