Activity Anorexia

Theory, Research, and Treatment

W. Frank Epling, W. David Pierce

• Publisher: Psychology Press
• Year: 2013
• Print ISBN:
  9780805819298
• eBook ISBN:
  9781134794577
• Topic: Psychology
• Subtopic: History & Theory in Psychology
• Index: Psychology

This volume provides researchers and clinicians with an insight into recent developments in activity anorexia. Much of the basic information on the topic has come from animal literature; the theory of activity anorexia is built on an animal model of self-starvation (rats placed on a single daily feeding run more and more, over days stop eating, and die of starvation). Additionally, experiments that for ethical or practical reasons could not be done with humans may be conducted with other animals. The animal research is extending the understanding of biologically-based reward mechanisms that regulate eating and exercise, environment-behavior interactions that affect anorexia, and the biochemical changes that accompany physical activity and starvation.

Increasingly, however, the impact of physical activity on human anorexia is being directly investigated--eight out of fourteen research chapters in this volume are based on human research. Some researchers are interested in the impact of hyperactivity and caloric restriction on human reproductive function. Other authors are investigating physically active subgroups of people considered to be at risk for anorexia. Finally, several clinician/researchers suggest how physical activity and extreme dieting interact for anorexia nervosa patients.

Chapter authors were asked to present their views independent of the editors' argument that, when it is present, physical activity is central to anorexia. Many of the contributors disagree with the editors about the details of activity anorexia. A few suggest that excessive physical activity is either incidental to, or an epiphenomenon of, anorexia. Most authors are, however, in accord with the view that physical activity reduces food consumption which further drives up activity that results in even less caloric intake. No matter what their perspective, all contributors agree that hyperactivity frequently accompanies self-starvation in humans and other animals. The end result is a lively book that provides a source of ideas for both researchers and practitioners.

I

Principles and Processes of Activity Anorexia

1

An Overview of Activity Anorexia

W. Frank Epling

W. David Pierce

University of Alberta

Activity anorexia is a biologically based self-starvation syndrome that is triggered by diet and exercise routines. The syndrome occurs in several species of animals including rats and humans. For humans who live in affluent parts of the world, type of diet and exercise patterns are largely determined by sociocultural factors. For other animals, diet is a function of food availability, and exercise is mostly due to response feedback or stimulation from the environment.¹ Whatever factors produce it, severe food restriction in combination with excessive physical exercise can lead to what we call activity anorexia. Activity anorexia occurs when food intake declines, and this reduction in caloric intake results in an increase in physical activity. Increased physical activity causes an additional decline in food intake, which further increases activity, and so on. This simple negative feedback loop organizes several diverse research literatures with regard to human anorexia.

Many animals exposed to a significant reduction in caloric intake respond by increasing their physical activity. At first glance this does not seem to make sense. Why would an organism that is challenged by food reduction increase its caloric expenditure? Some animals do, in fact, reduce their energy output when food is scarce. For example, some species (e.g., ground squirrels) that are routinely exposed to food depletion survive by reducing their metabolic rate and by hibernating through periodic famines (see Mrosovsky & Sherry, 1980, for other examples). Consider, however, an organism that is dependent on a stable year-round food supply. If an environmental catastrophe threatens starvation, the animal that becomes mobile may travel to a new and plentiful food patch.

Chaotic dieting, excessive activity, and physiological abnormalities are associated with human anorexia. Willful self-starvation by humans is usually diagnosed as anorexia nervosa (AN), and patients are treated as mentally disordered. Our contention is that most cases of AN are in fact instances of activity anorexia (see Epling & Pierce, 1991, for detailed evidence). Activity anorexia is functionally defined and occurs when a decline in food consumption increases physical activity. Central to this description is that as physical activity becomes excessive, food intake is reduced, and the reduction in caloric intake leads to more activity, and so on. Eventually this feedback cycle may lead to starvation and death.

The chapters in this book represent a wide diversity of opinion and findings about the role of physical activity for anorexia. Topics range from reproductive function and eating disorders in humans to neurotransmitters and activity in semistarved rats. Several authors argue that the excessive activity observed in anorectic patients is mediated by cognitive factors; others focus on neuroendocrinology, biology, or behavioral processes. Some researchers are trying to discover the fundamental nature of the locomotor activity that food-restricted rats and patients with AN exhibit. Others suggest that the activity seen in activity anorexia is a side effect of more central processes and that the syndrome is thus incorrectly labeled. Despite these differences of opinion, all would agree that excessive physical activity is a prominent feature of self-starvation for anorectic animals and for AN patients.

Activity Anorexia

We have developed an animal model of the process of activity anorexia and a biobehavioral theory (chapter 3) that incorporates the animal results as well as convergent evidence at the human level. In this chapter we describe activity anorexia in rats and outline the convergent evidence from several literatures for a human variant of activity anorexia.

A Laboratory Model of Activity Anorexia

Under certain environmental conditions rats self-starve, and this phenomenon appears to be functionally similar to so-called willful starvation by humans (AN). In our laboratory, adolescent rats, approximately 60 days old, are placed in a cage that is attached to a running wheel. The wheel and side cage can be separated by closing a sliding door (Fig. 1.1). During the first 5 days of an experiment, the door that separates the side cage from the wheel is closed. Food is freely available in the cage and each animal can eat as much as it wants. The amount eaten is measured daily and the rats are also weighed each day (see Pierce & Epling, 1991, for a more complete description).

Fig. 1.1. A standard 1.1-m Wahmann running wheel with an attached side cage. A sliding door prevents or permits access between cage and wheel. Reprinted from W. F. Epling and W. D. Pierce (1991). Solving the Anorexia Puzzle: A Scientific Approach. Toronto: Hogrefe & Huber. Reprinted with the permission of Hogrefe & Huber Publishers, Seattle Toronto Bern Göttingen.

The food and weight measures provide baseline points for the experimental interventions, which combine food restriction and opportunity to run on a wheel. In a typical experiment, the animals are restricted to a single 60- or 90-minute daily meal. Following the meal, the doors to the wheels are opened and experimental animals are allowed to run. Control animals receive the same treatment, but the wheels will not turn.

Several procedural points are noteworthy. Experimental animals are given continuous access to the wheels except during the feeding period. In this way, running does not compete with eating. When wheels are available, there are no programmed contingencies for running. The animals can stay in their cages, sit in the running wheels, walk rather than run on the wheels, or respond in any other way.

The initial effect of placing animals on 1 meal a day is a large drop in food consumption (see Fig. 1.2). This is not surprising because the animals have not experienced a rapid change in food supply and are not adapted to the new feeding schedule. When food restriction and the opportunity for wheel-running occur together a number of interesting effects are observed. As shown in Fig. 1.2, experimental animals begin to run on the wheels. They increase running behavior over time even though there is no requirement to do so. This is an unusual response, because energy expenditure increases at a time when food intake is limited. Within a week, increases from several hundred to thousands of revolutions a day. Importantly, control animals, who cannot run, adapt to the feeding schedule within several days and remain healthy.

Fig. 1.2. Effects of food restriction (one 60-minute meal a day) and access to a running wheel for a typical rat. The figure shows food intake in grams (top), number of revolutions of a 1.1-meter wheel (middle), and body weight in grams (bottom). The thin solid line represents baseline from experimental phases.

A more startling effect is that food intake at the meal declines as running becomes more and more excessive. At the end of 1 week, the animal may not eat at all. The physical activity does not appear to be stressful (Spigelman, McLeod, & Rockman, 1991), and failure to eat is not due to the development of activity-stress ulcers (Doerries, Stanley, & Aravich, 1991). Recent findings by Belke and Heyman (1993; chapter 4, this volume) indicate that running generated by food restriction has reinforcing properties (opportunity to run will support lever-pressing by rats on variable-interval schedules). The animals in the activity anorexia experiment give up eating based on a reinforcement process that involves increasing energy expenditure through wheel-running. A typical rat may run up to 15 kilometers per day at the peak.

If the process of activity anorexia is allowed to continue, animals become weaker and weaker, food intake declines, activity subsides, and they die of starvation. The seemingly willful starvation and excessive exercising of these animals appears similar to many cases of AN.

Animal and Human Anorexia

Observations like these suggest clinical applications. This is because the laboratory phenomena appear to be functionally similar, to what has been labeled AN in humans (see chapters 15 and 16). We suggest that activity anorexia, not AN, is the issue. That is, many cases of activity anorexia have been incorrectly called AN. One way to establish functional similarity between an animal model and human pathology is to gather convergent evidence, which involves documenting diverse findings from various sources that together support or refute the relationships observed in the laboratory. The strongest form of convergent evidence occurs when a researcher is unable to predict the outcome of this search. In order to extend the activity anorexia model to the human level, we suggest six levels of functional similarity by convergent evidence (Pierce & Epling, 1991).

Excessive Physical Activity is Associated With Anorexia in Humans.Based on our early animal research (Epling, Pierce, & Stefan, 1981), we wondered if anorectic patients were in fact hyperactive. Epling, Pierce, and Stefan (1983) and Epling and Pierce (1988) reported on the mounting evidence for a relationship between physical activity and AN. We found numerous reports of hyperactivity in anorectic patients (Blitzer, Rollins, & Blackwell, 1961; Crisp, 1965; Halmi, 1974; Katz, 1986; King, 1963; Kron, Katz, Gorzynski, & Weiner, 1978; Slade, 1973). Kron et al. (1978) conducted a retrospective study of hospitalized anorectics and concluded that hyperactivity is a central feature of AN.

To illustrate, Katz (1986) reported that a physician became anorectic, going from 175 to 115 pounds, after starting a running program that increased to 50 miles per week. Hip pain made running difficult and the man compensated by extensive walking and cycling. Beumont, Beumont, and Touyz (chapter 15) point out that there is commonality of presentation between obligatory runners and anorectic patients and that overactivity is an important clinical feature for many anorectic patients. Davis, Kennedy, Ralevski, and Dionne (1994), using an in-depth interview technique, obtained a lifetime sport and exercise profile for anorectic patents. They concluded that sport and exercise can be central, causative, or both for anorexia (see also chapter 16).

Katz (chapter 17) noted that there are problems with most reports of excessive exercise in anorectic patients (e.g., most studies do not have a control group, but see Davis, Kennedy, Relevski, & Dionne, 1994, for an exception). Nonetheless, Katz said that the available data suggest that 65% to 75% of anorectic patients exercise excessively. In a respected series of papers, Yates and her coworkers (chapter 14, this volume; Yates, 1991, 1992; Yates, Leehey, & Shisslak, 1983; Yates, Shisslak, Allender, & Crago, 1992) noted that obligatory runners and anorectics engage in similar behavior. Further, Yates (chapter 14) suggests that the overtrained athlete (who is close to collapse but will not stop exercising), the exercising anorectic patient, and the anorectic rat running on an activity wheel seem similar to one another. They all appear to be locked into a compulsion to exercise.

Physical Activity Reduces Food Intake.Research on nutrition and behavior confirmed our speculation that humans reduce food intake when physical activity becomes excessive (Edholm, Fletcher, Widdowson, & McCance, 1955; Epstein, Masek, & Marshall, 1978; Johnson, Mastropaolo, & Wharton, 1972; Mayer, Roy, & Mitra, 1956; Watt, Wiley, & Fletcher, 1976). For example, Edholm et al. (1955) reported that military cadets ingest less food on drilling days than they do on days of lower activity. Epstein et al. (1978) found that obese school children would voluntarily reduce food intake following a prelunch exercise period.

Generally, increasing physical activity reduces food consumption. This effect occurs when physical activity is increasing against an individual’s base rate and subsides when activity stabilizes (Epling & Pierce, 1984, 1989). Once activity stabilizes, food intake recovers and may increase in order to compensate for the additional caloric expenditure (Tokuyama, Saito, & Okuda, 1982). Of course, when starvation becomes extreme, activity decreases. This lethargy is also observed in our laboratory rats near the end of the activity anorexia cycle.

Lower Food Consumption Increases Physical Activity.There is other evidence that lower food consumption increases physical activity in humans (Blanton, 1919; Howard, 1839; Russell-Davis, 1951) and in rats (Boer, Epling, Pierce, & Russell, 1990; Russell, Epling, Pierce, Amy, & Boer, 1987). A controlled experiment on human starvation was conducted by Keys, Brozek, Henschel, Mickelson, and Taylor (1950). In this study, 36 conscientious objectors to World War II were required to undergo 6 months of semistarvation. Although Keys et al. emphasized the inactivity of the men, their procedures may have masked the expected increase in physical activity when food is restricted. The men were required to participate in a regular physical activity program, hike 22 miles a week, and walk 2 to 3 miles a day back and forth to the mess hall. Each man was also required to do a weekly 30-minute test on a motor-driven treadmill at 3.5 miles per hour on a 10% gradient.

In spite of this, there is evidence that food deprivation induced excessive physical activity. The researchers stated, “Some men exercised deliberately at times. Some of them attempted to lose weight by driving themselves through periods of excessive expenditure of energy” (p. 828). Keys et al. interpreted this exercising as a deliberate attempt by the men to lose weight in order to have their food ration increased. A more likely explanation is that these men were experiencing the activity anorexia cycle. Overall, the study by Keys et al. and other evidence indicate that humans increase physical activity when food intake declines and become inactive when starvation is severe (see Epling & Pierce, 1988, 1991; Epling, Pierce, & Stefan, 1983, for reviews).

The Onset of Anorexia in Humans and Animals Develops in a Similar Manner.Another line of convergent evidence shows that the onset of anorexia in humans is consistent with the pattern observed in animals. In the laboratory, food restriction generates exc...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright
• Contents
• Contributors
• Preface
• Part I: Principles and Processes of Activity Anorexia
• Part II: Behavioral Foundations of Activity Anorexia
• Part III: Physiological Foundations of Activity Anorexia
• Part IV: Extending Activity Anorexia to Humans
• Part V: Clinical Observations and Implications of Activity Anorexia
• Author Index
• Subject Index