The "dynamic epidemiology" of obesity: knowledge to help improve our ability to manage the condition

AMAA Journal, Summer, 2004 by Steven Jonas

Editor's Note: For this issue, I am combining my usual Editorial and "Talking About Training" column into this one article. While it does not directly address a matter of training, it does address a subject that is closely related to training and why many people do it: control of overweight. And while its rationale is based in the literature, it is also a piece of advocacy. And so this one piece serves two purposes. As a disclaimer, I should note that I do neither laboratory nor field research in this subject area. While I would very much like to see it done, I have no personal interest of any kind in pursuing any of the lines of research I discuss in this paper.

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Introduction

As is well known, the epidemic of overweight/obesity (O/O) in the United States has gathered momentum over the last 20 years. Long-term, the answer is of course prevention. But in the meantime there is a massive problem about how to deal with the epidemic presently and for the foreseeable future. The science of epidemiology, that is the study of the distribution of disease and negative and positive states of health in populations, can be very helpful in this regard.

At present, a good deal is known about what can be termed the "static" epidemiology of obesity: what the overweight population looks like at a given point in time in terms of demographic and health-related characteristics. However, little is known about the patterns of weight gain and loss over time in individuals and populations, what might be termed the "dynamic" epidemiology of the condition. Who gains, how and why? Who is at risk? Who isn't? What are the several different weight-gain patterns?

On the other side of the ledger, what are the factors in weight loss success and failure? It is well-known that the success rate for losing weight and keeping it off is low; however, some people are successful in losing weight and keeping it off over time. Knowledge of the similarities and differences between those overweight persons who are successful in losing weight and those who are not, in both their individual and weight-gain and weight-loss characteristics, is also limited. This paper addresses these issues and in so doing offers a research agenda for elucidating them.

The Shape of the Problem

The epidemic of O/O in the United States has gathered momentum over the last 25 years, has been known to exist for quite some time and appears to be continuing unabated (19, 21, 2, 8, 13, 22, 14, 27, 29, 7, 23, 10, 11, 26, 4, 9, 20, 17, 18). O/O has very serious negative effects for our society. It is estimated that about 400,000 deaths annually are attributable to it and its stable mate, sedentary lifestyle (4). Also, it has been estimated that the health-related costs of O/O and its negative health outcomes are associated with approximately 10% of national health care expenditures (16).

There are numerous approaches to weight management and weight loss. Some of them work for at least some of those who try them: the person is able to lose weight and keep it off. Healthy eating combined with regular exercise has been established as the scientifically sound approach to weight loss and does appear to be the approach most commonly used by those who are successful in losing weight and keeping it off (5). But no single program works for everyone who tries it, and many don't work for anyone who tries them. Obviously, one size does not fit all when it comes to weight loss, or weight maintenance for that matter. There are many questions still unanswered. Finding answers could be of great assistance in developing a better approach to weight management and loss.

Definitions of Overweight and Obesity

Traditionally, "overweight" has been defined as excess body weight in relation to observed norms in the population by age, sex and height (28). Traditionally, the term "obesity" has been defined as an excess proportion of body fat in relation to observed norms in the population by age, sex and height, regardless of weight. That is, a person of normal weight carrying a higher than normal proportion of body fat would have been characterized as "obese."

In the current era, somewhat different definitions of the two terms are being used (19, 21). Rather than referring independently to excess body weight and excess body fat, presently the definitions of both conditions refer to an elevation in an individual's body mass index (BMI), which measurement comprehends both weight and height. Thus, the two terms now simply represent different degrees of excess. The term "overweight" refers to a BMI of 25 through 29 and "obesity" to a BMI of 30 or more. Since "obesity" is now used simply to refer to a higher degree of the generic condition "overweight," in this paper the combined term "overweight/obesity" (as noted above, abbreviated as "O/O") is used.

The Elements of the Dynamic Epidemiology of Obesity

Going beyond the well-understood "static epidemiology," consider the following. Over time, just who gets heavy and why? How does adult weight gain differ, over time, from childhood weight gain? Are weight gain and weight loss simply related to the calories-in/calories-out balance? Or is there a role played, in certain people at least, by the characteristics of individual metabolism and its possible variation from person to person? Are there variations over time in the way a given person gained weight that affects the probability of success or failure using a given weight loss program at a given point in time? In a person with O/O does previous dieting history have an impact, positive or negative, on current weight loss attempts? Does metabolism--that is, active metabolism, not just resting metabolic rate--vary significantly among people of normal weight and also among the overweight and obese? If so, are there also variations between the several groups, over time? Further, what are the epidemiological characteristics of the several groups? These are all versions and elements of the question: Why might it be important to gain an understanding of the "dynamic epidemiology" of O/O?