22: Obesity

Obesity is one of the most common problems in clinical practice. Defined as a body mass index (BMI) of greater than 30 kg/m², over 33% of adult Americans are obese. An additional 35% are overweight, with BMIs between 25 and 30 kg/m². Almost one-third of children are overweight or obese. Because obesity is at the center of chronic disease risk and psychosocial disability for millions of Americans, its prevention and treatment offer unique patient care and public health opportunities. If all Americans were to achieve a normal body weight, it has been estimated that the prevalence of diabetes would decrease by half, whereas hypertension, coronary artery disease, and various cancers would decrease by 10–20%.

Obesity is often one of the most difficult and frustrating problems in primary care for both patients and physicians. Considerable effort is expended by primary care providers and patients, often with little benefit. Weight-loss diets, for example, even in the best treatment centers, result in an average 5–10% reduction in body weight. This lack of clinical success has created a never-ending demand for new weight-loss treatments. Approximately, half of women and one-quarter of men are “dieting” at any one time, spending billions of dollars each year on diet books, diet meals, weight-loss classes, diet drugs, exercise programs, “fat farms,” and other weight-loss aids. The challenge for health care providers is to identify those patients with obesity who are most likely to benefit medically from treatment and most likely to maintain weight loss, and to provide them with sound advice, skills for long-term lifestyle change, and support. For patients not motivated to attempt a weight-loss program, health providers must continue to be respectful and empathic and focus on other health concerns. Whenever possible, providers should emphasize prevention of obesity and further weight gain and the importance of physical fitness independent of body size.

Obesity is defined as an excess of body fat. Body fat can be measured by several methods including total body water, total body potassium, bioelectrical impedance, and dual-energy X-ray absorptiometry. In clinical practice, however, obesity is best defined by the BMI—body weight divided by height squared (kilograms per square meter). The BMI correlates closely with measures of body fat and with obesity-related disease outcomes. According to the National Institutes of Health (NIH), an individual with a BMI lesser than 18.5 kg/m² is classified as underweight, 18.5–24.9 kg/m² as normal, 25.0–29.9 kg/m² as overweight, and greater than or equal to 30.0 kg/m² as obese. Obesity is further classified as class I (BMI 30–34.9 kg/m²), class II (BMI 35–39.9 kg/m²), and class III or extreme obesity (BMI ≥40 kg/m²). The term “morbid obesity” is best avoided for those with class III obesity since obesity-related morbidity can occur at any obesity level.

Globally the prevalence of obesity doubled between 1980 and 2008. According to the World Health Organization, in 2008 10% of men and 14% of women in the world were overweight, compared with 5% for men and 8% for women in 1980. The prevalence of overweight and obesity were highest in the Americas and lowest in South East Asia. (though there is emerging evidence that the BMI cut-off point in Asian populations for overweight should be 22 kg/m2).

While overall the prevalence of obesity in the United States has increased dramatically over the last four decades in both adults and children differences between demographic groups are common. In women aged 40–59 years, for example, obesity is substantially more common in black and Hispanic women (52% and 47%, respectively) than in white women (36%). Similarly in teens, blacks and Hispanics (28% and 17.5%, respectively) have higher rates of obesity than whites (14.5%). Other subpopulations have dramatically increased rates of overweight and obesity. Eighty three percent of patients with mental illness, for example, are obese or overweight. Geographic differences in prevalence are also prominent in the United States. Obesity is more common in the southeastern United States than in other regions.

The relationship between body weight and mortality is curvilinear, similar to other cardiovascular risk factors. Most studies have demonstrated a J-shaped relationship, suggesting that the thinnest portion of the population also has an excess mortality. This is primarily due to the higher rate of cigarette smoking in the thinnest group except in the elderly, in whom malnutrition and being underweight is predictive of excess mortality independent of cigarette use. Recent analysis of the National Health and Nutrition Examination Study (NHANES) has suggested that overweight individuals may not have as much excess mortality as previously described and that the impact of obesity on mortality overall may be decreasing over time. Racial and ethnic factors may also impact the relationship of weight and mortality. In African Americans, the weight associated with the point of lowest mortality is greater than in whites, whereas in Asian Americans it is lower.

The increase in total mortality related to obesity results predominantly from coronary heart disease (CHD). Although it is not fully established that obesity is an “independent” risk factor for CHD, obesity is clearly an important risk factor for the development of many other CHD risk factors. Obese individuals aged 20–44 years, for example, have a three- to four-fold greater risk for type II diabetes, a five- to six-fold greater risk for hypertension, and twice the risk for hypercholesterolemia. The obese also have an increased risk for some cancers, including those of the colon, ovary, and breast.

As a result of these conditions, mortality from all causes for persons with class I obesity (BMI 30–34.9 kg/m²) is 20% greater than for those with a normal BMI. Individuals with class II obesity, BMI 35–39.9 kg/m², have an 80% increase in mortality from all causes. Mortality for extreme obesity, although less well studied, is estimated to be at least double that of normal weight individuals.

Obesity is also associated with a variety of other medical disorders, including degenerative joint disease of weightbearing joints, diseases of the digestive tract (gallbladder disease, gastroesophageal reflux disease), thromboembolic disorders, cerebrovascular disease, heart failure (both systolic and diastolic), respiratory impairment including sleep apnea, and skin disorders. Obese patients also have a greater incidence of surgical and obstetric complications, are more prone to accidents, and are at increased risk of social discrimination. Several studies have also shown a rate of depression higher in the obese than in normal weight subjects and a higher rate of binge eating disorder.

In addition to the total amount of excess body fat, the location of the excess body fat (regional fat distribution) is a major determinant of the degree of excess morbidity and mortality due to obesity. Increased upper body fat (abdomen and flank) is independently associated with increased cardiovascular and total mortality. Body fat distribution can be assessed by a number of techniques. Measurements of skin folds (subscapular and triceps) reflect subcutaneous fat. Measurement of circumferences (waist and hip) reflect both abdominal and visceral fat. Computed tomography (CT) and magnetic resonance imaging (MRI) scans measure subcutaneous and visceral fat. Clinically, measurement of the waist and hip circumference is most useful, especially in individuals with BMI 25–35 kg/m². A circumference in men greater than 102 cm (>40 in.) and in women greater than 88 cm (>35 in.) can be used to identify individuals at increased risk of developing obesity-related health problems.

Numerous lines of evidence, including both epidemiologic studies of adoptees and twins and animal studies, suggest strong genetic influences on the development of obesity. In a study of 800 Danish adoptees, for example, there was no relationship between the body weight of adoptees and their adopting parents but a close correlation with the body weights of their biological parents. In a study of approximately 4000 twins, a much closer correlation between body weights was found in monozygotic than in dizygotic twins. In this study, genetic factors accounted for approximately two-thirds of the variation in weights. Studies of twins reared apart and the response of twins to overfeeding showed similar results. Studies of regional fat distribution in twins have also shown a significant (but not complete) genetic influence.

Genetic studies have confirmed a clear relationship between genetics and obesity in both animals and humans. In humans, at least 24 genetic disorders, such as the Prader–Willi syndrome, are associated with obesity. Studies suggest that genetic influences may impact both energy intake (control of appetite and eating behavior) and energy expenditure.

Differences in the resting metabolic expenditure (RME), for example, could easily result in considerable differences in body weight as RME accounts for approximately 60–75% of total energy expenditure. The RME can vary by as much as 20% between individuals of the same age, sex, and body build; such differences could account for approximately 400 kcal of energy expenditure per day. Recent evidence suggests that the metabolic rate is similar in family members, and, as expected, individuals with lower metabolic rates are more likely to gain weight. Differences in the thermic effect of food, the amount of energy expended following a meal, may also contribute to obesity. Although some investigators have shown a decreased thermic effect of food in the obese, others have not.

Environmental factors are also clearly important in the development of obesity. The “built environment” refers to the impacts of urban sprawl, traffic congestion, and the associated sedentary lifestyle of the population as people spend more time in cars and in gridlock driving to work or shopping. The US Centers for Disease Control (CDC) estimates that urban sprawl due to lack of adequate land use planning is associated with increases in obesity, cardiovascular disease, and type 2 diabetes (see Chapter 9). Decreased physical activity and food choices that result in increased energy intake also clearly contribute to the development of obesity. Medical illness can also result in obesity, but such instances account for less than 1% of the cases. Hypothyroidism and Cushing syndrome are the most common. Diseases of the hypothalamus can also result in obesity, but these are rare. Major depression, which more typically results in weight loss, can also present with weight gain. Consideration of these causes is particularly important when evaluating unexplained, recent weight gain. Numerous medications can also result in weight gain including antipsychotics such as clozapine, olanzapine, and risperidone, antidepressants such as amitriptyline and cyproheptadine, anticonvulsants such as valproate, carbamazepine, and gabapentin, and diabetic medications such as insulin and thiazolidinediones. Of note, each of these categories of medications includes drugs that do not cause weight gain. Weight gain is also common following smoking cessation. On average, patients gain 4–5 kg within 6 months of quitting smoking but some patients may gain much more.

The BMI should be measured and recorded at each clinical encounter. As with other clinical abnormalities, patients should be nonjudgmentally informed of their BMI and how it conforms to definitions of overweight and obesity. Patients who are told that they are overweight or obese by their clinician are more likely to classify weight as a health concern and have greater desire and more attempts to lose weight.

Weight loss is indicated to assist in the management of obesity-related conditions, particularly hypertension, diabetes mellitus (type II) and prediabetes, hyperlipidemia, and metabolic syndrome in any patient who is obese (BMI >30 kg/m²). Many patients with BMI 25–30 kg/m² who have one of these conditions or significant psychosocial disability also often benefit from weight reduction.

Weight loss to prevent complications of obesity in patients without current medical, metabolic, or behavioral consequences of obesity is more controversial. In young and middle-aged individuals, particularly those with a family history of obesity-related disorders, treatment should be based on the degree of obesity and body fat distribution. Such individuals with upper body obesity (increased waist circumference) should be considered for treatment; those individuals with lower body obesity and no significant consequences of obesity can be reassured and monitored. Many such patients, however, desire weight loss for psychological, social, and cosmetic reasons. A careful discussion of the risks and benefits of weight loss in such instances helps patients make informed decisions about various weight-loss strategies.

A medical or psychosocial indication for weight loss is necessary but not sufficient to begin treatment. Treatment must be designed in the context of the patient’s readiness to change. The Transtheoretical Model of Change, also commonly known as the Stages of Change Model, is a useful framework for helping patients to modify their behavior. Developed and applied initially in smoking cessation, the model has also been used to modify eating and exercise behavior. It defines behavior change as a process of identifiable stages including precontemplation, contemplation, preparation, action, maintenance, and relapse. By understanding the patient’s stage of readiness to change, the clinician can work specifically with each patient to move him or her to the next stage (see Chapter 19).

Clinical assessment should also focus on how the current attempt compares with previous attempts; a realistic assessment of the patient’s goals for the amount and rate of weight loss; the extent to which outside stressors, mood disorders, or substance abuse might impair the attempt; and the degree to which others can provide support. Patient readiness to change can be further assessed by requiring the patient to complete specific pretreatment assignments. For example, patients can be asked to complete a 3-day diet record and to submit an exercise plan that includes both the type of aerobic exercise the patient plans to begin and how the patient plans to fit it into his or her schedule. When obesity coexists with other significant psychiatric disorders, particularly depression, binge eating disorder, and substance abuse, treatment should initially be directed at the concurrent disorder.

The goal of diet therapy for weight loss is to achieve a daily energy deficit whereby energy intake is less than energy expenditure. Daily energy expenditure can be estimated based on age, gender, and activity level. Two thousand calories (kcals) per day is often used as a reference level, but different individuals’ requirements may vary by hundreds of calories per day. The goal of most weight-loss diets is to achieve an energy deficit of approximately 500 kcal/day. Since a pound of fat equals approximately 3500 kcal, this will result in approximately 1 lb of weight loss per week.

Meta-analysis of randomized studies of dietary therapy to achieve weight loss have demonstrated an average weight loss of 5–10% of the starting weight in patients followed for 3 months to 1 year. Follow-up for up to 5 years suggests average long-term weight loss of 2–4% of initial weight. Of note, all studies have a substantial variation of response. Some patients, approximately 20%, are able to lose substantially more weight and keep it off for longer periods of time. Studies of commercial weight-loss programs also demonstrate modest amounts of weight loss but with wide variations. Weight Watchers, for example, reports 3.2% weight reduction at 2 years.

The optimal composition for weight-loss diets has been the subject of numerous clinical trials and, of course, thousands of popular weight-loss books. Most nutrition guidelines such as the Dietary Guidelines for Americans, recommend a low-fat, high-fiber, “balanced” diet. This approach emphasizes consumption of a wide variety of foods to achieve a balanced mix of macronutrients, that is, 20–35% of total calories from fats, 45–65% of total calories from carbohydrates, and 10–35% of total calories from protein. These ranges are substantially wider than earlier federal guidelines and allow for flexibility in diet design. The DASH (Dietary Approaches to Stop Hypertension) Eating Plan, originally developed for treatment of hypertension, is an example of a balanced diet that meets these macronutrient ranges and is supported by federal guidelines. A Mediterranean-style diet can also be used to achieve an energy deficit for weight loss and remain within these ranges.

Numerous clinical trials have compared this balanced approach with low carbohydrate diets such as the Atkins Diet and South Beach Diet. These studies have consistently shown equivalent amount of weight loss independent of the macronutrient composition of the diet. Rather than nutrient composition, weight loss was predicted by adherence to the diet. Satiety, hunger, lipid levels, insulin levels, and other metabolic factors were also found to be equivalent despite large differences in macronutrient composition. Similar findings have been published with comparisons of the very low-fat Ornish diet, the Zone diet, and other diets with various combinations of macronutrients. Thus, patients can be reassured that almost any whole food diet can result in safe weight loss as long as the patient consistently follows the diet.

An important alternative in the dietary treatment of obesity is the use of safe and effective very low-calorie diets (VLCDs). Previously known as protein-sparing modified fasts and protein-formula liquid diets, these diets restrict calorie intake to less than or equal to 800 kcal/day. Patients ingest only prepackaged, often liquid, food that provides adequate protein, vitamins, and minerals. Additional intake is limited to 2–3 quarts of calorie-free beverages per day. The major advantage of these diets is the “complete removal of patients from the food environment” to facilitate short-term adherence. In addition, the significant energy deficit results in rapid weight loss, usually 2 lb/week, encouraging the patient to continue. Ongoing concerns about these diets include their cost, side effects, and long-term results. Clinical trials suggest that the use of 800-kcal VLCDs can lower cost and prevent most of the significant side effects associated with the lower-calorie (400–600) VLCDs, including gallstones and fluid and electrolyte disorders, with equal long-term efficacy.

As with standard diet therapy of obesity, VLCDs require adherence during the diet, and long-term nutritional and behavioral changes to maintain weight loss. Well-planned programs that combine VLCDs with nutrition education, behavior therapy, exercise, and social support report improved long-term results. For example, an average weight loss of 55 lb with 75% and 52% of the loss maintained at 1- and 2 1/2-year follow-up, respectively, and maintenance of an average of 24 lb after 2- to 3-year follow-up have been reported. Meta-analysis of published VLCD trials suggest that while initial weight loss is greater with VLCDs than standard diets, both approaches have equal long-term results. As with other approaches, however, there is a wide variation of response with VLCDs, and some patients can achieve long-term weight loss. Because of the quicker and greater amounts of weight loss, VLCDs may be particularly useful in situations in which rapid weight loss is clinically indicated such as preoperative treatment (joint replacement, transplant surgery, bariatric surgery) or for initial management of severe medical conditions (severe sleep apnea, poorly controlled diabetes, heart failure, or coronary artery disease).

Recent studies have helped elucidate predictors of long-term weight maintenance after diet therapy for weight loss. Most important has been information from the National Weight Control Registry. This cohort of individuals who have lost an average of 33 kg and maintained the loss for 5 years report consumption of low-calorie, low-fat diets averaging approximately 1400 cal/day; high levels of physical activity averaging 60 minutes/day; regular self-monitoring of body weight; eating breakfast daily; and maintaining consistent dietary patterns on weekdays and weekends.

Surprisingly, few studies have examined the effects of weight loss on morbidity and mortality. Studies examining the effect of weight loss on cardiovascular risk factors generally show beneficial changes with weight loss as predicted. Descriptive studies on mortality, however, show inconsistent results. Such descriptive studies are unable to clarify if changes in mortality are caused by the weight change, if disease or other factors that contribute to disease, such as cigarette smoking, cause weight loss, or if both are related to a third factor. No randomized trials of long-term effects of voluntary weight loss on mortality have been published.

Because so many Americans are dieting at any one time, and having so little long-term success, considerable interest has focused on the potential adverse effects of weight cycling (“yo-yo” dieting). Numerous adverse effects of weight cycling have been hypothesized, primarily from animal studies. These include making further weight loss more difficult, increasing total body fat and central obesity, increasing subsequent calorie intake, increasing food efficiency, decreasing energy expenditure, increasing levels of adipose tissue lipolytic enzymes and liver lipogenic enzymes, increasing insulin resistance, increasing blood pressure, and increasing blood cholesterol and triglyceride levels. Most experts currently feel that these phenomena occur inconsistently, if at all. Descriptive studies that have addressed this question by looking at the impact of weight fluctuations on CHD incidence, CHD mortality, and total mortality have shown mixed results.

There is also debate over whether weight-loss diets cause eating disorders or binge eating. Although a history of dieting often precedes the development of eating disorders, there is no evidence proving a causal link. In addition, approximately 50% of individuals with binge eating disorder report that binging preceded dieting. There is also some evidence to suggest that successful weight loss may reduce binge eating in the obese (see Chapter 23).

Thus, there is only indirect evidence suggesting that dieting has negative health effects. This remains an important question, however, and reinforces the idea that casual attempts at quick weight loss should be avoided. At present, however, committed attempts at long-term weight loss should not be discouraged because of adverse health effects or the potential of regaining weight.

Dieting also has a significant effect on energy balance both during and after weight loss. As every successful dieter has observed, the rate of weight loss slows during the course of dieting. Because this can be quite discouraging to the unwary patient (or uninformed health care provider), it is important to inform the patient prior to initiating a weight-loss diet that this is likely to occur. Weight loss is most rapid during the initial days of hypocaloric feeding due to changes in sodium and water balance caused by early loss of glycogen and protein (both contain water) and, depending on the degree of calorie deficit and type of diet, loss of sodium associated with ketonuria. Following this initial phase, weight loss depends on the extent of energy deficit. With time, however, the rate of weight loss slows again as the body’s metabolic rate decreases and the energy deficit becomes smaller. This change in metabolic rate can be two to three times greater than that predicted from changes in body weight. The lower the energy content of the diet, the lower the metabolic rate. Although it was initially suggested that exercise occurring during a period of hypocaloric feeding could prevent this decrease in metabolic rate, recent studies have suggested that it has no direct effect during hypocaloric feeding (but exercise may increase the postdiet metabolic rate by preserving lean body mass).

Following the period of hypocaloric feeding (resumption of normal energy intakes), the resting metabolic rate increases, but to a level below that observed before beginning the diet. This reduction is in part a reflection of the loss of lean body mass and in part due to additional, poorly understood effects on energy metabolism. Overall energy expenditure is further reduced due to a decrease in the thermic effect of food (the individual eats less) and in differences in physical activity (it takes less energy to perform the same amount of activity for a smaller person). Thus, to maintain weight loss, individuals need to consume less energy than before dieting and increase energy expenditure by increasing the amount of physical activity.

Exercise offers a number of significant advantages to patients attempting to achieve long-term weight loss. First and foremost, exercise increases energy expenditure, helping to create the energy deficit necessary for weight loss. Unfortunately, the amount of energy expended during most aerobic exercises (e.g., walking, jogging, and swimming) for the typical periods performed (30 minutes four to five times per week) is modest, approximately 1000–1500 kcal/week. Thus, exercise can be predicted to have little effect on short-term weight loss. Clinical trials reflect this modest effect: some studies demonstrate weight loss with exercise alone or extra weight loss when exercise plus diet is compared with diet alone, but other studies do not show such an effect. In a meta-analysis of 43 studies, exercise combined with diet lead to 1.1 kg greater weight loss than diet alone. Studies comparing high-intensity exercise to low-intensity exercise demonstrated a 1.5 kg greater weight loss.

The importance of exercise for successful maintenance of weight loss is more clearly established. As discussed above, an hour per day of exercise was one of the predictors of long-term weight maintenance in the National Weight Control Registry. In addition to the cumulative effect of increased energy expenditure, exercise affects the composition of the body substance lost during weight loss. When exercise is directly compared with diet, or when exercise plus diet is compared with diet alone, exercise results in greater preservation of lean body mass. That is, for each pound of weight lost, less fat and more muscle are lost during weight-loss programs without exercise. This is particularly important as the body’s RME (a major portion of the total daily energy expenditure) is closely correlated with lean body mass.

The observation that much of the long-term effect of exercise is through preservation of lean body mass has resulted in an increased interest in the potential role of resistance training (e.g., weight lifting, and circuit training). Preliminary results suggest that resistance training during dieting does result in maintenance of lean body mass compared with the result from dieting alone. Thus, highly motivated patients can be instructed to add resistance training to their aerobic exercise program.

Regular aerobic exercise results in a number of other benefits to the obese patient, including improved cardiovascular training effect (increased exercise tolerance), decreased appetite (per calorie expended), a general sense of well-being, decreased blood pressure (in hypertensives), improved glucose metabolism and insulin action (in diabetics), improved blood lipids (in lipid disorders), and, in the long term, decreased mortality from cardiovascular disease and all other causes.

Young patients with mild-to-moderate obesity can be started directly on a regular aerobic exercise program. Patients are commonly instructed to select two exercises and to perform either one of them six times per week for 30–60 minutes/day. Patients are taught to take their pulse and to generate a sustained tachycardia at 70–80% of their maximum predicted heart rate. Sedentary patients, older patients, and patients with severe obesity are instructed to begin walking programs without initial concern about meeting target heart rates. In these patients, the focus is on frequency and duration, rather than intensity. As weight loss proceeds and patients become used to exercising regularly, they can be advanced to formal aerobic programs.

Sustained weight loss requires long-term changes in eating and exercise behavior. Patients must learn specific skills to facilitate decreased calorie intake and increased energy expenditure. Behavior therapy, combined with diet and exercise, forms the core of the most standard “lifestyle modification” approaches to weight management. Behavior therapy can be implemented in groups or in individual therapy. Trained psychologists and dieticians commonly lead such efforts, but office-based clinicians can often learn to use many of the same techniques. Intensity of interaction appears to be one of the predictors of success. In the highly successful Diabetes Prevention Project, for example, lifestyle modification was taught in 16 individual sessions over 24 weeks.

Meta-analysis of 36 studies of behavior therapy for weight loss showed that behavior therapy alone resulted in significantly greater weight loss, a decrease of 2.5 kg, than placebo. When behavior therapy was combined with diet and exercise and compared to diet and exercise alone, the combined treatment also resulted in greater weight loss in five of six studies. Two studies compared cognitive behavioral therapy (CBT) plus diet and exercise with diet and exercise alone. In these studies, the combined treatment lost 4.9 kg more.

Standard behavior therapy relies on specific techniques to teach the skills needed to change problematic behaviors.

1. Goal-setting: Patients are taught to set specific quantifiable, realistic goals at the outset of behavior therapy and during each week of therapy. Succeeding at meeting realistic goals creates a sense of self-efficacy and can reinforce further change.

2. Self-monitoring: Patients are taught to monitor both food and beverage intake and physical activity. Specific attention must be directed at teaching patients how to estimate portion sizes since patients may underestimate intake by 50%. The context, degree of hunger, and emotional state of each time of eating is also recorded. This may allow eating-related factors to be targets for modification. Patients are also instructed to record all programmed physical activity. Additional monitoring of physical activity can be done with pedometers.

3. Stimulus control: Patients are instructed to identify stimuli that increase the likelihood of both desired and undesired behaviors. Particular emphasis is placed on attempting to modify nonfood cues that are associated with eating. Similarly, simple techniques such as keeping certain problem food out of the house may be useful.

4. Cognitive skills: Patients are taught skills for problem solving and cognitive restructuring. Patients are asked to identify problems, consider potential solutions, list the advantages and disadvantages of each, select a feasible solution, and evaluate the results. Cognitive restructuring involves identification of dysfunctional thoughts that interfere with goals and replacing such thoughts with more rational ones. Formal CBT can also be used as part of weight management. Cognitive behavioral therapy places more emphasis on cognitive change, rather than behavioral change, as the primary focus of treatment.

Social support is an additional essential component for any successful weight-loss program. Most successful programs use peer group support. Diet partnerships and financial incentives are effective for some patients. Involvement of family members is also important. A comprehensive review of published results of weight-loss programs strongly suggests that close provider–patient contact is a better predictor of success than the particular weight-loss intervention.

Medications for the treatment of obesity are widely available over the counter, via the Internet, and by physician prescription. A CDC survey suggested that 7% of Americans used nonprescription weight-loss drugs. Among young obese women and among those on prescription weight-loss medications the use of nonprescription weight-loss medications was 28.4% and 33.8%, respectively.

A variety of weight-loss medications are available by prescription in the United States. These include various amphetamines (Drug Enforcement Administration schedule II), benzphetamine and phendimetrazine (schedule III), and phentermine, diethylpropion, mazindol, and orlistat. Most obesity experts agree that there is no current role for the schedule II or III drugs. Orlistat, at half the prescription dose, is available for over-the-counter use in the United States. Two additional medications, lorcaserin and the combination of phentermine and topiramate were approved by the Food and Drug Administration (FDA) in 2012. Sibutramine was withdrawn from the market in the United States in 2010 due to a large randomized controlled study that showed a 16% increase in cardiovascular events in patients in the medication group.

Lorcaserin is a selective serotonin receptor agonist. In one randomized, year-long study of over 3000 adults, the medication resulted in an additional loss of initial weight of approximately 3.5% compared with placebo. Common adverse events include headache, dizziness, and nausea. Other concerns include attention and memory disturbances, depression, priapism, and serotonin syndrome. No increase in valvulopathy (as seen previously with other serotonin receptor agonists) has been reported. The medication is contraindicated in pregnancy.

A combination medication consisting of phentermine and topiramate, is also approved by the FDA for weight loss. A study of over 4000 subjects showed a 8.9% greater loss of initial weight than in patients on placebo. However, concerns persist about the increased heart rate seen in the group on medication and an increased incidence of cleft lip. Other side effects include mood disorders, increased suicidal thoughts, insomnia, impaired concentration, other cognitive dysfunction, paresthesia, dizziness, dysgeusia, constipation, and dry mouth. This medication is also contraindicated in pregnancy and is only available in certified pharmacies to facilitate careful postmarket monitoring.

Considerable controversy exists about the efficacy of and indications for these medications. Numerous clinical trials, some up to 2 years in duration, demonstrate statistically significant weight loss in subjects who take an obesity medication compared with placebo. Total loss of initial weight is modest, averaging about 5% greater than placebo. There is no convincing evidence that any one of these medications results in more weight loss than others. Although some studies also show improvement in obesity-related metabolic abnormalities (e.g., blood sugar, blood pressure, and lipids), these reductions are also small and are substantially less than those achieved with hypoglycemic, antihypertensive, or lipid-lowering medications. In addition, no studies have yet demonstrated that weight loss achieved with medications results in reductions in obesity-related mortality or cardiovascular disease outcomes.

The NIH guidelines state that the FDA-approved weight-loss drugs may be useful as an adjunct to diet and physical activity for patients with BMI greater than or equal to 27 kg/m² and obesity-related risk factors or diseases, and for any patient with BMI greater than or equal to 30 kg/m². Based on the modest efficacy noted above, however, these guidelines have not been widely implemented by clinicians. Prescriptions for weight-loss drugs should be limited to patients adhering to weight-loss diets and physical activity. In addition, weight loss in the first month of use correlates highly with weight loss at 12 months. Thus, for patients in whom no weight loss is achieved within the first month of use, weight-loss medications should be discontinued.

Surgery for weight loss is typically considered the last resort for patients with severe obesity. The NIH guidelines state that weight-loss surgery may be an option for carefully selected patients with BMI greater than or equal to 40 or greater than or equal to 35 kg/m² with comorbid conditions. Such patients must be at high risk for obesity-related morbidity and mortality, must have failed medical therapy, must have stable psychiatric status, and must be fully committed to lifetime lifestyle changes.

In recent years, the use of surgery to treat obesity has grown substantially. With implementation of new techniques and the use of less invasive approaches, obesity surgery is now one of the fastest growing operations in the United States. A majority of procedures are now done laparoscopically and some are being done as an outpatient procedure.

Available surgical procedures include: malabsorptive procedures such as duodenal switch and biliopancreatic diversion; restrictive procedures such as vertical banded gastroplasty, adjustable gastric band, and sleeve gastrectomy; and combined procedures such as roux-en-Y gastric bypass. Most centers have avoided malabsorptive procedures, despite excellent weight loss, due to concerns of potential metabolic and nutritional sequelae analogous to those observed with jejuno-ileal bypass procedures in the past. Restrictive procedures, particularly the laparoscopic adjustable gastric band are gaining in popularity. Advantages include reduced perioperative morbidity and mortality compared to other procedures. Weight loss is less than other procedures, however, and intermediate and long-term complications are greater. Complications include prolapse of the stomach through the band, infected reservoir sites, heartburn and regurgitation, and severe esophagitis. Approximately one-third of banding procedures require conversion to a roux-en-Y bypass.

The roux-en-Y bypass is the most common bariatric procedure in the United States. Weight loss, approximately one-third of initial weight, is greater than with purely restrictive procedures. Serious perioperative complications are greater, however, and include bleeding and gastrojejunostomy leaks. Perioperative mortality occurs in 0.3% of cases, even in the best centers, and has been shown to be substantially higher in open procedures (compared to laparoscopic procedures), in patients with a history of thromboembolic disease, sleep apnea, and impaired functional status, and in older and sicker patients. Approximately 4% of patients will have early complications including deep venous thrombosis, surgical reintervention, or spend greater than 30 days in the hospital. Intentional weight loss of 5–10% of initial weight before weight loss surgery is associated with reduced perioperative complications.

Longer term complications include nutritional deficiencies of fat-soluble vitamins, especially vitamin D, iron, B₁₂, folate, and calcium. Weight regain over time is also commonly observed. In one study, weight loss at 10 years decreased from 38% at year 1 to 25% at year 10.

Beneficial effects of weight loss surgery include marked improvement in diabetes, hyperlipidemia, hypertension, sleep apnea, and other obesity-related symptoms. Overall mortality over 11 years is improved by 24%, but the number needed to treat to prevent one death per year is approximately 850 patients.

Due to the high prevalence of obesity and obesity-related morbidity, and the increasing use of operative procedures to treat obesity, such patients are increasingly cared for in inpatient and critical care settings. In most respects, care is similar to that of nonobese patients; however, severely obese patients require special attention in several aspects of care. Technical procedures may be more difficult in the obese patient including intubation, tracheostomy, and vascular access. Blood pressure monitoring requires use of cuffs with bladders large enough to cover 80% of the arm circumference. Undersized cuffs can overestimate blood pressure significantly. Dosing of some medications must be adjusted in obese patients due to the larger volume of distribution for lipophilic drugs. Some drugs should be dosed according to the ideal body weight, others according to the actual weight, and some according to an intermediate weight. Similar issues are encountered with nutrition support in the obese patient. Use of the actual body weight in common energy estimation equations such as the Harris–Benedict equation is likely to overestimate energy requirements. If indirect calorimetry is not available to measure energy expenditure, the use of the ideal body weight, or an intermediate dosing weight, is less likely to result in complications of overfeeding.

Obesity and obesity-related illnesses are a major public health crisis. Currently available treatments with diets, exercise, and behavior therapy provide limited efficacy for most patients. Some patients, however, can achieve long-term weight loss. Currently approved medications demonstrate limited efficacy. Surgical treatment of obesity is the most effective treatment but is associated with substantial risk and long-term complications. Given the lack of effective therapy, preventive measures are essential. Broad and ambitious public health approaches are required to impact the obesity epidemic. For most individual patients, dietary changes that emphasize calorie reduction by consuming smaller portions, more plant foods, fewer high-calorie beverages, and less fast food are necessary even to maintain current weight. Similarly, striking increases in daily physical activity are needed to maintain body weight and achieve fitness.