University of Missouri-Columbia School of Health Professions Link to MU Homepage link to MU Homepage School of Health Professions
search  
Virtual Health Care Team
Case StudiesAbout VHCTContinuing EducationHealth ReferencesContact UsHome

Lifestyle Management of Adult Obesity

Etiology of Obesity


Since the 1970's, Americans have become more health conscious. Blood pressure and cholesterol levels are lower and CVD mortality has decreased by more than half. Many experts suggest that at least half of the decline in heart attacks is due to improved lifestyles among Americans. In addition, low fat foods are abundant, health club memberships are up considerably, and athletic gear manufacturing is a multibillion-dollar industry.

However, overweight and obesity rates have continued to increase during this expansion of health-related industries. What are the causes for this apparent paradox of an increasingly overweight populace in the face of increasing attention to health issues? Katherine Flegal, PhD, an epidemiologist for the National Center for Health Statistics, (NCHS) states that “the data are confusing, but the causes of the obesity epidemic most likely are too much food and too little physical activity.” [38]

Although there have been landmark discoveries in the past decade of genetic contributions to obesity such as the Ob gene in mice, leptin, uncoupling proteins, and neuropeptides, these findings cannot explain the obesity epidemic. Human genes certainly have not changed dramatically in just 8 years from 1991-1998, a period over which there was a 50% rise in the prevalence of obesity. Studies suggest that 25% to 70% of obesity can be explained by genetics. [39] [40] Studies of twins suggest inheritance explains 25% to 40% of inter-individual differences in obesity. [41] A few single gene defects have been discovered such as congenital leptin deficiency or congenital leptin receptor deficiency.

However, in most cases, genes involved in weight gain do not directly cause obesity but rather they increase the susceptibility to fat gain in subjects exposed to an environment characterized by an abundance of food and limited physical activity. Some argue that “the culprit is an environment which promotes behaviors that cause obesity.” [42] [43] Some individuals with a genetic tendency may avoid obesity by maintaining habits of healthy eating and physical activity behaviors. [42] [43]

Thus, obesity is a complex, multifactorial chronic disease. Simply stated, body weight depends upon the balance between calories consumed and calories expended. This balance depends largely on genetic make-up, level of physical activity, and resting energy expenditure. If more calories are consumed than expended, the excess calories are stored as fat in the form of adipocytes. The more compelling issue, however, is why do some people store more calories than they expend? Is it because overweight people simply eat too much and engage in too little physical activity? Or are some persons predestined by their inheritance to be overweight or obese irrespective of their environment and personal habits?

Scientists have identified several dozen genes that appear to be connected to human obesity. In 1994, the OB gene was discovered. [44] The OB gene is responsible for the production of leptin in adipocytes, a hormone which appears to decrease appetite and stimulates metabolism. In humans, it was found that most obese persons have high levels of leptin due to their high levels of body fat. [45] As a result, low levels of leptin due to an absence of the OB gene does not appear to be a common cause of obesity. Thus, many scientists believe that some obese humans are “leptin-resistant” in much the same way persons with type 2 DM are “insulin-resistant.”

American society has evolved into an environment which facilitates weight gain. Studies show that only approximately 20% of Americans achieve the minimum public health goal of 30 minutes of moderate intensity physical activity on most days of the week. [46] This percentage has essentially been the same for nearly three decades. However, the population has increased by ~60 million during that same period. Thus, the absolute number of Americans achieving 30 minutes or more of physical activity has increased from 44 million in 1975 to 56 million in 2000, resulting in 48 million more sedentary or irregularly active persons.

Food is readily available and in “super-sized” portions. In fact, a study of the ecological basis of the increased US prevalence of obesity estimated that food availability has increased 15% since the mid-1970's. [2] Physical activity has been all but “engineered” out of our vocational and leisure-time pursuits. This environment facilitates obesity by promoting overeating and discouraging physical activity. As an example of the cultural pressure towards a positive energy balance, Yanovski et al. reported that the average American gains 1-2 lbs during the yearly holiday season. [47] Over ten years, this amounts to a 10-20 lb weight gain.

The US also is a leading innovator of passive entertainment. Television viewing is positively related to obesity and the development of diabetes. [48] [49] The average adult American spends half his or her leisure time watching television. Combine this with jobs that involve little physical activity, plus video games, computing, gambling, etc., and it becomes apparent why daily caloric expenditure has declined precipitously since the 1950's and 60's.

Other factors that contribute to the obesity epidemic include the high energy density and fat content of processed foods, increased prevalence of eating out, particularly at fast food restaurants, availability of food in gasoline stations, vending machines, and in discount and department stores. Essentially, the US culture seems to have created an environment of “sedentarism and obsessive-compulsive eating.”

It is beyond the scope of this case to review in detail the causes of obesity. However, this case shows that obesity can be successfully treated through lifestyle changes, and describes the environmental factors that increase susceptibility to obesity.


Published by the Virtual Health Care Team ®
School of Health Professions
University of Missouri-Columbia
Questions? Comments? Contact Us
Copyright © 2011-2012 — Curators of the University of Missouri
DMCA and other copyright information.
An equal opportunity/ADA institution.
All rights reserved. Disclaimer and Terms of Use
Last Update: March 6 2013