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Obesity is now a true epidemic and public health crisis that both clinicians and patients must face. Normal body weight is defined as a body mass index (BMI), calculated as the weight in kilograms divided by the height in meters squared, of less than 25; overweight is defined as a BMI = 25.0–29.9, and obesity as a BMI greater than 30. Between 1980 and 2013, there was an 8% increase worldwide in the proportion of men and women with a BMI greater than 25. The most recent national data reveal that one-third of adults in the United States are obese, and prevalence rates are higher in blacks and Hispanics compared to non-Hispanic whites. This trend has been linked both to declines in physical activity and to increased caloric intake.

Risk assessment of the overweight and obese patient begins with determination of BMI, waist circumference for those with a BMI of 35 or less, presence of comorbid conditions, and a fasting blood glucose and lipid panel. Obesity is clearly associated with type 2 diabetes mellitus, hypertension, hyperlipidemia, cancer, osteoarthritis, cardiovascular disease, obstructive sleep apnea, and asthma. In addition, almost one-quarter of the US population currently has the metabolic syndrome.

Metabolic syndrome is defined as the presence of any three of the following: waist measurement of 40 inches or more for men and 35 inches or more for women, triglyceride levels of 150 mg/dL (1.70 mmol/L) or above, HDL cholesterol level less than 40 mg/dL (less than 1.44 mmol/L) for men and less than 50 mg/dL (less than 1.80 mmol/L) for women, blood pressure of 130/85 mm Hg or above, and fasting blood glucose levels of 100 mg/dL (5.55 mmol/L) or above. The relationship between overweight and obesity and diabetes, hypertension, and coronary artery disease is thought to be due to insulin resistance and compensatory hyperinsulinemia.

Obesity is associated with a higher all-cause mortality rate. Data suggest an increase among those with grades 2 and 3 obesity (BMI more than 35); however, the impact on all-cause mortality among overweight (BMI 25–30) and grade 1 obesity (BMI 30–35) is questionable. Persons with a BMI of 40 or higher have death rates from cancers that are 52% higher for men and 62% higher for women than the rates in men and women of normal weight. Significant trends of increasing risk of death with higher BMIs are observed for cancers of the stomach and prostate in men and for cancers of the breast, uterus, cervix, and ovary in women, and for cancers of the esophagus, colon and rectum, liver, gallbladder, pancreas, and kidney, non-Hodgkin lymphoma, and plasma cell myeloma (previously called multiple myeloma) in both men and women.

In the Framingham Heart Study, overweight and obesity were associated with large decreases in life expectancy. For example, 40-year-old female nonsmokers lost 3.3 years and 40-year-old male nonsmokers lost 3.1 years of life expectancy because of overweight, and 7.1 years and 5.8 ...

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