Weight Regulation Research Paper

Body size usually is characterized in terms of body mass index (BMI) (computed as the ratio of weight measured in kilograms to the square of height measured in meters). A BMI below 18.5 is defined as underweight, from 18.5 to 24.9 as normal weight, from 25 to 29.9 as overweight, and over 30 as obese. The predominant weight disorder in the industrialized world is obesity and now almost one in five adults are obese, and twice as many are overweight (Seidell and Rissanen 1998). Anorexia nervosa and bulimia nervosa fall at the other extreme of weight disorders, and while they don’t match the prevalence of obesity, together they represent the most common psychiatric diagnoses for young women today (Hoek 1995).

1. Weight And Weight Control

Weight control problems appear to be very different at the two extremes. Most obese people are aware of their weight problem and try to regulate their food intake, but often they find it impossible to exert enough control, or to maintain control over a long enough period, to achieve a normal body weight. In contrast, patients with eating disorders appear to exert excessive control over their body weight, successfully defying biological and social pressures to eat. In between the two extremes lies the normal-weight population. At one time it was assumed that these would be the ‘normal’ eaters, that is, not worried about weight and regulating their energy balance without any deliberate effort. However, this view is looking increasingly questionable. In Britain, for example, the proportion of the population who are obese has doubled since the mid-1980s, and concerns about weight control are widespread, even among the normal-weight, suggesting that weight regulation is neither effortless nor effective. The normal-weight population probably includes a minority who maintain a normal weight without deliberate effort, a larger group (most often men) whose weight slowly increases over time, but who make little attempt to regulate it, and the largest group (in which women predominate) who are chronically attempting to control their food intake in order to regulate their weight closer to the contemporary ideals for body shape.

Research into psychological aspects of weight regulation is predominantly in three areas: (a) the psychological processes leading to the development of eating disorders, (b) the psychological processes leading to obesity, and (c) the causes and consequences of dietary restraint.

2. Weight Regulation In Eating Disorders

Psychological research on eating disorders has a long history dating back to observations in the eighteenth century that extreme loss of weight could have a psychogenic origin. More recently, the formal psychiatric diagnosis of anorexia nervosa was established, with key features being extreme weight loss, a morbid fear of fatness and deliberate restriction of food intake to achieve a low body weight. Bulimia nervosa was characterized later as a distinct but related disorder, sharing a morbid fear of fatness, but with an eating pattern consisted of binge eating followed by self-induced vomiting or purging to achieve weight control (Garfinkel 1995). Much of the psychological research on eating disorders has been concerned with the origin of fear of fatness, and although there are a number of aetiological theories (see Brownell and Fairburn 1995), the most widely accepted view is that eating disorders emerge in response to the cultural pressures for a slim physique in vulnerable individuals. Recent evidence suggesting that there is a genetic element to eating disorders is consistent with the idea that there is an inherited predisposition which depends upon events in the environment to emerge as a disorder (Bulik et al. 2000).

2.1 Weight Control In Anorexia Nervosa

From the perspective of weight regulation, the most interesting question is how anorexic patients successfully maintain a low body weight, when everyone else finds it so difficult. There has been surprisingly little progress in understanding this process. Implicit in the etiological accounts is the idea that eating disordered patients are exceptionally highly motivated. Weight gain is so much feared that any degree of suffering is acceptable to avoid it. Cognitive factors may play a part, with clinical evidence indicating that anorexic patients use an elaborate array of cognitive strategies to render the idea of food and eating undesirable. A third factor is personality; anorexic patients tend to be both perfectionist and persevering, either of which might facilitate weight control. However, none of these factors appears to capture the secret of the extraordinary, albeit pathological, weight control capacities of patients with anorexia nervosa.

2.2 Weight Control In Bulimia Nervosa

The phenomenology of bulimia nervosa illustrates a different weight control strategy, involving giving in to the desire to eat during binge episodes, but avoiding the consequences of eating (weight gain) by inducing vomiting (Garfinkel 1995). Many bulimic patients start inducing vomiting as a temporary means of gaining control over their weight, but in practice both the sense of loss of control and the size of the binges, often increase. One explanation for this is that appetite is modified by the postingestional calorific consequences of feeding, and if these are attenuated by vomiting then appetite increases to compensate. Inducing vomiting after eating is certainly an effective strategy for weight control, but in terms of adverse psychological and physical effects, the costs usually exceed the benefits.

3. Weight Regulation In Obesity

The problem of obesity needs to be investigated on several levels in order to understand (a) why it has become so much more common over recent decades, (b) why some people are so much fatter than others, and (c) how obesity treatments could be made more effective.

3.1 The Increasing Prevalence Of Obesity

Most accounts of the shifts in obesity prevalence over time draw not on changes in social or psychological conditions, but on the combination of an environment which favors a positive energy balance and an appetite control system which evolved when the food supply was limited. There is now an abundant, highly palatable, food supply in industrialized countries. At the same time, transportation systems and mechanisation have reduced the energy demands of everyday life. If human beings evolved to store energy supplies, then it is not surprising that so many people are now overweight (Hill and Peters 1998).

3.2 Emotional Theories Of Obesity

Psychologists’ first incursions into understanding the causes of obesity at an individual level focused on underlying psychopathology, with suggestions that eating served unconscious needs. These ideas came largely from clinical observations by psychodynamically-orientated therapists. Empirical studies have shown that levels of psychopathology are no higher in the obese than the normal-weight population, and although there is evidence that severely obese adults have raised levels of depression and anxiety, this appears to be a response to the multiple handicaps and stigmatization associated with obesity (Sobal 1991). Unfortunately, popular discourse continues to equate obesity with psychological problems, leading to greater problems of stigmatisation.

3.3 Psychobiological Theories Of Obesity

This perspective was followed by psychophysiological models which combined investigations of the psychophysiology of obesity and food intake with assessments of eating behaviour. Obesity was hypothesized to be caused by low responsiveness to internal cues for satiety combined with high responsiveness to external food cues. Laboratory studies showed differences in responsiveness to food between obese and normal-weight adults, and the theory was reinforced by parallel observations on animal models of obesity (Schachter 1968). At around the same time, the idea of a ‘set-point’ for weight was put forward, suggesting that each individual had a particular level of fat stores which was defended by up-regulating appetite if they were depleted, and down-regulating it if they were filled. At the time, the ‘fact’ that most people had a fairly stable body weight over their lifetime was adduced as support for the set-point theory. Obese people were hypothesized to have a higher than normal set-point, and would show abnormalities of appetite when they lost weight to below their own set point weight. However, subsequent research suggested that it was not obesity per se nor even weight loss which was linked with abnormal appetite, but deliberate weight control (Herman 1978). Obese people who were not bothering with weight control appeared to respond normally to food and satiety cues, while normal-weight dieters showed a pattern of responses which resembled the dieting obese. These observations led to tremendous interest in research on the effects of dietary restraint (see below) but a period of relative stagnation in research into the psychological process in obesity.

3.4 Psychological Treatment For Obesity

Psychological treatments for obesity developed primarily from a behavioral analysis of the problem. Obese people were hypothesized to have abnormal eating habits, which tended to promote a positive energy balance. The earlier formulations of the so-called ‘obese eating style’ incorporated rapid eating (preventing the normal processes of satiation emerging during the course of the meal), chaotic eating (eating in a wide range of different places), as well as the idea of externally-cued eating. None of these ideas survived rigorous examination, but in the meantime, they had proved to be useful as the basis for behavioral treatment. Treatment incorporated stimulus control (ensuring that exposure to cues for eating were controlled), slow eating, and limiting the number of places in which eating occurred, along with the standard behavioral procedures of self-monitoring, goal-setting, and self-reinforcement. The first results were very positive (Wing 1998). In time, cognitive elements were added to the programs, including modifying self-defeating cognitions and dealing with the lapse-relapse sequence. Cognitive behavior therapy (CBT) is now regarded as the gold standard for obesity treatment, and CBT training has been identified as a necessity for other health professionals. However, it remains true that many patients drop out of treatment, few lose substantial amounts of weight, and many regain the weight that they have lost, so there is still a great deal of scope for improvement.

Current thinking on obesity treatment has recovered from a period of despondency about treatment efficacy by acknowledging that weight losses are likely to be relatively small, and taking account of the fact that even small weight losses can have significant benefits for health (Allison and Pi-Sunyer 1995). There is a recognition that obesity is a chronic disorder requiring continuing care. There is a renewed interest in the psychological aspects of obesity, particularly the problems of body image and social stigmatisation, and some suggestion that treatments which offer a broaderbased approach produce better overall outcomes on health and wellbeing. Most importantly, the difficulties which almost all obese people experience in losing weight has led to greater interest in prevention, in the hope that interventions could be initiated before overweight is established and health and well-being are compromised.

4. Weight Regulation And Dietary Restraint

While health risks associated with overweight emerge only at a BMI of over 25, many women aspire to a much slimmer figure as promoted across all forms of media (Brownell 1991). In search of the slim ideal, many women, and even pre-adolescent girls, try to restrict what they eat in order to control their size. The concept of dietary restraint was put forward in 1975, to describe an eating pattern which consisted of attempted control over eating, interspersed with regular failures of control (Herman 1978). Several psychometric measures have been developed, starting with the original Restraint Scale, but subsequently distinguishing the concepts of attempted control (now often called restrained eating) and failures of control (called counter-regulation or disinhibition). A raft of experimental studies showed that restrained eaters were less responsive to satiety, more responsive to palatability, and more likely to show over-eating in response to negative affect. Binge eating was also conceptualized in relation to restraint, following the realisation that most binge eaters were also chronic dieters (Wardle and Beinart 1981). These observations turned existing ideas on their head in suggesting that attempts to regulate food intake might be the cause of, and not simply a response to, problems of eating control.

4.1 Restraint And Inhibition

The association between restraint and regulatory problems is now well-established, but there is still uncertainty about the mechanism, and especially about why restrained eaters should ever actually eat more than unrestrained eaters. The cognitive model of restraint proposes that after a high calorie preload (in the laboratory) or a dieting transgression (in everyday life), the dieter ‘reasons’ that they might as well take advantage of the situation and leave dieting until tomorrow. The psychobiological model suggests that after a long history of imposed cognitive control, in which normal biological controls have been overridden and food intake patterns are chaotic and irregular, sensitivity to satiety or hunger signals becomes blunted and learned patterns of hunger and satiety are disrupted. The emotional model suggests that the dieter copes with negative emotional states with dissociation, and as part of this, loses contact with their restrictive intentions. There is some evidence for each of these processes, but as yet there have been no definitive studies that distinguish between them.

4.2 Implications For Treatment

When the paradoxical effects of dietary restraint were invoked to explain binge eating in bulimia, this led to cognitive-behavioral treatments focusing not only on helping bulimic patients to take a more positive view of their body, but also to relinquish rigid dietary restraint. Likewise in obese binge eaters, loss of control over eating has been interpreted as a consequence of strict dieting. This view was supported by the weight history of many obese patients, among whom any period of losing weight on a diet seemed to be followed inexorably by regain to higher than initial weight, as well as by the poor outcome of most obesity treatment programs, where long-term follow-up showed that many patients ended up fatter than when they had started. Caution was counseled in offering conventional dietary treatment to obese binge eaters, and some psychologists promoted so-called ‘undieting’ treatments, where obese patients could be helped to stop their long-established habits of trying (and failing) to restrict what they ate (Goodrick et al. 1998).

4.3 Deliberate Weight Control

Recently, there have been signs of a renaissance of interest in deliberate weight control in the face of the epidemic scale of the obesity problem. Evidence is emerging that dieting is not inexorably associated with problems of control (Howard and Porzelius 1999). Among the obese, binge-eaters have not been found consistently to be more restrained than nonbingeeaters, and contrary to expectations, obese binge-eaters fare no worse than nonbinge-eaters in conventional dietary treatments. In the normal-weight population, individuals who are either dieting or at least ‘watching their weight’ appear to consume healthier diets than nondieters, and probably gain less weight over time. There has also been a realization that most research on dietary restraint in the normal population was based on comparisons between restrained and nonrestrained eaters, but since restrained eaters probably become restrained because they were susceptible to weight gain, the causal processes may be more complex than was thought.

On present evidence it seems likely that restraint can increase the risk of loss of control, but there may be riskier and less risky forms. Flexible restraint has been associated with better weight control than rigid restraint. Eating regimens with regular meal patterns and a balanced nutrient intake are probably better than short-term drastic restriction. Negative body image is very often the motive for attempts at weight loss, but may in itself increase the difficulty of controlling weight, so interventions which improve body image could facilitate weight control. Higher levels of physical exercise consistently are associated with better weight control, both in the normal population and in maintaining weight loss after treatment, and deserve a higher profile in psychological treatments.

5. The Future

In recent years one of the most influential developments has been the observation that individual differences in weight are under substantial genetic control. Identical twins are highly similar in weight at all stages of life, and consistently more similar than fraternal twins. The results of twin studies are supported by adoption studies which have shown that the BMI of adoptive children is correlated strongly with the BMI of their biological parents and barely at all with the adoptive parents’ BMI. These findings have important implications for psychological research into weight control, pointing to the need to investigate eating behavior in ‘at risk’ populations (Faith et al. 1997). If shared family environment plays much less of a part in determining weight than has been believed, then this raises the question of what aspects of the individual environment promote weight regulation and control.

In the past, psychological research on weight regulation has tended to run a parallel course to research on biological processes, but the best progress is likely to come from integrative approaches in which the control of appetite and weight is seen as the product of a network of interactions among the elements from different domains. There have been tremendous advances in understanding the biological basis of obesity, and a growing interest in new pharmacological treatments, all of which offer great opportunities for psychological research as we seek to understand how biology and behavior are integrated to achieve weight regulation.

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