DEFINITION AND ETIOLOGY

Obesity has become an important public health problem in industrialized countries throughout the world. The body mass index (BMI = weight [in kg]/height² [in m²]) is the primary measurement used to categorize obese patients (Table 1). Excess body weight (EBW) is defined as the amount of weight present in excess of ideal body weight (IBW), as determined by Metropolitan Life Tables. In 1991, the National Institutes of Health defined morbid obesity as a BMI of 35 kg/m² or higher with severe, obesity-related comorbidity or a BMI of 40 kg/m² or higher without comorbidity.¹

Table 1 Definitions of Obesity

The development of obesity involves the interactions between excessive intake, inefficient calorie use, reduced metabolic activity, a reduction in the thermogenic response to meals, and an abnormally high set point for body weight. Genetic, environmental, and psychosocial factors all contribute to this problem.

PREVALENCE AND RISK FACTORS

The prevalence of obesity in the United States has increased from 15% in 1980 to 32% in 2004.² The prevalence of extreme obesity (BMI > 40 kg/m²) is 2.8% in men and 6.9% in women. The prevalence of childhood and adolescent obesity has tripled since 1980 and, currently, 17% of U.S. children and adolescents are overweight. Obesity and morbid obesity affect women and minorities (particularly middle-aged black and Hispanic women) more than white males. However, in almost every age and ethnic group, the prevalence of overweight or obesity exceeds 50%.

Recent studies have also delineated the importance of childhood weight for influencing adulthood weight. Being overweight during older childhood is highly predictive of adult obesity, especially if a parent is also obese. Being overweight during the adolescent years is an even greater predictor of adult obesity. Obesity is now the second leading cause of preventable death after cigarette smoking, despite expenditures of over $45 billion annually on weight loss products.³

PATHOPHYSIOLOGY AND NATURAL HISTORY

Adipose tissue is primarily stored in the subcutaneous tissue and abdominal cavity. In general, females are more likely to deposit fat in the peripheral tissues and males tend to deposit fat in the abdominal compartment. As obesity develops, the size and number of fat cells increase. As fat cells grow, they release increasing amounts of cytokines (and lower amounts of adiponectin); these changes have deleterious effects on glucose and lipid metabolism and contribute to the proinflammatory state associated with obesity.

Obesity shortens the life span of those who suffer with it. The mortality rate of an individual with a BMI higher than 40 kg/m² is double that of a normal-weight individual.⁴ It is estimated that a man in his twenties, with a BMI higher than 45 kg/m² has a 22% reduction in life expectancy: 13 years.⁵ Most obesity-related deaths result from complications related to diabetes and cardiovascular disease. Worldwide, approximately 2.5 million deaths occur annually because of obesity-related comorbidities.

SIGNS, SYMPTOMS, AND RELATED DISEASES

There are more than 30 comorbid conditions associated with severe obesity. Insulin resistance and diabetes mellitus occur in 15% to 25% of obese patients. Increased abdominal fat raises the intra-abdominal pressure and contributes to gastroesophageal reflux, stress urinary incontinence, venous stasis disease, and abdominal hernia in obese patients. Fatty deposits in the liver can progress to nonalcoholic steatohepatitis (NASH) and ultimately to liver failure. Excess weight causes joint and back stress that can lead to debilitating joint disease. The low-grade inflammatory state associated with morbid obesity has been implicated in the development of vascular and coronary artery disease and the hypercoagulable state seen in these patients. Obese patients have impaired pulmonary function, particularly decreased functional residual capacity, and frequently suffer from asthma, obstructive sleep apnea, and obesity hypoventilation syndrome (pickwickian syndrome). Other comorbidities include hypertension, dyslipidemia, asthma, and sex hormone dysfunction. Obesity is associated with an increased incidence of uterine, breast, ovarian, prostate, and colon cancer and of skin infections, urinary tract infections, migraine headaches, depression, and pseudotumor cerebri.

DIAGNOSIS AND EVALUATION OF COMORBIDITIES

The diagnosis of morbid obesity is established by determining the patient’s BMI and the presence of any significant comorbid conditions. A thorough history, physical examination, and focused testing will uncover previously undiagnosed comorbidities in up to two thirds of obese patients.

Visceral, or central, adiposity is more metabolically active than peripheral fat and is associated with type 2 diabetes, dyslipidemia (elevated triglyceride and reduced high-density lipoprotein [HDL] levels), high blood pressure, and increased risk for cardiovascular atherosclerotic disease. The waist-to-hip ratio helps to identify patients with excess visceral adiposity. Women with a waist-to-hip ratio of more than 0.8 and men with a ratio of more than 1.0 are considered to have excess central adiposity that confers risk for developing the metabolic syndrome. The diagnostic criteria for the metabolic syndrome are shown in Table 2.

Table 2 Adult Treatment Panel III Criteria for the Metabolic Syndrome*

* Three or more of these criteria need to be present.

The pretreatment evaluation performed at the Cleveland Clinic is consistent with published guidelines.⁶ Because obese persons are at higher risk for cardiovascular disease, a baseline electrocardiogram should be performed. Cardiology evaluation is carried out when there is evidence of cardiac disease based on clinical symptoms or electrocardiographic findings. Chest radiography and baseline laboratory testing, including a complete blood count, chemistry panel, liver function tests, thyroid function tests, and a lipid profile, should be performed as well.

Obstructive sleep apnea frequently goes unrecognized in this patient population until a thorough history prompts further evaluation. Patients with symptoms of loud snoring, daytime hypersomnolence, or a neck circumference of 43 cm or more should undergo polysomnography and, if positive, be treated with nasal continuous positive airway pressure. Asthma and obesity hypoventilation syndrome (chronic hypoxemia, hypercarbia, pulmonary hypertension, and polycythemia) are also severe pulmonary complications of obesity and should be evaluated by a pulmonologist.

Dietary counseling and psychological testing are required for patients being referred for bariatric surgery.

TREATMENT

Lifestyle Modifications

According to the clinical guidelines published by the American College of Physicians, all patients with a BMI of 30 kg/m² or higher should be counseled intensively on lifestyle and behavioral modifications, such as appropriate diet and exercise.^7,8 An algorithm by the American College of Physicians for medically managing obesity is shown in Figure 1.⁸ The patient’s goals for weight loss should be individually determined and may encompass other related parameters, such as decreasing blood pressure or fasting blood glucose levels. When establishing realistic weight loss goals, it is important to realize that modest weight loss (10%-15%) of baseline weight is sufficient to result in health benefits.^9,10

Figure 1 Algorithm for the medical management of obesity.

BMI, body mass index.

(With permission from Snow V, Barry P, Fitterman N, et al: Pharmacologic and surgical management of obesity in primary care: A clinical practice guideline from the American College of Physicians. Ann Intern Med 2005;142:525-531.)

General diet guidelines for achieving and maintaining a healthy weight include eating balanced, nutritious foods to avoid vitamin deficiencies. Avoiding foods high in fat and simple sugars should be emphasized. In addition, eating about 50% to 55% of calories from complex carbohydrates and educating patients regarding portion sizes and caloric content of foods is recommended by several national scientific organizations, such as the American Dietetics Association and American Diabetes Association. Referral to a registered dietitian helps patients initiate and adhere to these dietary guidelines.

Every physician should include an exercise regimen as part of a comprehensive lifestyle modification plan. Moderate exercise has been shown to decrease blood pressure, increase HDL and reduce triglyceride levels, and is predictive of maintenance of weight loss and delaying onset of type 2 diabetes.¹¹ General exercise recommendations include 20 to 30 minutes of moderate exercise 5 to 7 days a week, and up to 60 minutes a day most days of the week for maintenance of weight and 90 minutes a day for achieving weight loss.

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