Obesity Study

obesity imageDefinition and Epidemiology of Obesity

Preventive Services Task Force recommends that adult patients be screened for obesity by calculating BMI. The BMI is the patient’s weight in kilograms divided by height in meters squared. BMI calculations are a noninvasive, reliable, and low-cost screening tool for diagnosis and early counseling and behavioral interventions and may lead to improved outcomes. The National Institute of Health and the World Health Organization have established criteria for the diagnosis of obesity using the body mass index (BMI). Overweight is defined as a BMI of 25 to 29.9 and obesity as a BMI of 30 or higher. Obesity is further divided into three classes: class I (BMI 30-34.9), class II and class III (BMI >40). Severe, or morbid, obesity is defined as class III obesity or class II obesity in the presence of significant comorbidities caused by obesity (BMI 35-39.9) .

Obesity increases risk of chronic disease and overall mortality. The magnitude of risk generally rises with the degree of obesity. In a large study of middle-aged patients, mortality was assessed after adjustment for chronic disease and smoking. The mortality risk among obese patients was 200% to 300% higher than those with a normal BMI.

The distribution of adipose tissue is important. Abdominal obesity is associated with increased risk of coronary artery disease, type 2 diabetes mellitus, dyslipidemia, and hypertension. In adults with a BMI of 25 to 34.9, a waist circumference greater than 102 cm (40 in) for men and 88 cm (35 in) for women is associated with greater risk than that determined by BMI alone. Waist circumference is measured with a flexible tape placed horizontally around the abdomen at the level of the iliac crest.

Evaluation for Underlying Causes of Obesity

Obese patients should be screened for secondary diseases, medications, and behavioral conditions that can cause or worsen the condition. The time course over which the obesity developed, the patient’s eating habits, and a medication and psychiatric history are important in initial evaluation. Life events commonly associated with weight gain include pregnancy, marital status changes, occupational changes, and smoking cessation. A careful history and physical examination should determine the extent of testing for secondary causes of obesity and obesity-related diseases.

Medications can cause weight gain. In patients with diabetes, thiazolidinediones, oral hypoglycemic medications, and insulin can all cause modest weight gain. Certain psychiatric medications, including tricyclic antidepressants, selective serotonin reuptake inhibitors, lithium, and many antipsychotic agents are also associated with weight gain.  Endocrine disorders could be the underlying cause in secondary obesity. The reduced metabolic activity of hypothyroidism may result in weight gain. Excess glucocorticoids from iatrogenic or primary disease states leading to Cushing syndrome can also cause obesity. . Hypothalamic damage (by surgery, trauma, tumor, or inflammatory disease) growth hormone deficiency, polycystic ovary syndrome, insulinomascan also result in obesity.

Key Points

  • All adults should be screened for obesity by calculating BMI.
  • Mortality risk among persons with obesity is 2 to 3 times higher than for those with normal weight.
  • In adults with a BMI of 25 to 34.9, a waist circumference greater than 102 cm (40 in) in men and 88 cm (35 in) in women is associated with higher mortality risk than that determined by BMI alone.
  • Morbid obesity is defined as class III (BMI >40) obesity or class II (BMI 35-39.9) obesity in the presence of significant comorbidities caused by obesity.
  • A sustained weight loss of 5% to 15% will reduce the risk of many medical complications of obesity.
  • Physical activity programs without diet achieve only modest weight loss but are useful in maintaining lost weight and reducing abdominal fat, metabolic abnormalities, and cardiovascular risk.
  • Calorie restriction is effective for weight loss; however, dieting rarely causes more than 5 kg of sustained weight loss.
  • Pharmacologic therapy with sibutramine or orlistat should be considered in obese patients in whom behavioral interventions have been ineffective and may result in an additional 3 to 4 kg of weight loss.
  • Sibutramine should not be used in patients with poorly controlled or uncontrolled hypertension or cardiovascular disease.
  • Bariatric surgery should be considered in patients with a BMI greater than 40 and in those with a BMI greater than 35 who also have serious obesity-related comorbidities.

Behavioral Interventions

Behavioral therapies, including dietary and exercise interventions, are traditional and effective approaches to obesity therapy. They are often used to augment pharmacologic and surgical approaches in morbidly obese patients.

Behavioral interventions typically involve self-monitoring of food intake, learning about and controlling stressors that activate eating, establishing a supportive social network, slowing food intake during meals, nutrition education about portion size and meal content, goal setting and behavioral contracting, and education about appropriate physical activity. Group and individual therapy sessions are both effective but result in only modest weight loss—on average, 3 kg or less. Active monthly interventions with face-to-face or Internet engagement with patients can be effective in preventing weight from being regained.

Physical activity is often recommended for treatment of obesity and being overweight. Low-intensity workouts equivalent to walking 30 minutes per day are effective in maintaining stable weights; high-intensity/high-amount workouts provide proportionately greater benefits. Exercise has additional benefits of improved cardiovascular health .

Dietary Therapy

Restricting caloric intake is a key component of any weight loss program. Very-low-calorie diets of under 800 kcal/d are difficult to follow. The only VLCD program that we recommend is in conjuction with HCG protocol. The amount of ideal caloric restriction in patients depends on the patient’s age, sex, degree of obesity, and physical activity. Calorie-restricted diets generally fall into three major categories: balanced low-calorie diets, low-fat diets, and low-carbohydrate diets. Low-carbohydrate diets, including variants of the Atkins diet, target an initial goal of 20 g/d or less of carbohydrates for several months, followed by a goal of 50 g/d or less for subsequent continued weight loss and maintenance. Low-fat diets, such as the Ornish diet, generally restrict fat intake to 10% or less of total dietary calories. Balanced low-calorie diets, such as the Zone diet, have a balance of carbohydrate, protein, and fat, typically in a 40%/30%/30% distribution.

Comparisons between  low-fat to low-carbohydrate diets showed a short-term increase in weight loss with low-carbohydrate diets with no difference between the two types of diet after 12 months . Low-carbohydrate diets improve triglyceride and HDL cholesterol levels more than low-fat diets, whereas low-fat diets improve LDL and total cholesterol levels more than low-carbohydrate diets. In obese postmenopausal women for 12 months, a low-carbohydrate diet resulted in a mean weight loss of 4.7 kg, compared with 1.6 kg with a balanced low-calorie diet and 2.2 kg with a low-fat diet. HDL cholesterol, triglycerides, and both systolic and diastolic blood pressure were more favorable in the low-carbohydrate diet group.

Pharmacologic Therapy

Pharmacologic therapy can be offered to obese patients when diet and exercise alone has not been effective . It is important for patients to know the drugs’ side effects, the lack of long-term safety data, and the temporary nature of the weight loss achieved with medications prior to taking these medications.  The U.S. Food and Drug Administration has approved sibutramine for a 2-year course of therapy and orlistat for a 4-year course. In many studies, obesity medications should be used in combination with diet and exercise, as cessation of the obesity medication is associated with recurrent weight gain. Guidelines from the National Institute for Health and Clinical Excellence (NICE) recommend discontinuation of drug treatment if a 5% threshold in weight loss has not been reached by the end of 3 months of therapy.

Orlistat, which is available over the counter, inhibits pancreatic lipases and alters fat digestion. This results in dose-dependent incomplete digestion of fat with elimination of the excess fat in the stool. Less than 1% of orlistat is absorbed systemically, so it has few drug-drug interactions. Major side effects, occurring in up to 30% of patients, include abdominal cramping, flatus, oily stool, and fecal incontinence. A meta-analysis of 16 orlistat trials demonstrated an average weight reduction of 2.9 kg. The study also demonstrated that orlistat reduced the incidence of diabetes and improved glycemic control in patients with diabetes. Orlistat also reduces blood pressure as well as total cholesterol and LDL cholesterol levels and is associated with a small increase in HDL cholesterol level.

Sibutramine is a sympathomimetic agent that suppresses appetite and food intake.

Sibutramine trials demonstrated an average of 4.2 kg of weight loss compared with placebo. Sibutramine mildly increased concentrations of HDL cholesterol and lowered triglyceride levels. Sibutramine increased systolic blood pressure by an average of 1.7 mm Hg, diastolic blood pressure by 2.4 mm Hg, and pulse by 4.5/min. Other adverse effects occurred in up to 20% of patients and included insomnia, nausea, dry mouth, and constipation. Sibutramine should not be used in patients with uncontrolled or poorly controlled hypertension or a history of cardiovascular disease.

Surgical Treatment

A 1991 NIH consensus panel recommended that surgical therapy for obesity be considered in well-informed, motivated patients with a BMI above 40 who have an acceptable surgical risk and who have failed to benefit from  nonsurgical weight loss therapies. The goal of bariatric surgery is to improve mortality, reduce morbidity from obesity-related illnesses, and improve patient quality of life. The panel also suggested that adults with a BMI above 35 with serious comorbidities, such as diabetes, sleep apnea, obesity-related cardiomyopathy, or severe joint disease, may be considered for surgery. Bariatric surgery in elderly patients and children remains controversial.

Restrictive bariatric procedures reduces gastric size and leaves small-bowel absorptive function intact. Caloric intake is reduced by causing early satiety. These procedures are simpler and less invasive but produce less long-term weight loss. Vertical banded gastroplasty and laparoscopic adjustable gastric banding are examples of restrictive procedures.

Procedures utilizing malabsorption shorten the length of functional small bowel and induce more dramatic weight loss, but at the cost of an increased risk of nutritional deficiencies. These procedures may be combined with restrictive approaches. The Roux-en-Y gastric bypass is a dual-mechanism bariatric surgery combining a small gastric reservoir, which restricts oral intake, with a small-bowel bypass, which induces mild malabsorption. The two most common types of bariatric procedures performed are laparoscopic adjustable gastric banding and Roux-en-Y gastric bypass.

Patients who underwent gastric banding lost  approximately 48% of excess weight, and those who underwent gastric bypass lost approximately 60% to 70% of excess weight. These patients demonstrated improved or resolved diabetes, hyperlipidemia, hypertension, and obstructive sleep apnea after bariatric surgery . Another study of obese patients (men with BMI >34 and women with BMI >38) compared bariatric surgery outcomes to conventional (nonsurgical) treatment outcomes over an 11-year period. In conclusion, weight losses from baseline were 25% for gastric bypass and 14% for gastric banding. When adjusted for age, sex, and comorbidities, the surgical group had 29% reduction in mortality compared with the control group.

The mortality rate of bariatric surgery is generally less than 1%, but post-op complications and adverse effects are common. Complications of gastric banding procedures include intractable nausea and vomiting, staple line disruption, stomal obstruction, band erosion , and severe gastroesophageal reflux disease. Complications of gastric bypass include bleeding, anastomotic leaks, wound infections, ventral hernias,  stomal stenosis, cholelithiasis and vitamin deficiencies. Nutritional deficiencies of vitamin B12, iron, calcium, folic acid, and 25-hydroxyvitamin D are common in patients after gastric bypass. Less frequently, deficiencies of magnesium, copper, zinc, vitamin A, other B-complex vitamins, and vitamin C may occur. Pulmonary embolism is a common but preventable complication in bariatric surgery.


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