Because obesity rates have been escalating at annually measurable rates, much research money has been devoted to determining the underlying causes. Despite the world’s brightest and best scientific efforts, no single gene or direct pathway explaining obesity has been identified. Numerous genetic factors may contribute to an obesogenic genetic risk profile, but this profile is only an indicator of the potential for someone to gain excess weight under obesogenic conditions. It also happens that most humans share this genetic profile favoring weight gain. There has been no significant genetic shift, mutation, or other biological change in humans in thousands of years. Thus, if the obesogenic genetic risk profile has remained the same in humans since the obesity epidemic began, what has changed?
The answer to this conundrum is both simple and complex. The simple answer is that our environment has changed; the complexity lies in determining the aspects of our environment that have changed to make it obesogenic and how we can reverse the obesogenic environment.
The spectrum of causes of death when we compare today to a century ago is remarkably different in industrialized countries. A century ago, most people died from infectious diseases such as pneumonia or tuberculosis (table 1.1), and most people died young and often relatively quickly. Even if one was overweight or obese, it was less of a concern because the typical health-compromising conditions associated with obesity tend to happen later in life, a period in the life cycle that most people did not live long enough to see. In the past century, tremendous scientific advances in microbiology, improved understanding of contagions, and the technological innovation of vaccination have eliminated nearly all deadly infectious diseases from a century ago. Now people live longer lives free from many infectious diseases, and they tend to die much later in the life span from chronic health-compromising conditions that slowly reduce the capacity of one or more organ systems. The top causes of death in industrialized countries are all chronic diseases such as heart disease, cancers, and stroke, for which obesity, lack of physical activity, and dietary habits are strong contributors (Centers for Disease Control and Prevention [CDC] & National Center for Injury Prevention and Control [NCIPC], 2008).
The dramatic shift in causes of death in industrialized society reflects the changes in our environments and resulting lifestyles. Everything has changed. Technological innovation has changed the way our food is grown, prepared, and presented in the retail marketplace. Policies promoting economic growth while yielding to political pressures have changed the food supply. Economic growth and the globalization of the marketplace have increased communication and travel, influencing lifestyle habits and changing available jobs. School policies have changed the types of physical activities taught, if they are taught at all, and the kinds of foods youths learn to love at an early age. Our individual lives have changed. We buy our food already partially or wholly prepared rather than hunt or gather it ourselves. We travel to our jobs and schools by car rather than by foot. Many of us may rely on televisions and computers that bring the world directly to the comfort of our own homes. There are many more examples.