Perspective: Fundamental Limitations of the Randomized Controlled Trial Method in Nutritional Research: The Example of Probiotics

Abstract

Studies on the relation between health and nutrition are often inconclusive. There are concerns about the validity of many research findings, and methods that can deliver high-quality evidence-such as the randomized controlled trial (RCT) method-have been embraced by nutritional researchers. Unfortunately, many nutritional RCTs also yield ambiguous results. It has been argued that RCTs are ill-suited for certain settings, including nutritional research. In this perspective, we investigate whether there are fundamental limitations of the RCT method in nutritional research. To this end, and to limit the scope, we use probiotic studies as an example. We use an epistemological approach and evaluate the presuppositions that underlie the RCT method. Three general presuppositions are identified and discussed. We evaluate whether these presuppositions can be considered true in probiotic RCTs, which appears not always to be the case. This perspective concludes by exploring several alternative study methods that may be considered for future probiotic or nutritional intervention trials.

FIGURE 1

Levels of evidence as discussed in references , , and . RCT, randomized controlled trial.

FIGURE 2

Relation between presuppositions, quality criteria, logic (and analyses), and evidence. Quality criteria are guidelines that aim to increase the quality of the evidence and logic in order to improve the validity of the conclusions. Presuppositions form the necessary frame within which research questions, approach, and assessment become meaningful and govern quality criteria, evidence, and logic. For the conclusions to be valid the presuppositions need to be true.