Porth's Essentials of Pathophysiology, 4e

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Integrative Body Functions

U N I T 2

Overweight and Obesity Overweight and obesity have become global health prob- lems, increasing the risk of hypertension, hyperlipidemia, type 2 diabetes, coronary heart disease, and other health problems. According to recent worldwide estimates, 1.7 billion people are classified as overweight, more than 1 billion have hypertension, and more than 500 million have either diabetes or impaired glucose tolerance. 17 Obesity is defined as having excess body fat, enlarged fat cells, and even an increased number of fat cells. 18 Clinically, obesity and overweight have been defined in terms of the BMI. Historically, various world bodies have used different BMI cutoff points to define obesity. In 1997, the World Health Organization (WHO) defined the vari- ous classifications of overweight (BMI ≥ 25) and obesity (BMI ≥ 30). This classification was subsequently adopted by the National Institutes of Health (NIH). 13 The use of a BMI cutoff of 25 as a measure of overweight raised some concern in that the BMI of some men might be increased due to muscle rather than fat weight. However, it has been shown that a BMI cutoff of 25 can sensitively detect most overweight people and does not erroneously detect overly lean people. An important caveat is that cer- tain ethnicities (e.g., Asians), can develop complications from lower levels of BMI and waist circumference than Caucasians. This has resulted in ethnicity-specific defini- tions being adopted (e.g., overweight in Asians is defined as >23) by the WHO. Obesity is associated with increased risk for develop- ing many medical, psychosocial, and behavioral prob- lems. In terms of health problems, many disorders occur more frequently in obese people (Fig. 10-2). The most important and common of these are hyperlipidemia, hypertension, coronary artery disease, stroke, and type 2 diabetes mellitus. The increased weight associated with obesity stresses the bones and joints, increasing the likelihood of osteoarthritis. Certain cancers (endome- trial, prostate, colon, uterine, ovarian), thromboembolic disorders, and gastrointestinal tract disease (gastro- esophageal reflux and gallbladder disease) are also more prevalent in the obese. 19 Other conditions associatedwith obesity include sleep apnea and pulmonary dysfunction, menstrual irregularities and complications of pregnancy, psychological distress, and nonalcoholic fatty liver dis- ease (discussed in Chapter 30). Because some drugs are lipophilic and exhibit increased distribution in fat tissue, the administration of these drugs, including some anes- thetic agents, can be more dangerous in obese persons. If surgery is required, obese persons heal slower and are at increased risk from anesthesia. Massive obesity, because of its close association with so many health problems, can be regarded as a disease in its own right. It is the second leading cause of preventable death. Causes of Overweight and Obesity Factors that are thought to lead to the development of overweight and obesity include the interaction of gen- otype and environmental factors, including diet and

Cerebral atherosclerosis, stroke

Hypertension, left ventricular hypertrophy

Sleep apnea

Coronary artery atherosclerosis, myocardial infarction

Fatty liver Gallstones

Diabetes

Osteoarthritis

Risk of endometrial cancer Hyperlipoproteinemia

Polycystic ovaries (younger women)

FIGURE 10-2. Clinical manifestations of obesity.

physical activity. Obesity is known to run in families, suggesting a hereditary component. The question that surrounds this observation is whether the disorder arises because of genetic endowment or environmen- tal influences. Studies of twin and adopted children have provided evidence that heredity contributes to the disorder. 20 The most recent update of the human obesity gene map suggests that there are about 30 obe- sity candidate genes that might contribute to the risk of obesity in humans. 21 It is unknown what combina- tions of genes and mutations are involved in these risk factors and how environmental factors interact with them. Although genetic factors may explain some of the individual variations in terms of excess weight, environ- mental influences are major contributors. These influ- ences include family eating patterns, inactivity because of labor-saving devices and time spent on the computer and watching television, reliance on the automobile for transportation, easy access to food, energy density of food, increased consumption of sugar-sweetened bev- erages (especially fructose), 22 and increasing portion sizes. 23 The obese may be greatly influenced by the avail- ability of food, the flavor of food, time of day, and other cues. The composition of the diet also may be a causal