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According to reports from the CDC, national obesity rates continue to rise, with only one state maintaining an obesity rate below 20%. Statistics indicate that 32.2% of men and 35.5% of women in the United States are obese. Non-Hispanic black women and Mexican-American women experience a greater prevalence of obesity than their white counterparts.1 In 2010, researchers found diminishing life expectancies related to BMI >35 by as many as 12 years.2 Furthermore, the overall obesity prevalence in children and adolescents is 16.3%;3 nearly 20% of our 4-year-old population is already obese.4 This worsening trend, however, is not limited to the United States. While obesity rates in high-income nations continue to climb, they are now also rising dramatically in low-to-middle-income nations, with 1.6 billion adults thought to be overweight or obese worldwide.5
Healthy People 2010 goals of reducing the prevalence of overweight and obesity to less than 15% were admittedly lofty when established in 2000. This goal was set when the United States was experiencing rising obesity rates, with more than 50% of states seeing rates in excess of 20%. Between 1988 and 2008, there was a 69% increase among individuals aged 20 to 30 years. In recognition of this, Healthy People 20206 strives to achieve a 10% reduction in obesity.
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Etiology
The etiology of obesity is multifaceted. The condition results from an energy imbalance between calories consumed vs. calories expended. Western diets have become heavy in energy-dense foods, including fats, sugars, and high-starch components, much of which reflects our growing taste for fast food and reliance on prepackaged foods. Since the mid-20th century, portion sizes have doubled from 6-oz sodas with 325 kcal hamburgers to 20-oz sodas with 590 kcal burgers. Americans scarf down food, failing to allow signals of satiety to reach the brain, and snack more frequently on such non-nutritional products as candy and soft drinks.
Additionally, an increasingly automated society leads to decreased physical activity, which diminishes our caloric expenditure. Rather than playing outside, children now entertain themselves by playing video games, surfing the Internet, and sending text messages.
Other factors contributing to obesity include poor lifestyle habits and choices, influence of social networks, conceptualizations of food, and various health-related issues. Beginning in the late 1990s, studies began to reveal a correlation between inadequate sleep and obesity.7 Growing evidence supports the belief that hormonal imbalances form the basis of that relationship.8 A study found that women with consistent poor sleep quality generally put on more weight than those who slept well.9 The Framingham Offspring Study found that obese people tend to associate with other obese people, hindering their recognition of abnormal weight gain.10
Impact of obesity on body systems
As the percentage of adipose tissue in the body increases, the cardiopulmonary systems experience a greater workload. Physiologically, the body requires more circulating blood for the excess adipose tissue, which leads to increased pre-load, stroke volume, cardiac output, and myocardial workload. Ventricular hypertrophy is common, as is diastolic dysfunction; the latter leads to poor fluid tolerance. The greater requirement for RBCs leads to greater blood viscosity. The pulmonary system struggles with the increased intra-abdominal pressure and elevated diaphragm, which reduces the functional residual capacity. The increase in pulmonary blood volume and carbon dioxide makes breathing more difficult. This causes hypoventilation and atelectasis, resulting in a ventilator-perfusion mismatch. Up to 70% of the obese population has undiagnosed obstructive sleep apnea (OSA).
Metabolic syndrome, hyperinsulinemia, and diabetes mellitus are all on the rise due to poor dietary intake and lack of routine exercise. Irritable bowel syndrome, fatty liver, and gastroesophageal reflux disease are common manifestations within the obese population. Hormonal imbalances of ghrelin and leptin have been shown to occur with sleep deprivation.11 Low levels of leptin trigger cravings for carbohydrate-rich foods, and high levels of ghrelin trigger hunger. Emerging research indicates that abnormal leptin levels impair renal and cardiac function.12
Obesity contributes to many other health problems as well (Table 1). It has been found to be a risk factor for numerous cancers and is problematic in facilitating an early diagnosis.13 Higher levels of neuropeptides are thought to be a cause of the chronic migraines associated with obesity.14 Growing evidence links obesity and metabolic disorders with the development and progression of cognitive problems.15 Additionally, eating disorders and depression are often associated with obesity.
The back and lower extremities bear the brunt of the excess body weight and contribute to joint pain that in turn hinders mobility, initiating a negative spiral of worsening pain, disuse atrophy of the musculature, and worsening weight gain. A recent study revealed a link connecting obesity, inactivity, and the development of fibromyalgia. Based on health surveys of 16,000 women, researchers found inactive, obese females were 60% to 70% more likely to develop fibromyalgia.16
Identifying obesity
BMI is currently considered the standard by which most health-care professionals determine degree of obesity (Table 2). While this is an accurate reflection of excess body fat, BMI calculations still fall short. Because of the dramatic growth and developmental changes occurring in the first 20 years of life, the pediatric population is misrepresented if age and gender are not calculated into the equation. Ethnic background may also generate false results, as indicated by the tendency for black individuals to have lower body-fat ratios. Higher abdominal circumference is more often associated with greater incidence of comorbidity. In fact, the Mayo Clinic developed the term “normal-weight obesity” after recognizing the higher risk of metabolic problems in those individuals with a normal BMI but high body-fat content.
The most accurate method for determining body fat is dual-energy x-ray absorptiometry, which unfortunately is not readily available in most medical practices. Calculating the patient’s waist-to-height ratio helps to risk-stratify for comorbidities when used in conjunction with BMI. For the pediatric population, researchers at the University of Michigan’s Mott Children’s Hospital found measurements of neck circumference to be a reliable technique for assessing whether children are overweight or obese.
