Obesity

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Abstract

Editor's Note: This issue of In the Clinic has been updated. More than 30% of U.S. adults are obese (1). Generally defined as a body mass index (BMI) greater than 30 kg/m2, obesity is a serious chronic problem that is difficult to treat. Obesity is associated with increased all-cause mortality and increased risk for serious medical conditions, including type 2 diabetes, dyslipidemia, hypertension, and sleep apnea. People who are obese may also experience social stigmatization. Although weight loss is difficult to achieve and maintain, several approaches are available for losing weight. Even a loss of 5% body weight can substantially reduce the risks associated with obesity. Health Consequences What health problems are associated with being overweight? Excess body fat, particularly visceral fat, increases the risk for numerous diseases. The increased risk results from either the metabolic consequence of the enlarged fat cells or from the increased mass of fat (Table 1). Table 1. Obesity-Associated Health Problems The increased risk from the diseases associated with obesity substantially increases the risk for mortality. In essentially all studies, mortality and BMI have a J-shaped relationship. Among more than 90 000 women in the Women's Health Initiative, there was a graded increase in the risk for death as BMI increased from normal levels to greater than 40 kg/m2 (2). Another U.S. cohort of more than 80 000 men and women was monitored for more than 14.7 years with more than 1.23 million person-years of follow-up. Excluding deaths in the first 5 years, risk for death in patients younger than 55 years of age was directly related to BMI in both men and women, beginning at a BMI of 21 kg/m2 in women and 23 kg/m2 in men. In those older than 55 years of age, the increase in mortality occurred at a higher BMI, beginning at 25 kg/m2 in women and 30 kg/m2 in men (3). What is the evidence that weight loss improves health outcomes? There is good evidence that obese patients who lose weight reduce their risk for comorbid diseases, including diabetes, hypertension, sleep apnea, and cardiovascular disease, and experience improved overall quality of life. Even modest reductions in weight lead to improvement in health outcomes. Of 3234 study participants with impaired glucose tolerance randomly assigned to either intensive lifestyle modification (n = 1079), metformin (n = 1073), or placebo (n = 1062), those in the intensive lifestyle modification group experienced the best outcome, losing 7% or more of their body weight at 24 weeks, and 38% had a weight loss of 7% at average follow-up of 2.8 years. They had a 58% reduction in the risk for diabetes compared with patients in the placebo group (95% CI, 48% to 66%) (4). In the Framingham study, a modest weight loss of 6.8 kg or more led to a 28% reduction in the risk for hypertension among middle-age adults and a 37% reduction among older adults (5). In a clinical trial using lifestyle interventions to lower blood pressure (TOPH II), the risk for hypertension decreased by 65% in those who maintained their weight loss of 4.5 kg for 30 months (6). In a systematic review of long-term weight-loss studies in obese adults, both dietary and lifestyle approaches and pharmacologic interventions improved markers of cardiovascular disease, particularly in patients with cardiovascular risk factors at the beginning of the study (7). Clinical Bottom Line: Health Consequences Obesity increases the risk for numerous diseases, including type 2 diabetes, cardiovascular disease, pulmonary disease, and cancer. It also increases the risk for mortality, with risk increasing linearly with BMI. Even limited weight loss can substantially lower these risks. Screening and Prevention Should clinicians routinely screen patients for overweight or obesity? The U.S. Preventive Services Task Force recommends that clinicians screen all adult patients for obesity and offer intensive counseling and behavioral interventions to promote sustained weight loss for obese adults (8). The National Heart, Lung, and Blood Institute also recommends determining both height and weight in order to calculate BMI in all patients (see Box). Body Mass Index = kilograms of body weight divided by the square of the height in meters (kg/m2) The accepted definition of obesity is a BMI greater than 30 kg/m2, and overweight is defined as a BMI from 25.0 to 29.9 kg/m2 (9). Which health behaviors reduce the risk for becoming overweight? Certain health behaviors at different stages of life can reduce the risk for becoming overweight. Even during infancy and early childhood, risk factors for obesity may be present, and some of them are modifiable. Women can make certain efforts to lower the risk that their children will become overweight, including maintaining normal weight gain during pregnancy, not smoking, and extending duration of breast feeding (10, 11). Key factors predicting weight gain in children include high parental BMI, excessive weight gain in the first year, and a rise in BMI before ages 4 to 6 years (12). In addition to avoiding weight gain themselves, parents can encourage certain healthy habits in their children by making sure that they eat breakfast, limiting their intake of high sugar foods (including soft drinks and fruit drinks), reducing their time spent in such sedentary activities as watching television, and encouraging adequate sleep (13, 16). In people of all ages, monitored food intake and increased levels of activity, particularly walking and other forms of exercise, are associated with less future weight gain and should be encouraged (17). Some drugs are associated with weight gain (see Box), and clinicians may be able to substitute a medication that produces less weight gain to help patients avoid becoming overweight. Drugs that Produce Weight Gain Thioridazine Olanzepine Quetiapine Resperidone Clozapine Amitriptyline Nortriptyline Imipramine Mirtazapine Paroxetine Valproate Carbamazepine Gabapentin Insulin Sulfonylureas Thiazolidinediones Pizotifen Cyproheptadine Propranolol Terazosin Contraceptives Glucocorticoids Progestational steroids Clinical Bottom Line: Screening and Prevention Clinicians should measure BMI in all patients. Certain health behaviors, such as controlling caloric intake and engaging in regular physical activity, can reduce the risk for becoming overweight in adults and children. Some medications are associated with weight gain and should be avoided in patients at high risk for becoming overweight. Diagnosis How does one make the diagnosis of overweight and obesity? Clinicians should calculate the patient's BMI and follow it over time because BMI is easy to determine, very reliable, closely correlated with body fat, and linked with the broadest range of health outcomes (8, 18). The National Heart, Lung, and Blood Institute and the World Health Organization have adopted BMI as the criterion for defining overweight and obesity (9, 19). Both groups define a BMI of 18.5 to 24.9 kg/m2 as normal weight, a BMI of 25 to 29.9 kg/m2 as overweight, and a BMI greater than 30 kg/m2 as obesity. The Asia-Oceania Criteria differ slightly: Normal weight is 18.5 to 22.9 kg/m2, overweight is 23 to 24.9 kg/m2, and obesity is greater than 25 kg/m2 (20). At the same BMI, body fat is about 12% higher in women than in men (21). In what types of patients might BMI measurement be misleading? BMI may not be the best predictor of weight-related health problems in certain ethnic groups, such as African Americans and Hispanic-American women, who may have more fat-free mass in bone and muscle compared with Caucasians and thus misleadingly high BMI measurements. BMI may also be misleading in children, elderly patients, and athletes because of differences in height and proportions of fat and fat-free mass. In children, height-weight relationships are continually changing. During the first 5 to 7 years of life, BMI declines, reaches a nadir, and then begins to rise toward adult levels. BMI can be confusing in elderly individuals who have lost height, which makes the BMI seem higher than it really is. Because of decreased muscle mass in some older people, BMI may underestimate body fat. However, the effect of loss of height is more substantial. Similarly, athletes who have increased muscle mass and reduced fat mass may seem to have a high BMI but have little risk for obesity- associated diseases, such as cardiovascular disease or diabetes. When should clinicians measure waist circumference or waist-to-hip ratio in evaluating overweight and obese patients? Clinicians should consider measuring waist circumference and waist-to-hip ratio in most, if not all, overweight patients. Waist circumference may be a better measure of central adiposity, a correlate of visceral adiposity that is related to cardiovascular risk (although waist circumference does not improve prediction of cardiovascular risk in patients with a BMI of 35 or greater). Waist circumference is also a component of the metabolic syndrome as defined by the Adult Treatment Panel III of the National Cholesterol Education Program (22, 23). Table 2 shows criteria for the upper limits of normal waist circumference. Table 2. Criteria for Central Adiposity For individuals older than 75 years, the waist-to-hip ratio (waist circumference divided by hip circumference) may be a better predictor of death than either body mass index or waist circumference alone (24). Waist-to-hip ratios greater than 0.95 in men and 0.85 in women are considered elevated. Other measurements of fat mass, such as sagittal diameter and skin-fold thickness, can be made at the time of physical examination but are impractical in everyday clinical practice. What other factors and conditions should clinicians consider when evaluating overweight and obese patients? It is important to determine the patient's ethnicity and social situation; if the patient's parents were overweight; if there has been a recent l