Porth's Essentials of Pathophysiology, 4e

232

Integrative Body Functions

U N I T 2

The presence of excess fat in the abdomen out of pro- portion to total body fat is an independent predictor of risk factors and mortality. Both BMI and waist circum- ference are positively correlated with total body adipose tissue, but waist circumference is a better predictor of abdominal or visceral fat content than BMI. 28 A waist circumference of 88 cm (35 inches) or greater in women and 102 cm (40 inches) or greater in men has been asso- ciated with increased health risk 13 (see Table 10-2). In general, men have more intra-abdominal fat and women more subcutaneous fat. As men age, the proportion of intra-abdominal fat to subcutaneous fat increases. After menopause, women tend to acquire more intra-abdom- inal fat. Increasing weight gain, alcohol, and low levels of activity are associated with central obesity. Although central obesity is usually considered to be synonymous with visceral fat, CT or MRI scans can differentiate central obesity into visceral fat and subcu- taneous fat. Visceral fat stores are believed to be more lipolytically active than subcutaneous fat and have a greater potential to affect liver metabolism, given the fact that the fatty acids in their venous drainage flow directly to the liver. In addition to their lipolytic effects, visceral adipocytes produce greater amounts of adipocytokines (e.g., TNF- α , IL-6), except adiponectin whose levels are decreased, resulting in a more insulin resistant, proin- flammatory, and proatherosclerotic environment. These changes contribute to the development of systemic insu- lin resistance, hypertension, hyperlipidemia, and other features of the metabolic syndrome, and are thought to be associated with greater cardiometabolic risk. 15 Cardiometabolic risk represents the overall risk of developing diabetes and/or atherosclerotic cardiovascu- lar disease (e.g., myocardial infarction, stroke) due to a cluster of modifiable risk factors. These include abdomi- nal obesity, dyslipidemia (elevated levels of triglycerides and low-density lipoproteins and decreased levels of high-density lipoproteins), hypertension, insulin resis- tance and elevated blood glucose levels, the presence of inflammatory cytokines, and smoking. Emerging risk factors include endothelial dysfunction and a prothrom- botic state. Many of these risk factors are also key com- ponents of what is termed the metabolic syndrome (see Chapter 33). 15,16 Visceral obesity is also associated with many other conditions including cancer (e.g., breast and endometrial cancer), gallbladder disease, osteoarthritis, menstrual irregularities, and infertility (especially as part of the polycystic ovarian syndrome) (see Fig. 10-2). Weight loss causes a preferential loss of visceral fat (due to higher turnover of visceral fat cells than subcutaneous) and can result in improvements inmetabolic and hormonal abnormalities. Although peripheral obesity is associated with varicose veins in the legs and mechanical problems, it is not as strongly associated with cardiometabolic risk. Prevention andTreatment of Obesity Emphasis is being placed on the prevention of obesity. It has been theorized that obesity is preventable because the effect of hereditary factors is no more than moderate.

A more active lifestyle together with a low-fat diet (<30% of calories) is seen as the strategy for prevention. The target audience should be children, adolescents, and young adults. 29 Tools needed to achieve this goal include promotion of regular meals, increased intake of fruits and vegetables, substituting water for calorie-containing beverages, decreased television viewing time, a low-fat diet, and increased activity. 30 Other experts target the high-risk period from 25 to 35 years, menopause, and the year after successful weight loss. The current recommendation is that treatment is indicated in all individuals who have a BMI of 30 or higher or who have a BMI of 25 to 29.9 or a high waist circumference plus two or more risk factors. 31 Treatment should focus on individualized lifestyle mod- ification through a combination of a reduced-calorie diet, increased physical activity, and behavior therapy. Before treatment begins, an assessment should be made of the degree of overweight, the person’s eating habits, the person’s physical activity level, and the presence of obesity-associated risk factors and complications. 31 It also is advisable to determine the person’s barriers and readiness to lose weight. Dietary therapy should be individually prescribed based on the person’s overweight status and risk pro- file. 30 The diet should be a personalized plan with real- istic goals that are 500 to 1000 kcal/day less than the current intake. The aim should be for weight loss ini- tially, followed by a strategy for weight maintenance. Many popular diets exist such as Atkins, Ornish, Weight Watchers, and South Beach. A recent study comparing several of these diets suggested that adherence to the diet, not the diet itself, is most closely associated with weight loss (i.e., the best diet is the one the person likes best). 32 There is convincing evidence that increased physical activity decreases the risk of overweight and obesity. In addition, it reduces cardiovascular and diabetes risk beyond that achieved by weight loss alone. Although physical activity is an important part of weight loss therapy and helps with maintaining weight loss, it does not independently lead to a significant weight loss. 33 It may, however, help reduce abdominal fat, increase cardiorespiratory fitness, and prevent the decrease in muscle mass that often occurs with weight loss. Exercise should be started slowly with the duration and intensity increased independent of each other. Techniques for changing behavior include self-monitoring of eating habits and physical activity, stress management, stimulus control, problem solving, contin- gency management, cognitive restructuring, social sup- port, and relapse prevention. 30 Pharmacotherapy and surgery are available as adjuncts to lifestyle changes in individuals who meet specific criteria. Pharmacotherapy is usually considered only after combined diet, exercise, and behavioral therapy have been in effect for a reason- able period of time. Weight loss surgery is usually lim- ited to persons with a BMI greater than 40, those with a BMI greater than 35 who have comorbid conditions and in whom efforts at medical therapy have failed, and those who have complications of extreme obesity. However, more recent studies have shown the potential