Modeling the dynamics of human energy regulation and its implications for obesity treatment
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Authors
Abdel-Hamid, Tarek K.
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Date of Issue
2002
Date
Winter 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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Article
Description
The article of record as published may be located at http://dx.doi.org/10.1002/sdr.240
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Citation
System Dynamics Review, Vol. 18, No. 4, (Winter 2002): pp. 431–471
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.