ENERGY BALANCE AND OBESITY

Chapter Introduction

The Sitting Disease UNDERSTANDING THE CAUSES AND CONSEQUENCES OF OBESITY

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LEARNING OBJECTIVES

List the health consequences associated with obesity and describe how excess body fat increases the risk of developing these conditions (Infographics 15.1 and 15.3)
Describe the concept of energy balance (Infographics 15.2 and 15.4)
Identify and describe the components of total energy expenditure (Infographic 15.5)
Describe factors that affect basal metabolic rate (Infographic 15.6)
Describe activities that are examples of nonexercise activity thermogenesis (NEAT) (Infographic 15.7)
Describe factors that contribute to the development of obesity (Infographic 15.8)
Use body mass index and waist circumference to evaluate someone’s risk of chronic disease (Infographics 15.9, 15.10, 15.11)
Describe methods for determining body composition (Infographic 15.12)
Discuss strategies for successful weight loss and maintenance (Infographics 15.13 and 15.15)

When James Levine was 11 years old, he began a science experiment in his bedroom. His test subjects? Snails.

In glass-walled fish tanks he built himself, Levine collected pond snails from nearby Regents Park in his native London. He then methodically monitored and recorded their movements. “My idea was that every snail has a built-in hard-wired style of movement,” explains Levine. “One snail will do swirly-whirly-whirly, while another snail will always move in a straight line.”

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Dr. James Levine and his treadmill station. Levine, a professor of medicine at the Mayo Clinic and Arizona State University, is an expert on the physiology of weight gain and loss.

AP Photo/Jim Mone

To test this hypothesis, every night, between the hours of 9 PM and 5 AM, he’d wake up hourly with an alarm clock and mark on the glass where the snail had moved. At the end of the night, he’d trace each snail’s journey.

“Not surprisingly, I was constantly asleep at school,” Levine confesses.

By the time he finished his experiment, Levine had 270 snail tracings. What he discovered was that snails didn’t quite sort the way he thought. But they did have stereotypical styles of movement. “Joanna [he gave each snail a name] always does ziggidy-zaggidy-ziggidy-zaggidy. And John always moves in a smooth way.”

The snail experiment had a lasting impact on Levine, who eventually went on to medical and graduate schools. Now, 35 years later, Levine has focused his love of experimentation on another slow-moving creature: the human couch potato.

OBESITY excess amount of body fat that adversely affects health

Levine, a professor of medicine at the Mayo Clinic and Arizona State University, is an expert on the physiology of weight gain and loss, with a special focus on obesity. Obesity—having excess body fat—has been called American’s number one health crisis. Obesity has been linked to a whole host of health problems, including heart disease, diabetes, stroke, Alzheimer disease, hypertension, and even certain cancers. It is also a major killer: In the United States, only tobacco use causes more premature deaths per year. (INFOGRAPHIC 15.1)

INFOGRAPHIC 15.1 Prevalence and Health Consequences of Obesity in the United States

Question 15.1

Looking at the graph, how would you describe the change in the number of overweight (nonobese) adults?

To understand how the percentage of overweight (not obese) adults has grown, subtract the red line (obese adults) from the orange line (obese adults and overweight adults combined). The number of overweight adults has increased approximately 5% from 1960 to 2012 (from approximately 30% to 35%). The number of obese adults has increased 23% in that same time (from approximately 12% to 35%).

OVERWEIGHT a moderate amount of excess body fat or an excess amount of body weight from muscles, bone, fat, and water

Alarmingly, rates of obesity have sky-rocketed over the past four decades, leading many to refer to an obesity “epidemic.” As of 2014, more than one-third of U.S. adults were obese, and more than two-thirds were overweight or obese, and the prevalence of obesity in children is increasing at a similar rate. The United States is not alone: Global obesity rates have almost doubled since 1980 and the World Health Organization estimates that more than 10% of the world adult population is obese.

Obesity is a complex disease that is influenced by multiple factors; genetics, environment, and behavior are the main causes. Genetics is seen as the primary factor determining an individual’s susceptibility to obesity. However, the rapid rise in the prevalence of obesity in the last few decades is largely attributed to changing environmental factors, because human genes have essentially remained the same over this time. For this reason it is said that, “Genetics loads the gun, and environment pulls the trigger,” because the environments that we live and work in can strongly affect our behaviors. For example, the built environment—our surroundings that are designed by humans—can strongly affect how likely we are to engage in physical activity. Also, the social and physical factors that influence the foods we eat (the food environment) can make it challenging for us to make healthy food choices. Consequently, the dramatic rise in obesity is believed to result from environmental changes that promote low levels of physical activity and the consumption of energy-dense foods that are particularly likely to promote weight gain in genetically susceptible individuals.

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Although almost everyone agrees that obesity seriously compromises our health and longevity, scientists are divided about just what is causing our waistlines to expand at an ever-alarming pace. Is it increased food intake—linked perhaps to larger portion sizes in restaurants and in supermarkets? Or is it decreased energy expenditure—a result of our increasingly sedentary lifestyle? Arguments have been made on both sides of the coin, but no strong consensus has emerged. Now, with the help of some clever experiments using sophisticated undergarments, Levine thinks he has found the answer.