Discussion
Approximately 35% of women and 31% of men age 20 years and older are overweight or obese. One-fourth of children and adolescents ages 6 to 17 years is considered overweight or obese (1). The prevalence of overweight and obesity in the United States has increased substantially. The increase in overweight Americans rose from 25.4% (second National Health and Nutrition Examination Survey [NHANES II]) in 1976 to 1980, to 33.3% (NHANES III) in 1988 to 1991. In 1998, an estimated 97 million adults in the United States are considered overweight or obese — 55% of the population (3). Obesity contributes to many adverse health outcomes, including type 2 diabetes; cardiovascular disease; hypertension; stroke; osteoarthritis; gallbladder disease; sleep apnea and respiratory problems; and endometrial, breast, prostrate, and colon cancers . Obesity-related conditions are estimated to contribute to 300,000 deaths yearly, ranking second only to smoking as a cause of preventable death. The total cost of obesity amounted to $99.2 billion in 1995, with $51.6 billion being direct medical costs.
Obesity is the result of a positive energy balance; energy intake exceeds energy expenditure. Several lifestyle factors, including excessive energy intake, fat intake, and physical inactivity, are associated with the pathophysiology of obesity. Growing evidence suggests a strong link between genetic factors and the pathogenesis of obesity. Genes involved in energy regulation like leptin, a signal protein for satiety produced in the adipose tissue, and other hormones or peptides, such as neuropeptide Y, may have important implications for understanding the causes of obesity . Ongoing research is required to determine the role of genetic factors in obesity treatment.
Adults (Age 18 years and Older)
The body mass index (BMI) is most frequently used to classify an adult’s degree of overweight or obesity. A BMI is calculated by dividing weight in kilograms by height in meters squared. BMI = weight (kg)/ height (m2).
The BMI is correlated with body fatness. Several studies have indicated the relationship between an elevated BMI and an increased incidence of morbidity and mortality. According to the Dietary Guidelines, the cutoff for a healthy weight for both men and women is a BMI of 25 kg/m2. Studies have demonstrated that morbidity increases significantly above a BMI of 25. A BMI of 25 to 29.9 kg/m2 is considered overweight. Obesity is defined as a BMI of 30 kg/m2 or more (3). Guidelines established by the American Obesity Association suggest determining BMI-related health risk not only based on the BMI but also by evaluating the presence of comorbid conditions and/or other risk factors that place individuals at an increased health risk. For more information on these guidelines, refer to the Weight Management Protocol Disease Management Decision Chart in Medical Nutrition Therapy Across the Continuum of Care: Supplement 1 .
The presence of excess fat in the abdomen out of proportion to total body fat is an independent predictor of increased risk and morbidity. Evidence from epidemiologic studies shows waist circumference to be a better marker of abdominal fat content than the waist-to-hip (WHR) ratio; waist circumference also is the most practical anthropometric measurement for assessing a patient’s abdominal fat content before and during weight-loss treatment (3). However, these waist circumference measurements lose their incremental predictive power in patients with a BMI of 35 kg/m2 or more because these patients will exceed the cutoff points.
Children and Adolescents
In the United States one child in five is overweight, and the number of overweight children continues to grow. Over the last two decades, this number has increased by more than 50%, and the number of “extremely” overweight children has nearly doubled (8). The classification of overweight for children is determined by plotting the height and weight on growth charts. The height and weight growth charts developed by the National Center for Health Statistics (NCHS) are most commonly used. The NCHS weight-for-height curve is appropriate for the prepubescent child. The NCHS is a valid measure for overweight (greater than the 90th percentile) females younger than 10 years and males younger than 11.5 years (9). However, it is not useful to assess weight for height in an adolescent. Body mass index (BMI) percentiles are suggested to assess weight for height in adolescents. For individuals 6 to 17 years of age, the third National Health and Nutrition Examination Survey (NHANES III) study defined overweight as a body mass index (BMI) exceeding the 95th percentile for BMI for those of the same age and sex. The American Medical Association’s Guidelines for Adolescent Preventative Services recommend that if the BMI percentile is greater than 95, the child is overweight, and if the BMI percentile is 85 to 95, the child is at risk for overweight .
Children with a body weight greater than the 85th percentile should be referred to a second-level screen to determine underlying causes. The second-level screen includes family history, blood pressure, total cholesterol, in-depth diet history, and behavioral and environmental assessment. An in-depth medical assessment is recommended for children at or above the 95th percentile (7,11).
After the adolescent’s height and weight are measured, the BMI can be calculated, as described above. Once the BMI is determined, use the appropriate chart below to determine whether the adolescent needs further evaluation or counseling regarding his or her weight. The BMI should not be calculated if the adolescent has disabilities that confound measurements of height or weight.
Like adults, children and adolescents who are obese have an increased risk for vascular disease. Likewise, children and adolescents who are overweight have a higher incidence of high blood pressure and high cholesterol. The risk for overweight children remaining overweight in adulthood is strongly correlated. Weight gain among children and adolescents is attributed to a combination of poor dietary habits, family lifestyle, physical inactivity, ethnicity, socioeconomic status, and genetic makeup. Obesity is more prevalent among girls and Hispanic, African American, and American Indian children (8). Parenteral obesity of at least one parent more than doubles the risk of a child’s obesity in adulthood, whether or not the child is obese (12).
Early intervention is recommended. The goal of treatment is not weight loss, but to slow the rate of weight gain so that children and adolescents grow into their adult weight. Overweight children should not be put on restrictive diets. Children and adolescents must receive adequate vitamins, minerals, protein, and energy to maintain healthy growth. Governmental dietary guidelines currently recommend that children older than 2 years of age gradually begin to adopt a diet that, by age 5, contains no more than 30% of energy from fat. A diet low in fat, saturated fat, and cholesterol (less than 300 mg/day) is encouraged for most school-age children and adolescents.
Adequate exercise also is encouraged. The US Surgeon General’s Report on Physical Activity and Health recommends 30 minutes a day of moderate to vigorous physical activity for children and adults
Adults
Weight management is defined as the adoption of healthful and sustainable eating and exercise behaviors indicated for a reduced risk for disease and for improved feelings of energy and well-being (17). A nonrestrictive approach to eating based on internal regulation of food (hunger and satiety), exercise, and healthful eating habits should be emphasized. The probability of long-term maintenance of weight loss and goals is increased in persons who exercise regularly, use social support to maintain eating and exercise habits, view their eating and exercise regimens as a permanent lifestyle, and do not allow lapses to deter them from their lifestyle (3,6). The recommended minimum energy level is 1200 kcal/day for women and 1400 to 1500 kcal/day for men (3,18). Recent evidence suggest moderation in total energy is the key variable in promoting weight loss (18).
Energy: Energy requirements should be based on individual needs to promote gradual weight loss. Consideration of a realistic energy goal is important for successful patient compliance with a weight-management program. It is recommended that the rate of weight loss be 0.5 to 1.5 lb/week. The recommended minimum energy level is 1200 kcal/day for women and 1500 kcal/day for men .
Protein: To preserve lean body mass, intake should be 0.8 to 1.2 g of dietary protein per kilogram of body weight .
Fat: Fat should be 20% to 30% of total energy. Limit saturated fats to less than 6% to 8% of fat calories. Findings of the U.S. Department of Agriculture have found that diets low to moderate in fat (15% to 30%) tend be lower in total energy and highest in diet quality when compared to low carbohydrate diets (< 0%) .
Carbohydrates: Carbohydrates should make up 50% to 60% of total energy. Selecting sources high in fiber is recommended, for example, fruits, vegetables, whole grain breads, cereals, and legumes. Consumption of 20 to 35 g of fiber daily has been demonstrated to reduce energy density of food consumed and promote satiety by delaying gastric emptying (20). Findings of the U.S. Department of Agriculture have found that diets high in carbohydrate (>55%) and low to moderate in fat (15% to 30%) tend be lower in total energy and highest in diet quality when compared to low carbohydrate diets (<30%) .
Exercise: The US Surgeon General’s Report on Physical Activity and Health recommends 30 minutes of moderate to vigorous physical activity per day for children and adults (16). Increased physical activity should be a key component of a weight-loss program (3,17). A combination of weight resistance or strength training and aerobic exercise is recommended to preserve lean body mass and promote the loss of adipose tissue.
Behavior modification: Behavior modification is an integral component of weight loss and weight management and should be combined with a healthy eating plan to achieve optimal outcomes (17). Behavior modification is based on the premise that eating is a conditioned response. A goal of behavior modification is to help the patient realize and eliminate the associations that control eating behavior.
Very-low-calorie diets (VLCD): These specialized feeding regimens provide less than 800 kcal/day and are recommended only to patients who are at a very high health risk related to obesity. Criteria for these regimens are a BMI greater than or equal to 30 with no comorbidities or risk factors, or a BMI greater than or equal to 27 with comorbidities or other risk factors (1). Individuals on a VLCD should be under the supervision of a physician. The typical treatment duration is 4 to 6 months. Patients provided less than 800 kcal/day are at risk for protein, vitamin, and mineral deficiencies.
High-quality protein (0.8 to 1.5 g/kg of ideal body weight [IBW] per day) and a minimum of 50 g of carbohydrate should be provided. Depending on the formulation and regimen used, vitamin and mineral supplementation may be needed (1). People with a history of gallbladder disease, cardiac abnormality, cancer, renal or liver disease, type 1 diabetes, or HIV should use these regimens with caution. Studies have shown that weight loss as much as 20 kg over 12 to 16 weeks have provided significant improvements in diabetes, hypertension, and cardiovascular conditions when using VLCD regimens (1). However, weight is gradually regained after treatment, and the long-term outcome of VLCD has demonstrated that most individuals regain all the weight they lost within 5 years of stopping the diet .
Pharmacotherapy: The pharmacologic agents currently available for obesity intervention are designed to contribute to energy deficit through a variety of mechanisms (21). Fenfluramine (Pondimin) and dexfenfluramine (trade name Redux) have been voluntarily withdrawn from the market because of reports of their association with valvular heart disease. They are serotoninergic agents and act primarily by increasing serotonin levels in the brain, leading to a decrease in appetite.
Cathecholaminergic drugs, such as phentermine and phentermine resin (Adipex-p, Fastin, and others), which frequently are prescribed with fenfluramine and dexfenfluramine, have a different mechanism of action and still remain available. They decrease appetite and food intake by increasing the availability of norepinephrine in the brain. Merida, a centrally acting agent, is classified as a selective serotonin and norepinephrine reuptake inhibitor; it does not stimulate release of neurotransmitters. Merida seems to reduce body weight by modifying intake through increased satiety, and animal data suggest that it may also raise energy expenditure by stimulating thermogenesis (22). Xenical, a pancreatic lipase inhibitor, is the first obesity medication that acts nonsystemically. Patients should take this medication with meals, as it takes effect within 2 hours of ingestion. Patients receiving Xenical should follow a moderately low-fat diet (less than 30% fat of total energy), with fat distributed evenly at each meal. Side effects may include gas, oily leakage, and diarrhea.
Criteria for pharmacotherapy include a BMI of 30 or more with no comorbid conditions, or BMI of 27 or more with comorbid conditions and/or a very high health risk (3). Complications include dry mouth, nausea, headache, and insomnia (1,3,17,21), increased blood pressure, and increased heart rate. Patients who should avoid this regimen for weight loss are those with unstable cardiovascular disease, are under 18 years of age, are pregnant or lactating, or are receiving monoamine oxidase inhibitors (MAOIs), antidepressants, or migraine medications. Medical nutrition therapy, exercise, and behavior modification should be provided in adjunct to pharmacotherapy . Studies demonstrate that individuals receiving anorexiant medications lose on average 0.5 lb/week (1). Weight loss plateaus by 6 months, and weight regain occurs after medication therapy stops. A limited number of studies have evaluated the safety and efficacy of anorexiant medications for more than 2 years. The physician must continually assess drug therapy for efficacy and safety.
Surgery: Weight loss surgery is one option for weight reduction in a limited number of patients with severe obesity: those with a BMI greater than or equal to 40 or a BMI of 35 or more with comorbid conditions (3). Roux-en-Y gastric bypass and vertical banded gastroplasty are the most commonly performed and widely accepted surgical procedures for weight loss (3,17). The primary benefit of surgical therapy is durable weight loss and maintenance of weight loss (1). The average weight loss associated with gastric reduction surgery is 40% to 75% of excess body weight, which correlates to approximately 30% to 40% of initial weight (1). Most weight loss occurs in the first 6 months and continues for up to 18 to 24 months. The initial 6 months is marked by the most rapid weight reduction and improvements in comorbid conditions. Prospective studies show that the average weight 10 years after surgery is approximately 55% of excess body weight, with a weight regain of 10% to 15% of the initial weight lost (23). Criteria for surgical intervention for weight loss includes a BMI of 40 or more with no comorbid conditions or health risk, or a BMI greater than or equal to 35 with comorbid conditions or health risks (1,3) or a body weight 100 lb over IBW. A preoperative behavior change program is highly recommended. Complications include those associated with any surgery, gallstones, nutritional deficiencies requiring supplementation, and the dumping syndrome. Refer to Gastric Reduction Surgery for Obesity earlier in this section.
