Obesity is a complex multifactorial chronic disease that develops from the interaction between genotype and the environment. Obesity in individuals with mental disorders such as schizophrenia has been attributed to various factors, including a sedentary lifestyle, poor nutritional choices or lack of access to healthy foods, the effects of both the mental disorder itself and the medications used to treat it, and lack of access to adequate preventative medical care.

Excess body weight increases the risk for many medical problems, including type 2 diabetes mellitus, coronary heart disease, osteoarthritis,  hypertension,  and gallbladder disease.  Abdominal or visceral obesity is particularly associated with increased risk for insulin resistance and/or the metabolic syndrome and for type 2 diabetes mellitus, and persons with schizophrenia have greater visceral adiposity than healthy individuals.

The clinical problem of obesity has become more apparent with the availability of second-generation,  or ‘atypical’,  antipsychotics.  Their advantage over the older ‘neuroleptics’ have principally been in their lower propensity for extrapyramidal side effects, including tremor, rigidity, and akathisia. However, one of the most troubling adverse effects of the second-generation antipsychotics is treatment-associated weight gain. The second-generation antipsychotics available today differ in their propensity for weight gain and the degree of weight change can also vary from patient to patient.

Efficacy may also differ from drug to drug, and patient to patient, making medication selection and monitoring for weight gain a complex issue and can give rise to significant therapeutic dilemmas. Moreover, obesity can be an obstacle to adherence to medication, as evidenced by a mail survey of persons with schizophrenia where BMI status and subjective distress from weight gain were predictors of noncompliance.

This chapter addresses what the clinician can do to ameliorate the problem of overweight and obesity observed in patients with mental disorders, particularly schizophrenia.  When using antipsychotics,  especially those most associated with weight gain, ongoing monitoring is essential. Certain patients, such as children, adolescents, and those with their first episode of schizophrenia, are at higher risk for weight gain, even when using the second-generation antipsychotic medications that are ordinarily considered as ‘weight-neutral’. Early monitoring can identify early weight gainers; these patients are at significant risk for substantial weight gain. Lifestyle interventions are crucial when weight gain occurs and switching antipsychotic medication is not a viable option. Adjunctive medications for weight loss can be considered but randomized clinical trials for this intervention have generally not been encouraging.

Definitions

Body mass index (BMI), calculated as the quotient of body weight (kg) divided by the square of height (m),  is commonly used to assess body weight.  On-line calculators for BMI are readily available (for example,  the website from the Centers for Disease Control and Prevention, http://www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi).

Overweight is defined as a BMI between 25 and 29.9 inclusive, and obesity is defined as having a BMI of 30 or greater. BMI-related health risks are well established, with health risk considered ‘high’  for BMI of 30–34.9,  ‘very high’  for BMI 35–39.9,  and ‘extremely high’ for BMI greater than 40.

Alternate definitions have focused on waist-to-hip ratios or waist circumference used in the definitions for metabolic syndrome developed by the World Health Organization and the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (NCEP), respectively.

Moreover, these definitions may not apply in all ethnic groups. For example, waist circumference for Asians is generally lower, requiring a lower cut-off of 90 cm in men (instead of 102 cm in the NCEP definition) or 80 cm in women (instead of 88 cm), when assessing the prevalence of central obesity. In Japan, the definition of obesity is a BMI of at least 25, rather than the 30 used among Caucasians.

Quantitative measures of body fat have been developed, notably dual energy X-ray absorptiometry (DEXA).

Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (NCEP), respectively.

Moreover, these definitions may not apply in all ethnic groups. For example, waist circumference for Asians is generally lower, requiring a lower cut-off of 90 cm in men (instead of 102 cm in the NCEP definition) or 80 cm in women (instead of 88 cm), when assessing the prevalence of central obesity. In Japan, the definition of obesity is a BMI of at least 25, rather than the 30 used among Caucasians.

Quantitative measures of body fat have been developed, notably dual energy X-ray absorptiometry (DEXA).