OBESITY IN NORTH AMERICA: An Overview

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Obesity is defined as a condition characterized by excessive bodily fat.95 The terms obesity and overweight mean different things to different people. Defining obesity and overweight has been the focus of scientific study for hundreds of years.23 The study of obesity has grown to include such issues as prevalence, morbidity, mortality, and psychosocial effects. This article discusses these topics and how they relate to the study of obesity today. First, definitions and various classifications of obesity are discussed.

Section snippets

DEFINITION AND CLASSIFICATION OF OBESITY

Although the conceptual definition of obesity is simply excessive body fat, its operational (clinical) definition has been controversial. The clinical definition of obesity is usually expressed in terms of body mass index (BMI), also called Quetelet's index, which is derived by dividing one's weight by the square of one's height: BMI = kg/m2 = 703(lbs/in2). Historically, various world bodies have used different BMI cutoff points to define obesity and overweight. In 1997, the World Health

PREVALENCE

Prevalence is defined as the total number of people in a population that are known to be overweight or obese at a given point in time, usually expressed as a percent of the total population. In the twentieth century, obesity rates in the United States, Canada, and Mexico grew substantially. The increased prevalence of obesity is examined in terms of sex, age, race, and place of residence.

MORBIDITY

There is some debate about whether there are health benefits to being thinner among individuals whose BMI is less than 25. A BMI greater than 25, however, clearly confers increased risk for a number of health conditions. Overweight and obesity have been associated with increased risk of a large number of disorders including but not limited to the following:

  • Dyslipidemias37, 38

  • Type II diabetes mellitus (non–insulin dependent diabetes mellitus [NIDDM])27, 31

  • Hypertension17, 64

  • Coronary heart

Evidence From Model Organisms

Some of the clearest effects of obesity on life span come from studies of laboratory rodents. When obese animals are compared with lean counterparts, there is a clearly shorter life span regardless of whether the obesity is due to single gene mutations,58, 61, 62, 79, 122 polygenic factors,122 or dietary induction.74 Consistent with these findings, life-prolonging effects are achieved by caloric restriction. Caloric restriction should not be taken to be synonymous with lower body weight or

PSYCHOSOCIAL ASPECTS OF OBESITY

So far the various roles excess weight plays in the physical health of obese persons have been discussed; it impacts not only morbidity, but also mortality. Obesity also plays a major role in the psychosocial realm. This section discusses the impact of obesity on a person's social and psychological functioning. Also examined is how obesity affects the social realm, including the areas of employment and educational opportunities, marital status, and treatment by health care professionals.

CONCLUSION

Obesity is a far-reaching problem in North America today. It is more prevalent than ever, and millions of people are at increased risk for a number of diseases as a result of obesity. In addition, there is a strong link between mortality rate and obesity. Obese people are also at risk for social discrimination and, possibly, adverse psychologic consequences. Much more work needs to be done in all areas of obesity to provide the best palliation, treatment, care, and, it is hoped, prevention of

ACKNOWLEDGMENT

The authors are grateful to Dr. Myles Faith and Dr. Moonseong Heo for their helpful comments.

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    Address reprint requests to David B. Allison, PhD, Obesity Research Center, 1090 Amsterdam Avenue, 14th Floor, New York, NY 10025, e-mail: [email protected]

    This article was supported, in part, by National Institutes of Health grants ROIDK51716 and P30DK26687.

    *

    Obesity Research Center, St Luke's–Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons, New York, New York

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