These clinical practice guidelines are designed to help physicians in their care of overweight and obesity, a growing public health problem that affects 97 million American adults -- 55 percent of the population.

These individuals are at increased risk of illness from hypertension, lipid disorders, type 2 diabetes, coronary heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea and respiratory problems, and certain cancers. The total costs attributable to obesity-related disease approaches $100 billion annually.

"Overweight and obesity pose a major public health challenge. The development of these guidelines was a pioneering achievement since they were the first ever developed by the Institute using an evidence-based model and methodology," said NHLBI Director Dr. Claude Lenfant. "This report will be an invaluable clinical tool for any health care professional who works with overweight or obese patients," he added.

The guidelines are based on the most extensive review of the scientific evidence on overweight and obesity conducted to date. The review involved a systematic analysis of the published scientific literature to address 35 key clinical questions on how different treatment strategies affect weight loss and how weight control affects the major risk factors for heart disease and stroke as well as other chronic diseases and conditions.

The guidelines present a new approach for the assessment of overweight and obesity and establish principles of safe and effective weight loss. According to the guidelines, assessment of overweight involves evaluation of three key measures--body mass index (BMI), waist circumference, and a patient's risk factors for diseases and conditions associated with obesity.

The guidelines' definition of overweight is based on research which relates body mass index to risk of death and illness. The 24-member expert panel that developed the guidelines identified overweight as a BMI of 25 to 29.9 and obesity as a BMI of 30 and above, which is consistent with the definitions used in many other countries, and supports the Dietary Guidelines for Americans issued in 1995. BMI describes body weight relative to height and is strongly correlated with total body fat content in adults. According to the guidelines, a BMI of 30 is about 30 pounds overweight and is equivalent to 221 pounds in a 6' person and to 186 pounds in someone who is 5'6". The BMI numbers apply to both men and women. Some very muscular people may have a high BMI without health risks.

The panel recommends that BMI be determined in all adults. People of normal weight should have their BMI reassessed in 2 years.

"The evidence is solid that the risk for various cardiovascular and other diseases rises significantly when someone's BMI is over 25 and that risk of death increases as the body mass index reaches and surpasses 30," said Dr. F. Xavier Pi Sunyer, chairman of the expert panel and director of the Obesity Research Center, St. Luke's/Roosevelt Hospital Center in New York City.

"The guidelines tell the truth about the risks associated with unhealthy weight. We hope that physicians and the public will take the message seriously and use the guidelines to begin to deal effectively with a difficult problem," asserted Dr. Pi-Sunyer.

According to a new analysis of the National Health and Nutrition Examination Survey (NHANES III), as BMI levels rise, average blood pressure and total cholesterol levels increase and average HDL or good cholesterol levels decrease. Men in the highest obesity category have more than twice the risk of hypertension, high blood cholesterol, or both compared to men of normal weight. Women in the highest obesity category have four times the risk of either or both of these risk factors.

The guidelines recommend weight loss to lower high blood pressure, to lower high total cholesterol and to raise low levels of HDL or good cholesterol, and to lower elevated blood glucose in overweight persons with two or more risk factors and in obese persons. Overweight patients without risk factors should prevent further weight gain, advise the guidelines.

In addition to measuring BMI, health care professionals should evaluate a patient's risk factors, such as elevations in blood pressure or blood cholesterol, or family history of obesity-related disease. At a given level of overweight or obesity, patients with additional risk factors are considered to be at higher risk for health problems, requiring more intensive therapy and modification of any risk factors.

Physicians are also advised to determine waist circumference, which is strongly associated with abdominal fat. Excess abdominal fat is an independent predictor of disease risk. A waist circumference of over 40 inches in men and over 35 inches in women signifies increased risk in those who have a BMI of 25 to 34.9.

According to the guidelines, the most successful strategies for weight loss include calorie reduction, increased physical activity, and behavior therapy designed to improve eating and physical activity habits. Other recommendations include:

• Patients should engage in moderate physical activity, progressing to 30 minutes or more on most or preferably all days of the week.

• Reducing dietary fat alone--without reducing calories--will not produce weight loss. Cutting back on dietary fat can help reduce calories and is heart-healthy.

• The initial goal of treatment should be to reduce body weight by about 10 percent from baseline, an amount that reduces obesity-related risk factors. With success, and if warranted, further weight loss can be attempted.

• A reasonable time line for a 10 percent reduction in body weight is six months of treatment, with a weight loss of 1 to 2 pounds per week.

• Weight-maintenance should be a priority after the first 6 months of weight-loss therapy.

• Physicians should have their patients try lifestyle therapy for at least 6 months before embarking on physician-prescribed drug therapy. Weight loss drugs approved by the FDA for long-term use may be tried as part of a comprehensive weight loss program that includes dietary therapy and physical activity in carefully selected patients (BMI >30 without additional risk factors, BMI >27 with two or more risk factors) who have been unable to lose weight or maintain weight loss with conventional nondrug therapies. Drug therapy may also be used during the weight maintenance phase of treatment. However, drug safety and effectiveness beyond one year of total treatment have not been established.

• Weight loss surgery is an option for carefully selected patients with clinically severe obesity -- BMI of > 40 or BMI of >35 with coexisting conditions when less invasive methods have failed and the patient is at high risk for obesity-associated illness. Lifelong medical surveillance after surgery is a necessity.

• Overweight and obese patients who do not wish to lose weight, or are otherwise not candidates for weight loss treatment, should be counseled on strategies to avoid further weight gain.

• Age alone should not preclude weight loss treatment in older adults. A careful evaluation of potential risks and benefits in the individual patient should guide management.

According to NHANES III, the trend in the prevalence of overweight and obesity is upward. The guidelines note that from 1960 to 1994, the prevalence of obesity in adults (BMI >30) increased from nearly 13 percent to 22.5 percent of the U.S. population, with most of the increase occurring in the 1990s.

"There are several possible reasons for the increase," asserted Karen Donato, coordinator of the Obesity Education Initiative. "When people read labels, they're more likely to notice what's lowfat and healthy' but may not be looking at calories. Also, more people are eating out and portion sizes have increased. Another issue is decreased physical activity. So people are consuming more calories and are less active. It doesn't take much to tip the energy balance," she said.

The upward trend in adult obesity has also been observed in children, notes the report. Since treatment issues surrounding overweight children and adolescents are quite different from the treatment of adults, the panel called for a separate guideline for youth as soon as possible. However, a healthy eating plan and increased physical activity is an important goal for all family members.

With that in mind, the guidelines contain practical information on healthy eating. Based on this material, the NHLBI has developed consumer tips on shopping, eating, and dining out.

The guidelines have been reviewed by 115 health experts at major medical and professional societies. They have been endorsed by the coordinating committees of the National Cholesterol Education Program and the National High Blood Pressure Education Program, the North American Association for the Study of Obesity, the NIDDK Task force on the Prevention and Treatment of Obesity, and the American Heart Association. These groups represent 54 professional societies, government agencies, and consumer organizations. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults will be distributed to primary care physicians in the U.S. as well as to other interested health care practitioners. It is available on the NHLBI Website. Single free copies of the consumer tips referred to above are available by writing to the NHLBI Information Center, P.O. Box 30105, Bethesda, MD 20824-0105.