Obesity and exergy behavior of human body: A first approach

Abstract

Exergy behavior of human body for standard and healthy subjects has already been determined by few authors, including estimative of life expectancy from values of generated entropy and destroyed exergy for different societies. Besides, an increase of obese population is being observed in modern society, as well as an increase of mortality rate among this population. In the present work, exergy analysis is applied to human body in order to evaluate the effect of obesity on exergy behavior of the body and to estimate life expectancy by means of an index called exergy age. The analysis takes into account exergy rates and flow rates due to convection, radiation, respiration, evaporation and exergy metabolism. A cylindrical model of human body divided into four layers is utilized. Three groups are evaluated: control (20% of body fat), moderately obese (30%) and obese (36%). Exergy destroyed rate is determined for the three biotypes along life cycle. By integrating its values overtime, it is observed that obese subjects destroy more exergy during their lives than lean ones. However, regarding total exergy destroyed per mass unit, which is claimed to have a maximum value during lifespan, exergy destruction is greater in control group. Determination of exergy age index indicates that life expectancy of moderately obese would be 8.4 years greater than lean subject, while obese subject would live 16.1 years more. When exergy efficiency and performed work are evaluated, it becomes clear that, on exergy basis, an obese body is less efficient than a lean one, destroying more exergy to perform the same amount of work. Present results indicate that obesity jeopardizes exergy behavior of human body, turning it into a less efficient apparatus, what may lead to development of the so-called obesity-related diseases.

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