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        Modeling the dynamics of human energy regulation and its implications for obesity treatment

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        Author
        Abdel-Hamid, Tarek K.
        Date
        2002
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        Abstract
        Obesity has reached epidemic proportions in the United States and is threatening to become a global epidemic. Even more concerning, the incidence of overweight continues to increase. The health consequences and economic costs to individuals and to society are considerable. Obesity is associated with many serious health complications, including coronary heart disease, type 2 diabetes mellitus, hypertension, selected cancers, andmusculoskeletal disorders. In the U.S., direct and indirect medical costs attributable to obesity are estimated to approach $100 billion yearly. Obesity develops when a chronic imbalance exists between energy intake, in the form of food and drink, and energy expenditure. To date, the emphasis of treatment has been on the energy intake side of the energy balance equation. This, in part, is because it has been difficult to demonstrate the efficacy of exercise as a treatment strategy. This paper attempts to demonstrate the utility of system dynamics modeling to study and gain insight into the physiology related to weight gain and loss. A simulation model is presented that integrates nutrition, metabolism, hormonal regulation, body composition, and physical activity. These processes are typically fragmented between many different disciplines and conceptual frameworks. This work seeks to bring these ideas together highlighting the interdependence of the various aspects of the complex human weight regulation system. The model was used as an experimentation vehicle to investigate the impacts of physical activity on body weight and composition. The results replicate the ‘‘mix’’ of results reported in the literature, as well as providing causal explanation for their variability. In one experiment, weight loss from a moderate level of daily exercise was comparable to the loss from dieting (when both produced equivalent energy deficits). Perhaps of greater significance, the exercise intervention protected against the loss of fat-free mass, which occurs when weight loss is achieved through dieting alone, and thus promoted favorable changes in body composition. In a second experiment, exercise regimens of moderate to high level of intensity proved counter-productive as weight-reducing strategies for an obese sedentary subject. This was due to the limited energy reserves (specifically, muscle glycogen) available to such individuals. However, when the diet was changed from a balanced composition to one that was highly loaded with carbohydrates, it became possible to sustain the intense exercise regimen over the experimental period, and achieve a significant drop in body weight. The results underscore the significant interaction effects between diet composition and physical activity, and emphasize the critical role that diet composition can have in exercise-based treatment interventions.
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        The article of record as published may be located at http://dx.doi.org/10.1002/sdr.240
        URI
        http://hdl.handle.net/10945/43631
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          Exercise and Diet in Obesity Treatment: An Integrative System Dynamics Perspective 

          Abdel-Hamid, Tarek K. (2003);
          Purpose: Demonstrate the utility of System Dynamics computer modeling to study and gain insight into the impacts of physical activity and diet on weight gain and loss. Methods: A holistic System Dynamics computer model ...
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          Eureka: Insights into human energy and weight regulation from simple - bathtub-like - models 

          Abdel-Hamid, Tarek K. (2012);
          Recent research findings reveal that human bioenergetics belongs to the class of multi-loop nonlinear feedback systems - the same class of systems that system dynamics aims to study. In this paper the author aims to demonstrate ...
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          The influence of temperature and composition on the activation energy for creep in binary aluminum lithium alloys 

          Seaton, Robert Leonard (Monterey, California: Naval Postgraduate School, 1990-12);
          With the fast pace of technology in the aerospace industry, there are increasing demands for higher strength and stiffness in structural materials but with reduced weight and improved formability. Aluminum alloys have been ...
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