Two papers published recently highlight the concerns and determination of leading figures in the nutrition arena to define a new paradigm for the testing of nutrients, which includes, but is not exclusive to, data from randomized clinical trials (RCTs).
The literature is littered with examples of randomized clinical trials involving nutrients that failed to live up to expectations. Indeed, epidemiological evidence linking dietary antioxidant intake, for example, and reduced risks of a range of disease is strong, but when such antioxidants have been extracted, purified, or synthesised and put into supplements, the results, according to the RCTs, do not produce the same benefits, and may even be harmful.
In a new commentary in the Natural Medicine Journal, the Council for Responsible Nutrition’s Andrew Shao, PhD, and Duffy MacKay, ND, explain the reliance in scientific circles on evidence from RCTs: “Nutrition researchers have yet to establish clear criteria and guidelines for how best to study the effects of nutrients in humans, and subsequently how to evaluate those findings—in other words, what constitutes evidence-based nutrition (EBN).
“In the absence of such guidelines, the long-established principles of evidence-based medicine (EBM) and its strong reliance on randomized, controlled trials (RCTs) have been applied to fill this void. Within this paradigm, expert opinion is given the least weight, while practitioners’ clinical experiences are not even considered part of the evidence base.”
Active versus placebo
In a complimentary article in Nutrition Reviews, scientists led by Professor Jeffrey Blumberg from Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston explain that EBN departs from the EBM scenario, on the topic control groups.
“In EBM, the hypothesis is that adding an intervention ameliorates a disease, whereas in EBN it is that reducing the intake of a nutrient causes (or increases the risk of) disease,” wrote Prof Blumberg and his co-workers. “This distinction is critical.
“No one proposes in EBM that a disease is caused by the absence of its remedy; whereas for nutrients the hypothesis is precisely that malfunction is caused by deficiency. A hypothesis about disease causation can rarely, if ever, be directly tested in humans using the RCT design. This is because in the RCT the disease/dysfunction occurs in at least some of the study participants, and the investigators must ensure that this will happen,” they add.
“Instead where EBN must operate is with respect to two related, but different questions: (i) In addition to disease X, does the inadequate intake of nutrient A also contribute to other diseases? and (ii) At what level of intake of nutrient A is risk of all related disease minimized or all related functions optimized?”
So what?
Prof Blumberg and his co-authors indicate that the totality of the evidence must be used, because of the inherent limitations in testing nutrients in a RCT setting.
“This may mean action at a level of certainty that is different from what would be needed in the evaluation of drug efficacy,” they note.
“Because deliberately reducing intake to deficient levels in humans is ethically impermissible, the RCT will often not be available as a means of elucidating many potential nutrient-disease relationships. The general principles of EBN can provide a sufficient foundation for establishing nutrient requirements and dietary guidelines in the absence of RCTs for every nutrient and food group,” added Prof Blumberg and his co-authors.
Drs Shao and MacKay add: “EBN must consider the complex nuances of nutrients and bioactive food components to better inform the design and interpretation of nutrition research. Practitioners, researchers, and policy makers will be better served by a nutrition-centered framework suited to assess the totality of the available evidence and inform treatment and policy decisions.”
Source: Natural Medicine Journal
Volume 2, Issue 12, December 2010, Pages 10-18
“A Commentary on the Nutrient-Chronic Disease Relationship and the New Paradigm of Evidence-Based Nutrition”
Authors: A. Shao, D. Mackay
To read the full commentary, please click here.
Nutrition Reviews
Volume 68, Issue 8, Pages 478-484, doi:10.1111/j.1753-4887.2010.00307.x
“Evidence-based criteria in the nutritional context”
Authors: J. Blumberg, R.P. Heaney, M. Huncharek, T. Scholl, M. Stampfer, R. Vieth, C.M. Weaver, S.H. Zeisel