A clinical trial with at least one active treatment group (e.g., taking a vitamin) and a control (e.g., placebo) group. In RCTs, participants are chosen for the experimental and control groups (e.g., placebo-controlled) at random, and are not told whether they are receiving the active or placebo treatment until the end of the study. A RCT in which neither the investigators administering the treatment nor the participants know which participants are receiving the experimental treatment and which are receiving the placebo is called “double blind”. RCTs are always prospective studies.
RCTs, the gold standard for drug testing, are considered to be of high quality because the risk of bias is minimized. An RCT can provide evidence and can establish cause-and-effect relationships (hypothesis-testing).
RCT cannot readily be applied to nutrients as it is not possible to compare the effect of micronutrient-intake with a control group without any dietary exposure. So far, no good metrics or measures (i.e., for micronutrient efficacy) to establish a baseline for comparisons (i.e. effect with vs. without micronutrient) are available.