Behavioral determinants of obesity have been widely studied in the field of psychology, leading most to conclude that it is a complex condition that is difficult to treat with long-term success. This chapter reviews the most common theories about psychological causes of obesity, the co-occurrence of obesity and common mental disorders, and psychological treatment options for obesity and binge-eating disorder (BED). Suggestions for assessment and treatment planning are provided to help physicians determine the presence of underlying psychopathology or problematic behavior patterns and to work with their obese patients to find a program best suited to their individual psychological needs.

It is widely accepted that the etiology of obesity is multidetermined. In addition to genetic, physical, environmental, and cultural/sociological factors, psychological research has focused on individual characteristics such as personality, systems of reinforcement, cognitive processes, and developmental history, as well as the interplay of all of these factors. Decades of research have focused on the psychology of overeating and whether obese individuals differ from their nonobese counterparts in their eating behavior.¹ In the following section, the most studied theories about overeating in obesity are presented along with discussion of their current research support.

A commonly held view is that obese people are more likely to engage in emotional eating, using food to manage distressing or overwhelming affect. The psychosomatic hypothesis, first put forth by Kaplan and Kaplan² suggests that obese individuals likely learned as children to overeat as a way to self-soothe when anxious. Their subsequent weight gain further increases negative affect, which then leads to more overeating and obesity. The psychoanalyst Hilde Bruch³ further hypothesized that for these individuals early developmental trauma, such as poor infant-caregiver attunement, interferes with the child’s ability to distinguish between internal sensations of hunger and uncomfortable emotional states. The child therefore misinterprets emotions such as sadness and anger as hunger and will overeat to regulate these feelings.³

In their 2002 review, Canetti, Bachar, and Elliot⁴ concluded, that for both obese and nonobese people, the presence of negative emotions (e.g., anger, sadness, boredom) leads to increased food consumption. Some research indicated that positive emotions (e.g., joy) can also increase food intake for both obese and nonobese individuals; however, the support for this conclusion is not as robust.⁴ Canetti et al.⁴ stated that the psychosomatic theory of obesity has received enough research support to conclude that obese individuals and dieters (obese or normal weight) are more likely to engage in emotional eating. A more recent review of binge eating and overeating in laboratory settings further supported the role of negative affect as a trigger for overeating for obese individuals, and even more strongly so for those with BED.⁵

In the late 1960s and early 1970s, Schacter argued against the psychosomatic model by developing his externality theory of overeating; he suggested that the sensory aspects of the food itself, such as sight, taste, and smell, lead obese people to overeat, and that perhaps differences in hypothalamic function for appetite were to blame.⁶ Researchers have since challenged externality theory, positing no difference between obese and nonobese individuals’ tendency to rely on internal or external factors to guide their eating behavior (Moskovich et. al., 2011; Canetti et. al., 2002).^1,4 Stroebe et al. suggested that both distressing affect and external cues seem to drive overeating for obese individuals, citing several experimental studies demonstrating how stress can trigger overeating for obese individuals, but only when the food is tasty and appealing.⁷

Nisbett developed set point theory as an attempt to further Schacter’s hypothesis about the role of the hypothalamus in overeating.⁸ According to his theory, we all have a set point for our weight, which our body will attempt to maintain by altering metabolism and eating behavior. Thus, when an obese individual loses weight through dieting, the individual’s metabolism will slow, and the person will experience increased sensitivity to external cues, causing the person to overeat so that his or her body can return to its set point.⁸ Although set point theory has been widely dispersed and accepted in popular culture, it has been challenged by some longitudinal studies as well as the data that obesity rates have dramatically increased over the past several decades throughout the industrialized world.⁷

Indeed, more recent neuroimaging research has suggested that it is not the hypothalamic system that drives overeating behavior, but rather neurological centers for reward and pleasure.⁷ Several studies using functional magnetic resonance imaging (fMRI) technology have demonstrated that obese individuals show increased neurological reactivity regions that mediate emotional responses to food cues. There is also some evidence that weight gain decreases this receptivity, so that individuals would need to consume even more to obtain the same neurological reward experience.⁷

Another set of research on the psychological causes of obesity has focused on the role of cognition and beliefs. Herman and Mack described the disinhibition effect in their theory of overeating; they theorized that restrained eaters who believe that they violated their diet, whether or not they actually did, are more likely to subsequently overeat.⁹ Indeed, there is strong research support demonstrating that restrained eating actually puts individuals at risk for overeating, especially in the presence of exacerbating factors such as stress, distraction, negative emotions, and depression.^1,7,10 While the state of deprivation itself may induce more intense cravings for food, this phenomenon may also be due to thoughts that occur in reaction to perceived diet violations, such as, “I’ve blown it now; might as well keep eating.”

Stroebe et al. recently offered a goal-conflict model as an attempt to explain the difficulties chronic dieters have in regulating their eating.⁷ These authors questioned whether set point or other physiological theories are the reason why dieters fail and tend to return to overeating patterns. Rather, they suggested that dieting is a “self-control dilemma” between two seemingly incompatible goals: food enjoyment and weight control. When dieters chronically inhibit their eating enjoyment goal, they become even more sensitive to the food-rich environment endemic to modern industrialized culture. These authors posited that intrusive thoughts about overeating tax the greater cognitive resources required to maintain a weight control goal, which ultimately leads the individual to pursue the eating enjoyment goal instead.⁷

Personality traits that correlate highly with obesity have also been extensively studied, particularly with regard to the Big 5 personality traits of neuroticism, conscientiousness, agreeableness, extraversion, and openness to experience. Researchers have found that higher levels of conscientiousness are associated with lower obesity, especially for women.^11,12 Higher levels of agreeableness have predicted higher obesity for men, and higher levels of neuroticism have been associated with lower obesity for men, but had no correlation with obesity for women.¹¹ Sutin et al. found that high neuroticism and low conscientiousness were associated with more weight fluctuations across one’s life, and that low agreeableness and high levels of trait impulsivity were associated with higher body mass index (BMI).¹² Sutin et al. suggested that the association between personality factors and obesity are likely mediated by other factors, such as greater physiological reactivity to stress.

Binge-Eating Disorder

There is evidence to suggest that 25%–45% of obese individuals treated in weight control programs report binge eating.¹³ An episode of binge eating is most commonly defined as eating a large quantity of food (much larger than what most people would eat) in a discrete amount of time. The context in which the binge occurs is important, so, for example, a reported “binge” during a holiday celebration should be interpreted as normative for that situation.¹⁴ The episodes must also occur in a brief amount of time (typically less than 2 hours), so that although the total calories consumed may be equivalent, snacking throughout the day, or “grazing,” is not considered a binge.¹⁴ A second defining component is a subjective feeling of “loss of control” during the binge.¹⁴ Finally, if the binge is followed by compensatory behaviors, such as purging or taking laxatives, bulimia nervosa becomes the likely diagnosis.¹⁴

The existence of BED as a psychiatric diagnosis is recent; in prior editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM), it was included as a provisional diagnosis. BED was finally included in the latest edition of the DSM (DSM-5), published in 2013. Diagnostic criteria for the disorder are listed in Table 8-1. To meet the diagnosis of BED, patients must engage in binge-eating episodes at least once a week for 3 months or longer. These episodes must occur in a 2-hour window, and the amount consumed must be significantly greater than what is normally consumed “under similar circumstances.” The binge-eating episodes must also be accompanied by a sense of lack of control. The DSM-5 reports a 12-month prevalence of BED among US adults at a little over 2% (1.6% for females and 0.8% for males).¹⁴

It is important to note that not all binge eaters are obese, and not all obese people are binge eaters. It has been suggested that normal-weight binge eaters may compensate between binges by engaging in more dieting behavior than obese binge eaters.¹³ Regarding the differences among obese individuals who binge eat versus obese individuals who do not, some research evidence suggests that obese binge eaters experience less perceived control over eating, more fear of weight gain, more dissatisfaction with weight, and more food and weight preoccupation.¹³ Laboratory studies of binge-eating behavior (for both obese and normal-weight subjects) have demonstrated that when offered a buffet of various food options, binge eaters eat a larger quantity than their weight-matched counterparts, and they tend to choose foods that are high in sugar and fat.^13,15

For bulimic individuals, a restrictive diet frequently precedes a binge; however, research on the antecedents of binge eating in obese individuals is not as clear.^15,16 Binge eating has been associated with weight cycling, but causality has not been determined.¹⁵ Binge eating in obesity is also concurrent with a number of psychiatric disorders, particularly depressive disorders, panic disorders, and personality disorders,^13,15 suggesting that binge eating may be a mechanism to manage mood and anxiety for individuals with poor affect regulation. Indeed, Leehr et al.’s recent meta-analysis of laboratory studies provided strong support for the affect regulation model of binge eating for individuals with BED.⁵ Finally, binge eating has also been significantly correlated with a history of physical or sexual abuse.¹³

Depression

Early research on the correlation between obesity and depression showed only weak associations; however, more recent studies have demonstrated a moderately significant link between the two, especially for women.¹⁷ Other moderating factors include age, socioeconomic status, and race. Specifically, young Caucasian women who are of higher socioeconomic status are more likely to be depressed if obese.¹⁸

Much of the literature on this topic has had to grapple with a “chicken-versus-egg” type dilemma. Specifically, does depression lead to obesity, does obesity lead to depression, or are they reciprocal influences on each other? There is some evidence supporting all three pathways; however, obesity as a risk factor for depression seems to have a stronger research base, especially when high levels of body dissatisfaction are reported.¹⁸ The role of bullying and teasing in the connection between obesity and depression has not been studied extensively; however, some studies have demonstrated that obese children and adolescents who are victims of bullying are more likely to become depressed.¹⁸ Another moderating factor in the correlation between obesity and depression concerns the impact of decreased mobility and other physical functioning. Only a few studies have examined this relationship, but they have indicated that increased health problems and difficulties with daily functioning increased negative affect.¹⁸

The question of whether depression causes obesity was addressed in Blaine’s meta-analysis of 16 longitudinal studies, combining 33,000 participants.¹⁹ The results suggested that depressed individuals are significantly more likely to become obese at follow-up than their nondepressed counterparts. This effect was even greater for depressed adolescent girls, who were found to be 2.5 times more likely to become obese than their normal-weight peers over time.¹⁹ Finally, several researchers have put forth a bidirectional hypothesis of the relationship between obesity and depression, suggesting that the chronic dieting of obese individuals and the social stigma they experience cause depression, and the lack of exercise, negative thoughts, emotional eating, and social isolation that are characteristic of depression can worsen obesity.^18,19

Other Psychiatric Disorders

Obesity has also been found to correlate highly with other mental disorders. A New Zealand study found a strong correlation between obesity and anxiety disorders, especially posttraumatic stress disorder,²⁰ leading the researchers to speculate that this subgroup may be more susceptible to emotional eating to modulate anxiety. A Canadian study likewise found obesity to be positively associated with a lifetime prevalence of mood or anxiety disorders.²¹ Their results further indicated that, independent of the effects of these psychiatric disorders, obese individuals are more likely to consider and attempt suicide.

There is also a high incidence of obesity for individuals with serious mental illness, such as schizophrenia.²² Increased appetite and weight gain are common side effects of antipsychotic medication.²³ Studies have also found that those with schizophrenia have a greater tendency to engage in binge eating and night eating, and they consume more calories than non–mentally ill controls.²⁴ Lundgren et al. found that their sample of 22 obese patients with schizophrenia were more likely to engage in overeating behavior in response to the sensory qualities of food and were more likely to continue eating after feeling full.²²

Less studied than the psychological causes and correlates of obesity are the psychological consequences of living in an obese body. There is some evidence suggesting that obesity has negative consequences on self-esteem, particularly for women.¹ This seems to be worse for individuals who were teased as children and adolescents and for those with repeated failures at dieting.¹ Wardle and Cook’s meta-analysis of the research on the psychological effects of obesity on children and adolescents did find moderate support for increased levels of body dissatisfaction among obese children; however, the results were weak and mixed with regard to depression and low self-esteem.²⁵ The authors warned professionals against the assumption that obesity causes psychological maladjustment, as many obese children seem to show resilience in the face of weight discrimination.

It is clear from the literature that there are numerous psychological pathways to obesity. Health care professionals are therefore cautioned against assuming typical etiological influences or even unitary causality within individual patients.²⁶ Rather, practitioners should adopt a sensitive and curious stance when working with obese patients to best understand the unique cognitive and emotional patterns that may be underlying their eating and exercising behavior. Health care professionals who assume a stereotypic etiology for their individual patients (e.g., that all obese patients are depressed, or emotional eaters, or nonexercisers) without directly inquiring about these habits are not only doing these patients a disservice but also may be contributing to our culture’s overall weight-based discrimination.

Indeed, several studies have revealed the implicit biases that health care providers often harbor toward their obese patients. Klein et al. found their sample of 400 physicians associated obesity with poor hygiene, noncompliance, hostility, and dishonesty.²⁷ Similarly, Price et al. found that two-thirds of their family physician respondents stated that their obese patients lacked self-control, and 39% described them as lazy.²⁸ Other studies of health care professionals such as nurses and medical students yielded similar results, demonstrating that there exists substantial weight-related bias within the medical profession.²⁹

This stigma within the medical field often leads to poor practice. A study of hundreds of physicians of various specialties revealed that the majority were uncomfortable discussing weight management with their obese patients, and many avoided the topic altogether.³⁰ Whether it is implicitly or explicitly expressed, the discrimination some obese patients feel from their medical providers can have a negative impact on their decision to seek care. Very overweight women were found to be significantly less likely to have yearly pelvic exams, especially when they reported negative body image.³¹ Likewise, these researchers found that 17% of the physicians they surveyed were reluctant to perform pelvic exams on very obese women, and that number jumped to 83% when the women were also reluctant.³¹ Other studies have found that obese women often delay or cancel physician appointments because of their embarrassment about their weight, fears of getting weighed, and prior negative experiences when discussing their weight with physicians.^32,33