In an attempt to lose weight, too often people experience repeated cycles of weight loss followed by weight regain when the diet strategy is interrupted (often called weight-cycling or yo-yo dieting). The topic of weight-cycling and its health-related consequences, such as obesity, cancer, type 2 diabetes mellitus, and hypertension have been the source of considerable controversy. Several large population based prospective studies clearly illustrate an association between weight-cycling and an increased risk for all-cause and cardiovascular mortality, whereas others have not shown a change in risk. The link between weight-cycling and increased cardiovascular mortality are not well understood; however, enhanced weight regain, alterations in the composition and quantities of tissue lipids, impaired insulin signaling, and elevated plasma triglyceride levels have been observed in both human and animal models of weight-cycling.
The use of physical activity is a common strategy for the prevention of obesity and to improve the efficacy of weight reduction. Interestingly, when weight reduction interventions that incorporate physical activity have been interrupted, the amount of weight-regained has been inconsistent. This can be attributed to the various volumes and intensities of physical activity performed in these observational studies. The consequences of weight regain with and without physical activity on nonalcholic fatty liver disease (NAFLD) remains unknown.
The specific aims for the current project being conducted in the Exercise Biochemistry and Physiology Laboratory are to 1) define how weight-cycling (the cycle of weight-loss followed by subsequent weight regain) effects the development of NAFLD and 2) to determine if physical activity during weight-cycling provides protection beyond what is observed during “diet-only” induced weight-loss and also during subsequent weight regain.
It is hypothesized that 1) weight-cycling will cause a more advanced state of NAFLD and 2) physical activity will prove to be a powerful non-pharmacological strategy for the treatment of NAFLD, providing protection during subsequent weight regain. Nonalcholic fatty liver disease is characterized by 1) insulin resistance, 2) enhanced inflammatory state, and 3) excessive lipid storage (lipotoxicity). The therapeutic role of physical activity on these three key factors in the pathogenesis of NAFLD during weight-cycling will be evaluated in this investigation.