Obesity and Weight Management

Diet, Excercise, Medications, and Surgery

Obesity is both preventable and treatable. 

What is obesity and how do we measure its impact on health?

Obesity is an excess of body fat. Although several sophisticated tools can accurately measure body composition, obesity is defined most commonly by the body mass index (BMI).  The BMI is the weight divided by the height squared in the metric system:  kilograms per square meter.  BMI correlates very closely with total body fat and with obesity-related illnesses and excess mortality.  A BMI less than 18.5 kg/m2 is underweight, 18.5-24.9 kg/m2 is normal, 25.0 – 29.9 kg/m2 is overweight, and greater than or equal to30.0 kg/m2 is obesity.  In the United States, approximately 30% of adults are obese and another 35% are overweight.


The impact of obesity on health is affected by several factors in addition to BMI.  These include: the total amount of excess fat; the location of excess fat; an individual’s

age, race, and ethnicity; the presence or absence of obesity-related metabolic abnormalities, and; an individual’s level of fitness.  As might be expected, severe obesity (BMI greater than 40 kg/m2) is associated with more obesity-related illnesses and premature mortality than less severe obesity BMI (30-39.9 kg.m2).  In general, excess fat in the upper body, and particularly in the abdominal cavity surrounding vital organs, is associated with more obesity-related abnormalities than is excess fat in the lower body and fat located just under the skin.


Age is an important predictor of the impact of obesity on health.  Overweight children and adolescents have an increased risk of becoming obese as adults. Metabolic abnormalities are less common than in adults, but as obesity in children has become more common so have obesity-related illnesses, including diabetes mellitus type 2.  The impact of obesity in adults increases with age, until about age 80.  Severe obesity is a less common cause of premature death in the elderly.  By the ninth decade, being underweight is actually a more important predictor of excess mortality. Race and ethnicity may also play a role. For example, Asians with only modest amounts of excess fat may have more health consequences than individuals from other backgrounds with a similar BMI.  Conversely, African-Americans can have higher BMIs and still have weights associated with the lowest risk of illness.

Individuals with equal BMIs may also have different risks of developing obesity-related metabolic abnormalities and metabolic illnesses.  This is most likely due to genetic factors that are not yet fully identified. For example, some overweight individuals may have significant abnormalities in their blood lipids, blood pressure, and blood sugar while other individuals with an identical BMI might not.

An individual’s ability to exercise (their “fitness”) is also an important predictor of illness and early death in overweight and obese individuals.  Individuals who are sedentary and not “fit” are more likely to develop obesity-related illnesses and early death than those who are fit.  Those that are both obese and not fit have an even greater risk.  Most interestingly, however, individuals who are obese but able to exercise effectively have a markedly reduced risk.  This relationship between fitness and obesity will be discussed in greater detail below.

Obesity is associated with illnesses that affect almost every body system.  These include coronary heart disease (the cause of most excess mortality associated with obesity), certain cancers (colon, ovary, and breast), diabetes mellitus type 2, hypertension, lipid disorders, and the metabolic syndrome.  Obesity is also commonly associated with degenerative joint disease (of weight bearing joints), diseases of the gastrointestinal tract including gastroesophageal reflux disease (GERD) and gallbladder disease, thromboembolic disorders, cerebrovascular diseases, congestive heart failure, respiratory impairment including sleep apnea, and a variety of disorders of the skin.  Obesity is also associated with a greater risk of surgical and obstetric complications. Major depression and binge eating disorder are also more common in the obese. Several studies suggest a greater risk of social discrimination in the obese than in individuals of normal weight.  Of note, osteoporosis is less common in the obese.

The marked increase in the prevalence of obesity in the United States and most other parts of the world is associated with a marked increase in obesity-related illnesses, particularly diabetes mellitus type 2. However, recent studies published by the Centers for Disease Control (CDC) using data from the National Health and Examination Study (NHANES) have suggested that the impact in an individual person with obesity may be less severe than previously estimated.1  On average, a BMI of 30 – 34.9 kg/m2 is associated with a 20% increase in mortality from all causes and a BMI between 35-39.9 kg/m2 is associated with an 80% increase. These authors have also suggested that being overweight, BMI 25.0 – 29.9 kg/m2, is not associated with excess mortality at all.


Deciding to Lose Weight    


Once obese, it is difficult, albeit clearly possible, to return to a normal body weight.  Thus, prevention of obesity should be the priority for both individuals and for society at large. Unfortunately, in most Western cultures the availability of calories and obstacles to energy expenditure are overwhelmingly common. Without a conscious strategy to maintain one’s weight, it is common to gain weight as one ages. Principles discussed below associated with successful weight maintenance should also be used by those who have never been overweight to prevent unintended weight gain. 

Although a return to normal weight is uncommon, most obesity-related disorders will benefit from modest amounts of weight loss. It has been estimated that weight loss of 5-10% of initial weight together with increases in physical activity can decrease the risk of diabetes and other illnesses in half.  Thus, weight loss (and increases in physical activity) can be seen as a treatment option for almost any obesity-related disorder. Many individuals will also desire weight loss for psychological, social, or cosmetic reasons.  Selecting a specific weight loss strategy should include a balance of the benefits and potential harms in each instance.

Not all individuals who would benefit from weight loss are “ready” to change behavior. Readiness to change can be assessed with the Transtheoretical Model of Change (also commonly called the Stages of Change model). Although initially developed for use in smoking cessation, this approach is also useful in changing eating and exercise behaviors. In this model, individuals can be identified as being in one of various stages associated with behavioral change:  precontemplation, contemplation, preparation, action, maintenance, and relapse. Different behavioral change strategies can be applied during each stage in an attempt to move individuals to the next stage.


Weight Loss Diets 

The goal of any weight loss diet is to achieve a daily energy intake that is lower than daily energy expenditure. Daily energy expenditure can be estimated utilizing common formulas based on age, gender, and height. Adjustments can be made based on physical activity. A useful web site to help calculate energy expenditure and develop personalized eating plans has been developed by the United States Department of Agriculture    

Most weight loss programs try to create a daily deficit of 500 calories.  Because a pound of fat is equivalent to 3500 calories, this deficit will result in a weight loss of one pound per week. For example, a person who requires 1800 calories per day to maintain their current weight would need to ingest 1300 calories per day in order to lose one pound per week.


Studies of weight loss diets, most often done in University-based programs, typically suggest an average weight loss of between five and ten percent of the starting weight in six to 12 months of follow-up. That is, a person starting a diet at 200 pounds will lose between 10 and 20 pounds. All studies, however, show a wide variation among individuals.  While many patients are near the average, some patients lose substantially more. Adherence to the diet program is a more important predictor of success than the diet composition or type.  Community-based programs are also associated with successful weight loss with wide variation among individuals.  Weight Watchers™, for example, has reported a 3.2% average weight loss with two years of follow-up.2

Much of the controversy about weight loss diets over the last several years has focused on the ideal macronutrient composition (proportion of fat, carbohydrate, and protein) of the diets.  In fact, differences in macronutrient composition have been the basis of popular weight loss diets for decades, particularly diets that have advocated low intakes of carbohydrates.

Traditionally, recommendations for weight loss diets have paralleled those for weight maintenance and “healthy diets.”  Such diets have traditionally recommended lower fat intakes as the primary macronutrient strategy for achieving lower calories. Although recommendations have been somewhat liberalized in the last several years, current Dietary Guidelines (/DietaryGuidelines) published by the U.S. Department of Health and Human Services and the Department of Agriculture continue to recommend fat intakes between 20-35% of total calories along with carbohydrate and protein intakes of 45-65% and 20-35% of total calories respectively.  This macronutrient composition is also consistent with the DASH Eating Plan originally developed for treating high blood pressure as well as with diets recommended for treatment of lipid disorders and diabetes.  Most vegetarian diets and  Mediterranean-style diets also fall within this range and can be designed to achieve an energy deficit for weight loss.

A key feature of macronutrient-balanced weight loss diets is close attention to portion size.  The marked increase in portions consumed by Americans, particularly in fast food and other restaurants is well documented.  Close contact with dieticians and other health professionals is essential for patients to learn how to estimate portion sizes and calorie content, as well as methods to increase physical activity and to provide support.  The Diabetes Prevention Program, for example, provided subjects with 16 one-hour visits to help them master the comprehensive program. 3  Food models that illustrate portion sizes and use of prescribed Diet Plate and Breakfast Bowl may also be helpful. 4

Recent studies have investigated the merits of diets that are lower in total carbohydrate. These diets typically have higher proportions of fat and/or protein. The Atkins Diet™ and the South Beach Diet™ are examples of diets that restrict carbohydrate.  Dozens of clinical studies have compared diets with different levels of carbohydrate for their effectiveness in weight loss.  These studies consistently show roughly equal amounts of weight loss between the two diet approaches.  Despite the higher proportion of fat in the low carbohydrate group, few significant differences in blood cholesterol, blood sugar, or other important metabolic parameters are observed between the two diet types.  Similar results have been shown with comparisons of other popular diets including the Zone™ and the low-fat Ornish program. The primary predictor of weight loss in these studies is adherence to the dietary program, not the type of diet. 5, 6

Another important approach to weight loss diets is the use of meal replacements.  These are low calorie diets in which all or most food is provided by the weight loss plan.  These can be as pre-packaged meals or as combinations of bars, shakes, and soups.  Meal replacement programs assist some patients by eliminating many of the decisions related to food planning, food preparation, and portion control.  In this manner, it may easier to achieve calorie restriction for some individuals. Although most meal replacement programs also aim for a 500-calorie per day energy deficit, greater restriction can be achieved.  When such diets provide less than 800 calories per day they are known as very-low calorie diets (VLCDs).  VLCDs have been shown to result in greater initial weight loss, closer to two pounds per week, than typical low calorie diets (LCDs). On average such programs result in 15% of initial weight lost at one year, again with a wide variation among individuals. Comparison between 400, 600, and 800 calories per day has demonstrated that 800 per day is safer and equally effective.

The long-term effectiveness of VLCDs, compared to LCDs, is variable. Although some studies show improved long-term maintenance of weight loss, most studies suggest that the two approaches are equivalent over years of follow-up.

Nonetheless, the more rapid pace of weight loss that can be achieved with VLCDs makes them very useful in clinical circumstances in which rapid weight loss is particularly useful.  Examples include weight loss prior to surgery including orthopedic surgery, transplant surgery and bariatric surgery), very poorly controlled diabetes mellitus type 2, and other obesity-related disabling conditions. VLCDs should be used in comprehensive programs that offer close medical supervision as well as interprofessional services to assist with increases in physical activity, behavioral therapy, and social support.  Patients who successfully lose large amounts of weight rapidly may have important unexpected psychological concerns that need to be addressed.  Special attention must also be placed on the transition back to normal diets to prevent weight regain.

Weight Maintenance

Although many dietary approaches can help lose weight, weight loss is only useful in the long term if it can be kept off.  Numerous studies have tried to describe the behaviors that are most predictive of weight maintenance.  The most important is the National Weight Control Registry (NWCR). 


The NWCR was established in 1994 to examine the behaviors of successful weight losers. To enter the registry, one most have lost at least 30 pounds and kept it off for one year. In fact the 5,000 registrants have lost over 65 pounds and kept it off for over five years.  The average starting BMI was 36.7 kg/m2 and the current BMI is 25.1 kg/m2.

Several key factors define this group of successful weight losers. First, NWCR members continue to eat a low calorie diet, typically less than 1400 calories per day. On average, fat intake is low, equaling less than 30% of calories. Interestingly though, those patients who restrict carbohydrate have also been successful in maintaining their weight loss.  Second, members engage in very high levels of physical activity totaling almost 2700 calories per week.  This is equivalent to moderate exercise, such as a brisk walk, for one hour per day, six days per week.  Third, they monitor their weight regularly.  Over two-thirds weigh themselves daily or weekly.  NWCR members also limit television viewing, maintain dietary consistency on the weekends, eat breakfast regularly, and rarely eat fast food.


Exercise for Weight Loss and Weight Maintenance


Aerobic exercise has a complex, important relationship to weight loss and weight maintenance. Aerobic exercise without concurrent dietary changes has a very modest role in weight loss.  Similarly, exercise plus dietary changes compared to diet alone leads to very modest increases in weight loss, approximately one extra kilogram. The effect, however, is increased by both increased intensity of exercise and increased duration.

Despite the absence of large amounts of weight loss with exercise, metabolic factors consistently improve. Elevations in blood pressure, blood lipids (especially blood triglycerides, HDL-cholesterol) and blood sugar all improve with exercise. Here, too, the effect is increased with greater intensity and duration of exercise.

As discussed above, the NWCR suggests that even though exercise is not an essential factor for weight loss, it is one of the key predictors of successful weight maintenance.

Most importantly, regular aerobic exercise is associated with striking improvements in obesity–related illness and premature death.  One large study, for example, studied individuals with different body weights and different amounts of fitness (as measured by formal exercise testing). 8  Individuals who were obese and not fit had a three-fold increase risk of death after 14 years of follow-up as compared to individuals who were normal weight and fit.  Most interestingly, individuals who were obese but fit had an indistinguishable death rate from the normal weight and fit group. This study, and several others done more recently, suggest that fitness can decrease the risk of the negative health effects of obesity.


Behavior Therapy and Social Support  


Successful weight loss, weight maintenance, and increased physical activity require sustained changes in behavior.  Behavior therapy has been shown to be a useful tool in changing both eating and exercise behaviors.  Behavior therapy can be implemented individually or in groups. Psychologists, dieticians or other health professionals typically lead formal programs. Many skills can also be learned less formally. Controlled studies demonstrate a significant increase in weight loss with behavioral therapy compared to controls.

Behavior therapy relies on specific strategies to change problematic behaviors. Weekly goal setting creates a sense of self-efficacy and can be useful in reinforcing further change. Self-monitoring includes tracking food and beverage intake and physical activity.  Recording the setting and emotional state associated with the behavior may allow specific factors to become targets for change. Stimulus control requires identification of both food and non-food cues that increase both desired and unwanted behaviors. Simple strategies such as keeping certain foods out of the home may be helpful.  Cognitive restructuring such as identifying obstacles to success and identifying specific solutions may be helpful for some individuals.  Dysfunctional thoughts that interfere with goals are replaced with more rational thoughts. Formal cognitive behavioral therapy with a trained psychologist can facilitate these processes.

  Social support is also an important part of most successful weight management programs. Peer support, diet partnerships, family involvement, and close contact with weight loss professionals have all been shown to be effective.

Medications for Obesity

Numerous medications are widely available for weight loss. Medications, including both FDA-approved and non-approved medications, can be obtained over-the counter, on the Internet, and by physician prescription. Numerous randomized clinical trials have compared medications to placebos for the treatment of weight loss.  Overall, medications result in 3-5% more weight loss (from initial body weight) than placebos.10  Most of these studies have been limited to patients already following well-structured lifestyle modification programs. Weight loss in less highly selected patients is likely to be lower.  Few studies have directly compared multiple medications, but on average there does not appear to be a significant advantage of one drug over another.   


Prescription medications for weight loss in the United States include highly restricted (Drug Enforcement Administration schedule II and III) medications such as various amphetamines, benzphetamine, and phendimetrazine. Most obesity experts agree that there is no role for such medications in treatment of obesity.  More commonly used medications include phentermine, diethylproprion, mazindol, sibutramine and orlistat. Only the latter two are approved by the FDA for longer-term use (one or two years). Orlistat, at half the prescription dose, is also available over-the-counter in the United States.

Regular use of weight loss medications, combined with lifestyle changes, results in modest amounts of weight loss (3-5% of initial body weight) and modest improvements in obesity-related metabolic factors.  Longer studies, however, demonstrate that weight is typically regained after discontinuation of the medication.  This has led some experts to suggest that obesity medications should be continued long term, analogous to treatment of other chronic conditions like hypertension, lipid disorders, and diabetes. To date, however, there are no clinical studies that demonstrate that such an approach improves obesity-related health outcomes and the FDA has not approved these medications for use in this manner.

Many other classes of medications are under investigation for weight loss.  Most notable has been rimonabant, a cannabinoid receptor blocker.  This medication, similar to other weight loss medications, results in an average weight loss of 5% of initial weight.  Unfortunately, the drug was associated with increased reports of depression and suicidality.  The medication was withdrawn from sales development in the United States in June 2007.


Surgery for Weight Loss

Multiple surgical procedures are now available to treat severe obesity. In fact, surgery for obesity is one of the fastest growing operations in the world. Practice guidelines of the U.S. National Institutes of Health define surgery as a treatment option for patients with a BMI greater than or equal to 40 kg/m2 and for patients with BMI greater than or equal to 35 kg/m2 with co-morbid conditions.  This makes well over 5% of the U.S. population eligible for what is known as bariatric surgery.

Bariatric procedures are designed to produce weight loss by two basic methods. Restrictive procedures, including gastric banding, gastroplasty, and most gastric bypass procedures, make the stomach smaller and lead to feelings of fullness.  Malabsorptive procedures interfere with nutrient absorption; they include biliopancreatic diversion, duodenal switch, jejunoileal bypass, and long limb gastric bypass.  Many centers in the U.S. have avoided malabsorptive procedures, despite excellent weight loss and patient acceptance, due to questions of long-term safety. The most common procedure in the United States, the roux-en-y gastric bypass, is typically performed to create both a restrictive and a modest malabsorptive component.  Most procedures in the U.S. are now performed laparoscopically (minimally invasive) and some can be done as outpatient surgery.

On average, bariatric surgery leads to substantially more weight loss than any other weight loss method.  The Swedish Obese Subjects Study, for example, followed 4047 patients for almost 11 years after surgery. 11  Gastric bypass patients had a maximum weight loss of 32% of their initial weight and 25% weight loss at the end of the study.  Vertical banded gastroplasty patients lost a maximum of 25%, with 16% at the end of 11 years. Laparoscopic banding led to 20% maximum and 14% at the study’s conclusion.

Weight loss surgery also leads to a marked reduction in obesity-related morbidity.  Substantial reductions are seen in diabetes control, lipid management, hypertension control, sleep apnea, and a variety of other clinical conditions.12  Results are proportional to weight loss. Procedures that lead to greater weight loss have more likelihood of leading to a complete resolution of each co-morbid condition.

Weight loss surgery, however, can also result in post-operative complications and death. Laparoscopic banding, for example, can result in prolapse (falling out of place) of the stomach through the band, infections of the reservoir, severe esophagitis, gastroesophageal reflux disease, and the need for conversion to a roux-en-y bypass.  Similarly gastric bypass procedures can result in bleeding, leaks, and infections. Vitamin and mineral deficiencies can occur, including deficiencies of fat-soluble vitamins A, D, E and K, vitamin B12, and minerals such as iron and calcium.

A meta-analysis of 136 published studies including 22,092 patients demonstrated an operative mortality (death rate) of 0.1% for gastric banding and gastroplasty, 0.5% for gastric bypass, and 1.1% for biliopancreatic diversion or duodenal switch.12 Data from community-based studies, however, suggest a higher mortality rate.13  Rates increase with age and with associated co-morbidities. In individuals between the age of 55 and 64 covered by Medicare, for example, the 30-day mortality rate is closer to 2%.  As a result, more surgeries in the United States are performed in women with private insurance who live in wealthier zip codes.  Such patients are likely at lower risk of complications, but also may receive less long term benefit of surgery.

The Swedish Obese Subjects Study has recently reported on overall long-term survival from obesity surgery. 14 Patients with surgery had a 24% reduction in death over 11 years compared to control patients. The absolute death rate, however, was low in both groups.  Approximately 850 patients need to have weight loss surgery to prevent one death per year.

Prevention of Obesity


Obesity and decreased physical activity are having a devastating impact on public health in the United States and much of the world.  Obesity is second only to cigarette use in causing preventable deaths.  Weight loss without surgery is difficult to achieve and maintain, and with surgery is expensive, complicated, and associated with its own risk.

Individuals can implement specific behavioral strategies to prevent weight gain. In general, such strategies are identical to those discussed above for weight loss and weight maintenance.  Basic principles such as consuming low calorie diets, performing high levels of physical activity most days of the week, and regular monitoring of weight are essential.  Limiting portion sizes, avoiding excess calories in beverages (both alcoholic and non-alcoholic), eating breakfast, avoiding fast food, and regular meal planning and record keeping are all useful tools.  In the United States, since weight gain with aging is the norm, most individuals will need a conscious weight maintenance strategy to prevent further weight gain.

Social policy changes, analogous to policies implemented to decrease tobacco use, are also necessary to have a substantial impact on obesity. 15

Some may perceive many of these as draconian, but there is little evidence that anything but dramatic social changes will be effective.  Proposals include selective taxes and subsidies for food grown, marketed and consumed; regulations on food advertisements; increased social marketing; enhanced labeling of caloric content of foods in markets and restaurants; changes in school lunch, food stamp, and beverage programs; more opportunities for physical activity at work, school and in the community; and a greater emphasis and investment in public transportation.


Weight Loss
Obesity and Weight Management