Diet, gym, supplements, or maybe it is all in your mind? A systematic review and meta-analysis of studies on placebo and nocebo effects in weight loss in adults.

INTRODUCTION: There is evidence that placebo and nocebo effects are significant for many conditions, but their impact on weight loss has not yet been well described. MATERIAL AND METHODS: A systematic review of studies indexed on PubMed, Cochrane, PsycINFO, PsycARTICLES, TripDatabase, and Embase was carried out. Studies (1) with at least two study groups - placebo and a corresponding control group; (2) published in English; and (3) focusing on adults participating in weight loss programs or on placebo/nocebo effects in weight loss were included. Synthesis and meta-analysis of the results of studies with comparable research plans were performed. RESULTS: Some preliminary trends suggesting placebo and nocebo effects in weight loss were found. Placebo effects manifested in trends towards a slightly greater reduction of Body Mass Index (BMI) and body fat ratio in the placebo compared with the control groups. On the other hand, in one study, it was found that the expectancy effects of taking oral weight-loss agents might be disadvantageous (i.e., because they elicit a nocebo effect on weight loss). CONCLUSION: The findings suggest a possibility that the nocebo effect may occur when an intervention has a medical context. In contrast, the placebo effect can be observed in cases where the intervention is of a different nature. However, considering the low number of studies analyzing the use of placebos in weight loss, new primary research is needed.

Order does matter: the combined effects of classical conditioning and verbal suggestions on placebo hypoalgesia and nocebo hyperalgesia.

ABSTRACT: In most experimental studies in which verbal suggestion and classical conditioning are implemented together to induce placebo effects, the former precedes the latter. In naturally occurring situations, however, the information concerning pain does not always precede but often follows the pain experience. Moreover, this information is not always congruent with experience. This study investigates whether the chronology of verbal suggestion and conditioning, as well as their congruence, affects placebo hypoalgesia and nocebo hyperalgesia. The effects induced in 15 groups were compared. The participants in 8 experimental groups were presented with verbal suggestions that were either congruent or incongruent with classical conditioning. The verbal suggestions were provided either before or after conditioning. In 2 other experimental groups, placebo conditioning or nocebo conditioning was implemented without any verbal suggestion; in 2 groups, verbal suggestion of hypoalgesia or hyperalgesia without conditioning was applied. The control groups without any suggestions or conditioning were also included. Placebo hypoalgesia induced by congruent procedures was significantly stronger when the suggestion of hypoalgesia preceded rather than followed conditioning. The order of the congruent procedures did not affect the magnitude of nocebo hyperalgesia. In the groups in which incongruent procedures were implemented, placebo hypoalgesia or nocebo hyperalgesia was in line with the direction of the last-used procedure, regardless of whether it was conditioning or verbal suggestion. The results show that not the type of the procedure (verbal suggestion or conditioning), but the direction of the last-used procedure shapes pain-related expectancies and determines placebo effects.

To Experience or to Be Informed? Classical Conditioning Induces Nocebo Hyperalgesia even when Placebo Analgesia Is Verbally Suggested-Results of a Preliminary Study.

OBJECTIVE: To investigate whether direct experience (i.e., classical conditioning) or verbal suggestion is more important in inducing nocebo hyperalgesia, five groups (total sample size, N = 99) were studied: conditioning, congruent conditioning, incongruent conditioning, verbal suggestion, and control. METHODS: Participants in groups with conditioning experienced more intensive pain stimuli after presentation of a white circle. In the congruent conditioning group, suggestion that the circle would precede more intensive pain stimuli was additionally provided, whereas in the incongruent conditioning group, the opposite suggestion was used. Control and verbal suggestion groups received pain stimuli of one intensity; however, the latter received suggestion that a circle would precede pain stimuli of higher intensity. RESULTS: The nocebo effect was observed in all conditioning groups, regardless of the verbal suggestions used. Moreover, the experience of hyperalgesia was able to nullify the effect of the verbal suggestion of analgesia. Incongruence between verbal suggestion and pain experience produced expectancies that affected nocebo hyperalgesia. CONCLUSIONS: The results of this preliminary study suggest that direct experience seems to be more important than verbal suggestion in inducing nocebo hyperalgesia.

Use of placebo interventions in primary care in Poland.

OBJECTIVE: The aim of the study was to investigate the behavior, beliefs and attitudes of Polish primary care physicians concerning the use of placebo interventions. SUBJECTS AND METHODS: A total of 220 Polish primary care physicians (internists, specialists in family medicine and pediatricians) were asked to participate in a questionnaire survey and 171 agreed to do so. The questionnaire was a self-report of the behavior, beliefs and attitudes of physicians concerning the use of placebo interventions in clinical practice. The percentages are based on the actual number of respondents to each question. RESULTS: Of 169 respondents, 135 (80%) declared that they used or prescribed placebo interventions, with 20/169 (12%) doing so almost every day, 51/169 (30%) once a week and 44/169 (26%) once a month. The most common placebos used were vitamins (86/135, 66%) and homeopathy (73/135, 56%). Among the participants, 114/129 (84%) reported that the placebos were effective, with only 10/129 (8%) considering them rarely effective; 75/139 (54%) of the physicians considered placebo interventions to be effective only in patients with subjective symptoms, 116/139 (73%) indicated that individual traits of patients were decisive factors in the effectiveness of placebo interventions, and 103/159 (65%) thought that the expectations of patients were of importance. A total of 128/170 (75%) respondents thought that the mechanism of placebo effects was purely psychological. CONCLUSION: The use and prescription of placebo interventions seemed to be very common among Polish primary care physicians studied and they generally had positive attitudes towards their use and effectiveness.