Fasting has been advocated as an effective way to reduce body weight. However, few data support any long-term effect of this therapy. On the contrary, evidence is accumulating that the repeated weight loss and concomitant weight gain, typical of fasting in many individuals, will lead to a subsequently higher body weight. Each weight cycle seems to increase the risk of a higher waist/hip ratio, greater metabolic efficiency and a food preference towards fat. All these trends result in further problems associated with weight loss and a vicious circle is established.