Weight cycling and its effects on muscle mass, sarcopenia and sarcopenic obesity.

The prevalence of obesity is rising around the world, as the number of subjects dieting and experiencing weight loss followed by unintentional weight regain, the so-called weight cycling (WC). In this narrative review we sought to reveal the effects of WC on body composition as well as to evaluate if WC may represent a risk factor for sarcopenia and sarcopenic obesity. The relative changes in lean and fat compartments after WC have been shown to depend on several factors as the degree of energy deficit, the rate of weight loss and baseline body weight, as well as sex, age, physical activity and subject's metabolic or hormonal status. Effects of WC on body compartments may be underestimated depending on body composition measurements, interference of physical exercise, number of WC, age and population characteristics. Studies using the most precise methods to assess body composition changes, as well those with higher number of WC and/or including old subjects, show that with WC, lower fat free mass (FFM) is regained with a mismatch between muscle and fat. In addition, when WC is involuntary in old age, it drives and accelerates the age-related loss of FFM, in particular in frail populations. Finally, an association between WC and sarcopenia or sarcopenia obesity, was also observed when evaluating strength together with WC-related body composition changes. In conclusion WC may act as an accelerator of biological aging, and it could be further investigated as a potential risk factor for sarcopenia or sarcopenic obesity.