A Guide to Constructing and Conducting Randomized Clinical Trials on Weight Management Therapies


This case is about a single-blind randomized clinical study of the potential existence of placebo effects in dieting. It is well known that presently obesity is prevalent in developed countries. Weigh management, however, is a complex process, which has many facets apart from the simple “calories in, calories out” paradigm. This born the idea of experimenting with a combined weight-loss program for investigating whether body composition parameters may be influenced by a potential placebo effect of dieting. We recruited 14 healthy adults of both sexes aged between 19 and 45 years with body mass index (BMI) >27 to participate in the study. They were randomly assigned to two groups—one experimental and one control. The subjects in the experimental group followed an isocaloric diet but were told they were on a calorie-deficient regimen. The subjects in the control group were aware that their regimens were energy balanced. All participants were engaged in regular sessions of resistance exercise 3 times a week. We studied within-group differences in body mass, percentage of fat tissue, and BMI. All three variables reduced in value in the experimental group. Of course, the study construct suffered some methodological biases, due mainly to the small sample sizes and the lack of 24/7 adherence control. Nevertheless, in our opinion, the changes in the parameters we measured in the experimental group may be (at least partially) influenced by a placebo effect. We were quite aware since the very beginning that even if our results proved that a placebo effect existed, most probably, they would not be robust enough to cover the standard requirements of statistical power. For that reason, we intended to only base a hypothesis on them, which to be tested in further replication studies.

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