In this meta study, a study of studies, published in Journal of Consulting and Clinical Psychology 1996. Vol.64, No. 3, 517-519, it was found that weight loss programmes that included hypnosis resulted in significantly greater amounts of weight reduction.
“In a 3rd meta-analysis of the effect of adding hypnosis to cognitive-behavioral treatments for weight reduction, additional data were obtained from authors of 2 studies, and computational inaccuracies in both previous meta-analyses were corrected. Averaged across posttreatment and follow-up assessment periods, the mean weight loss was 6.00 Ibs. (2.72 kg) without hypnosis and 11.83 Ibs. (5.37 kg) with hypnosis. The mean effect size of this difference was 0.66 SD. At the last assessment period, the mean weight loss was 6.03 Ibs. (2.74 kg) without hypnosis and 14.88 Ibs. (6.75 kg) with hypnosis…”