Obesity has emerged as a significant threat to public health throughout the developed world. The World Health Organization defines overweight as a body mass index of 25.0 to 29.9 kg/m2 and obesity as a BMI of 30.0 kg/m2 or greater.1 Nearly two-thirds of Americans are overweight or obese according to these criteria.2 Numerous health problems, including diabetes, cardiovascular disease, arthritis, and cancer, are associated with obesity. In addition, overweight and obese persons are more likely than their normal-weight peers to have a variety of psychiatric disorders.
In this review, we summarize associations between obesity and psychiatric disorders. We then discuss potential causal pathways, behavioral treatment for obesity, and ways in which psychiatric disorders can complicate obesity treatment. Finally, we provide recommendations for addressing these complications. Several studies cited in this review are based on data from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). The findings from the survey are summarized in the Table.
Epidemiological studies support positive associations between BMI and mood disorders.3-5 A recent study using NESARC data found increased odds of mood disorder symptoms—including major depression, dysthymia, and manic and hypomanic episodes—among obese and extremely obese persons compared with their normal-weight counterparts.5 Obese individuals were 1.5 times more likely than normal-weight individuals to report lifetime or past-year mood disorder; extremely obese persons were twice as likely. Anxiety disorder rates were elevated not only in the obese and extremely obese but also in those who were only moderately overweight (odds ratio [OR], 1.19 - 2.60). Lifetime and past-year prevalence of generalized anxiety disorder, panic disorder without agoraphobia, and specific phobia were elevated among individuals classified as overweight and obese.5 A greater likelihood of depression and anxiety disorders with increasing BMI has also been observed in epidemiological studies carried out in other countries, including Germany, New Zealand, France, and the Netherlands.4,6
Relationships between elevated body weight and affective disorders appear stronger in women than in men. Obesity was associated with mood and anxiety disorders in both men and women in 1 study, but overweight predicted increased odds of mood and anxiety disorder in women only.3 Other studies have found obesity to be related to depression in women but not in men.7 There is even some evidence that overweight and obesity may be associated with a lower likelihood of attempting or committing suicide among men, although increased BMI is associated with a greater likelihood of suicidal ideation among women.7,8
Because studies to date are cross-sectional, causal pathways between obesity and mood and anxiety disorders have not been identified. It is likely that pathways are bidirectional. Weight-based discrimination is widespread, and being a target of discrimination can lead to anxiety and depression.9,10 Weight dissatisfaction is more prevalent among women than men, and women are more likely than men to face weight-based discrimination.11,12 Concerns that they will be scrutinized or judged based on weight may contribute to social anxiety in overweight and obese women. In fact, overweight and obese women are at increased risk for social phobia, but BMI is not associated with the likelihood of social phobia among men.3
Mood and anxiety disorders can lead to weight gain by interfering with healthy eating or regular exercise.13 Eating may have an anxiolytic effect, although overeating in response to stress varies between individuals.14,15 Women are more likely than men to eat in response to negative emotions, and women with mood disorders are more likely than men to report increased appetite as a symptom of depression.3,16
Associations between obesity and mood and anxiety disorders may arise from effects of stress on the hypothalamic-pituitary-adrenal (HPA) axis, which responds to stress by releasing cortisol and other hormones that modulate sympathetic nervous system activity. Under conditions of chronic stress, HPA axis activity becomes dysregulated, a state that has been implicated in depression and anxiety disorders as well as in obesity.17 Future prospective studies can further clarify the direction of relationships between obesity and affective disorders.
Associations with substance use disorders
Epidemiological studies of relationships between obesity and substance use disorders yield inconsistent findings. Petry and colleagues5 found higher rates of lifetime alcohol use disorders among overweight, obese, and extremely obese individuals (OR, 1.12 - 1.33). However, when men and women were examined separately, only men showed a positive association between BMI and lifetime alcohol use disorders.18 BMI was not significantly related to lifetime alcohol use disorders among women, but there was a negative relationship between BMI and past-year alcohol use disorders among women. Studies conducted in the US and Germany found obesity to be associated with a decreased likelihood of past-year alcohol use disorders, but these results have not been replicated in other countries.6,19
Significant associations between BMI and illicit drug use disorders have not been identified. However, epidemiological samples include few persons with drug use disorders because of low population base rates.5
Limited evidence from clinical samples appears to support an inverse relationship between current substance use disorders and obesity. Persons who seek bariatric surgery for obesity report relatively high rates of lifetime substance use disorders but very low rates of current substance use disorders. This suggests that abstaining from addictive drugs could contribute to obesity.20 Other studies find inverse relationships between BMI and past-year alcohol and marijuana use among women seeking weight loss treatment.21,22 Among individuals with bipolar disorder, there is an inverse relationship between overweight/obesity and substance use disorders.23
Compulsive overeating and addictions to alcohol and other drugs appear to share common psychological and physiological underpinnings. Intake of food or drugs is reinforcing and activates reward circuits in the brain, causing the release of dopamine.24 The reward response to palatable food encourages eating, thus promoting survival; however, substances of abuse activate the system as well.25 Acute substance use leads to increased concentrations of dopamine in the brain. With chronic excessive use, however, the number of dopamine receptors declines, which leads to an eventual reduction in dopamine activity.24 A similar process may occur with overeating.
Wang and colleagues26 used positron emission tomography (PET) to compare concentrations of dopamine D2 receptors in the brains of extremely obese and normal-weight individuals. Obese individuals had significantly fewer D2 receptors than normalweight individuals. Among the obese individuals, D2 receptor concentration declined as body weight increased.26 These findings suggest that overeating, like substance use, may initially stimulate dopamine activity but eventually leads to down-regulation of dopamine receptors and a reduction in dopamine activity.
However, some authors have postulated a preexisting "reward deficiency syndrome" that predisposes one to compulsively engage in rewarding activities, including substance abuse, overeating, gambling, and sexual addiction behavior.27 Variations in genes that govern expression of dopamine D2 receptors lead to individual differences in receptor density. Individuals with fewer D2 receptors are less sensitive to subtle rewards and more prone to anxiety, anger, and dysphoria, which leaves them vulnerable to overindulging in rewarding behaviors in an effort to alleviate negative emotions.27
Overeating may thus be one of several behaviors used to compensate for the blunted reward effects of a hypoactive dopamine system. If that is the case, individuals examined by Wang and colleagues26 may have become obese because of a shortage of dopamine receptors rather than a loss of receptors because of overeating. Although there is evidence for a common pathway to obesity or drug addiction, the lack of consistent associations between obesity and substance use disorders in epidemiological samples suggests that any relationship between the two is complex.
Associations with other psychiatric disorders
Obesity is associated with several personality disorders in the NESARC sample.5 Antisocial, avoidant, obsessive-compulsive, paranoid, and schizoid personality disorders are all more prevalent among the obese and extremely obese than in normal-weight persons (OR, 1.31 - 2.55). In addition, extreme obesity is associated with a greater likelihood of dependent personality disorder (OR, 3.04). Antisocial personality disorder (ASPD) is significantly associated with BMI among women.28
Obesity has been associated with elevated rates of attention-deficit/hyperactivity disorder (ADHD).29,30 Children with ADHD and other disruptive behavior disorders are heav-ier than their peers without behav-ioral disorders and are likely to remain overweight into adulthood.31 Impulsivity associated with ADHD may thus contribute to overeating and obesity.
Schizophrenia is not associated with obesity after controlling for other variables.32 However, treatment with antipsychotic medications—particularly olanzapine and clozapine—can lead to substantial weight gain in some patients.32,33
Overall, the accumulated data on obesity and psychiatric disorders indicate that obese persons may face a variety of mental health problems in addition to the physical health problems that often accompany obesity.
Behavioral treatment for obesity
In light of the increasing prevalence of overweight and obesity in the general population and elevated prevalence among individuals with a variety of psychiatric disorders, psychiatrists frequently encounter patients who are overweight or obese. They are also quite likely to deal with patients who are experiencing weight gain in response to psychiatric medications.34 There is evidence that most physicians, including psychiatrists, have not received adequate training to counsel patients regarding obesity and options for treatment.35
Behavioral treatments for obesity generally include 3 components: dietary change; increased physical activity; and behavior therapy techniques, such as goal-setting, selfmonitoring, stimulus control, and behavioral contracting.36 In addition to weight loss itself, a goal of behavioral interventions is to introduce lifestyle changes that increase the likelihood that weight loss will be maintained.37 A typical behavioral weight loss program includes 12 to 16 lessons that cover specific strategies, such as recording daily food and calorie intake, avoiding triggers for unhealthy eating, increasing physical activity, obtaining social and family support, and modifying thoughts and emotions that undermine weight loss.38 Behavioral interventions generally result in weight losses of about 8% to 10% of initial body weight.39
Effect of psychiatric disorders on obesity treatment
Patients with comorbid obesity and psychiatric conditions may have difficulty with adhering to weight loss treatment recommendations. Depression or anxiety may interfere with the ability to adopt new behaviors—particularly those that require effort, such as preparing healthier meals or exercising. There is evidence that weight management patients with major depressive disorder lose less weight than their counterparts without depression.40 Poor impulse control associated with ADHD and ASPD can undermine self-control efforts as well.28
Patients who struggle with overweight and obesity may be reluctant to take medications that will further contribute to weight gain, or they may discontinue treatment prematurely if weight gain occurs.41 Sensitivity to these concerns can allow psychiatrists to anticipate challenges and barriers to effective treatment of psychiatric conditions. Bariatric surgery is becoming an increasingly popular treatment for severe obesity. Psychiatric evaluations to assess patients' ability to adhere to the behavioral changes required to benefit from surgery are an important part of the treatment process.42
Treating obese patients with psychiatric disorders
Behavioral assessment of obese patients can identify psychiatric conditions that might interfere with treatment.43 Experts recommend treating depression before starting patients on a weight loss program, although there is also evidence that successful treatment of obesity can lead to significant improvement in mood.34 Exercise can improve mood, and it is a vital component of a successful weight loss intervention. Thus, introducing exercise during treatment for depression can give patients a head start on improving health before they begin a weight loss program.
Patients with anxiety disorders may become alarmed by the physical sensations they experience during exercise. Many require a gradual increase in exercise intensity to learn that heart rate and respiration will return to normal after exertion. Anxious patients may also need encouragement and even gradual exposure to overcome avoidance of behaviors that trigger anxiety, such as weighing themselves or keeping records of weight or food intake.
Patients with ADHD are likely to have difficulty adopting many weight loss strategies, particularly those like self-monitoring of food intake that rely on the ability to keep organized records and make entries on a regular basis. It may be necessary to work with these patients to develop routines for planning meals, finding time for regular exercise, and organizing food diaries and other self-monitoring materials.
Concern about the increased prevalence and negative health effects of obesity continues to grow. Greater understanding of psychiatric comorbidity may facilitate the development of more effective prevention and treatment interventions.
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