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Obesity Guidelines Development Methodology

The panel has attempted to provide primary care practitioners with recommendations regarding effective strategies to evaluate and treat overweight and obesity in adults. The panel anticipates that the recommendations also will be followed by the large proprietary weight loss industry in the United States. The guideline is based on a systematic review of the scientific literature published in MEDLINE from January 1980 through September 1997. This was done in the interest of time and economy. This information was supplemented by material provided by the panel and a search of appropriate references in eligible articles. The panel identified randomized controlled trials as the strongest level of evidence for the evaluation of treatment efficacy. Thus, evidence from randomized controlled trials (RCTs) serves as the basis for many of the recommendations contained in this guideline. However, in some instances, the panel had to make recommendations in the absence of RCTs. Each evidence statement (other than those with no available evidence) and each recommendation is categorized by level of evidence (A through D). Statements for which there is no available evidence are so indicated.

Panel Selection

The National Heart, Lung, and Blood Institute (NHLBI) Obesity Education Initiative Task Force recommended panel members representing the various expertise required to deal with the issues of cardiovascular disease and body weight. The executive director of the American Academy of Family Physicians (AAFP) also provided recommendations for the primary care practitioner who would represent AAFP. The panel members include primary care practitioners, clinicians from academic medical centers, nutritionists, exercise physiologists, pulmonologists, cardiologists, psychologists, behaviorists, epidemiologists, and experts on cost issues. Some of the panel members were also members of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) National Task Force on the Prevention and Treatment of Obesity. The funding source for the guidelines was primarily the NHLBI, with the cooperation of the NIDDK of the National Institutes of Health.

Topics Included in the Guidelines

The panel decided to focus on all adult (18 years of age and older) overweight and obese patients with a body mass index (BMI) ≥ 25, and particularly those with cardiovascular risk factors. Excluded from the analysis were patients with known genetic or hormonal syndromes and pharmacologically induced obesity.

In addition, since pediatric obesity contributes to about one-third of adult obesity, the panel felt that some attention needed to be focused on the issue of overweight in children and adolescents. Treatment issues surrounding overweight children and adolescents are quite different from the treatment of adults. The panel recommended that this issue warrants its own project as soon as possible.

The therapeutic interventions requiring examination included diet, physical activity, behavior therapy, pharmacological therapy, surgery, and combinations of these. No clinical interventions were excluded at the outset. Because of the importance and complexity of the primary prevention of obesity, the panel decided not to deal with these concerns in detail and that the issue be addressed in a separate document. However, clinical interventions to prevent further weight gain in patients already overweight, or those patients not currently overweight at high risk for becoming overweight, were considered relevant therapeutic interventions. The guideline also contains some information on the cost of obesity.

In terms of reliable diagnostic measures, the panel decided to concentrate on useful tools readily available in a physician's office, i.e., weight, height and BMI. The panel did not search for evidence to prove that measures of body composition or metabolic rate are useful tools; however, they did include studies using these diagnostic measures.

Development of the Evidence Model

The panel determined the evidence model used to develop the guidelines for the evaluation and treatment of obesity. The model contains two broad categories, the association of weight to cardiovascular and noncardiovascular mortality and morbidity in the population and the clinical issues related to the treatment of the overweight individual. The population portion of the model addresses such questions as, "Is there an association between weight and cardiovascular risk factors?", and "Is there an association between weight and cardiovascular and noncardiovascular morbidity and mortality?" The patient portion of the model focuses on the clinical setting and addresses such questions as, "Does a reduction in weight result in a decrease in cardiovascular morbidity and mortality?"

Search and Review of the Literature

The literature was searched and systematically reviewed by

  • establishing a priori eligibility criteria for inclusion of studies;
  • reviewing titles and abstracts to select promising articles;
  • reviewing these full articles; and
  • compiling evidence tables summarizing those articles that met the inclusion criteria.

The panel decided on the parameters for the literature search, particularly for the search dealing with the model linking treatment to weight loss. The parameters of the search included year of publication, country, language, study design, length of the study, outcome measures (which, what, and when), and patient characteristics (age and weight).

The panel decided to limit its search to English-language studies, but included foreign studies that provide an English abstract and are randomized controlled clinical trials. The search included human studies only published in MEDLINE from January 1980 to September 1997. No editorials, letters, or case reports were accepted. The panel was aware that two books published in the early 1980s coded the bulk of the obesity literature written to that point.

Panel staff and librarians at the National Library of Medicine's National Information Center for Health Services Research determined the medical subject heading terms used in the literature review.

Of the 43,627 titles acquired from the MEDLINE search, 18,217 were duplicates, leaving 25,410 titles to be considered. Using the ProCite reference database, the 25,410 titles were screened by two reviewers and ultimately marked for their appropriateness. Abstracts for the appropriate 8,040 remaining titles were then screened for relevance in two rounds. Two individuals independently reviewed each abstract using the inclusion and exclusion criteria developed by the panel. A third reviewer would sporadically check the quality of the screening. This review led to 2,440 possibly relevant abstracts. Due to the greater quality of the evidence, the decision was made that randomized controlled trials pertinent to the treatment portion of the model be the top priority for data abstraction. Ultimately, 394 articles of randomized controlled trials were reviewed for data abstraction.

Literature Abstraction and Preparation of Evidence Tables

In order to abstract the correct data related to the treatment portion of the model in a consistent manner, a 25-page form called the "Critical Review Status Sheet (CRSS)" was developed. The CRSS was reviewed and approved by the panel. It took into account the inclusion and exclusion criteria described below and allowed for (1) the collection of data on the study's purpose and design; (2) the intervention parameters, including the format, setting, practitioners, population demographics, and detailed descriptions of the intervention per se, be it dietary, physical activity, behavioral, pharmacotherapy, or other types of interventions (surgery, acupuncture, hypnosis, etc.); and (3) outcome measures, including the method of determining the outcome, and adverse events. The CRSS was pilot-tested by staff as well as by staff of the San Antonio Cochrane Center.

The San Antonio Cochrane Center is one of 12 centers around the world that comprise the Cochrane Collaboration. The Cochrane Collaboration is an international organization established in 1993 whose mission is to prepare, maintain, and disseminate systematic reviews and meta-analysis of health care interventions. The San Antonio Center provides advice on multiple aspects of systematic review, including searching and selecting materials, abstracting materials, organizing materials into evidence tables, and performing meta-analysis.

Inclusion and exclusion criteria—The appropriateness of an article was determined by applying criteria determined by the panel. These criteria included the time frame for the study, i.e., the minimum amount of time that must pass before the outcome measure is made; how body weight was reported; and the type and size of the study. In defining the time frame, the panel needed to clarify if the important outcome was weight loss or sustained weight loss. Due to the importance of both outcomes, the panel decided to include studies that considered the effects during the acute phase of weight loss, and those that examined effects during the maintenance phase. Both types of studies were deemed important, and two cutpoints were considered appropriate for follow-up. At a minimum, studies had to have a time frame from start to finish of at least 4 months. However, in order to consider the question of long-term maintenance, studies with outcome data provided at approximately 1 year or longer were examined. The panel decided to exclude studies that used only self-reported weights for their measurement. No exclusion of studies was made by study size.

Preparation of evidence tables-Of the 394 articles of randomized controlled trials considered for data abstraction by the San Antonio Cochrane Center, 158 were rejected for a variety of reasons; i.e., randomization was not adequate or subjects were not all overweight or obese. Ultimately, 236 articles were abstracted by two separate reviewers who independently read and abstracted each article according to the CRSS. The reviewers met, compared coding, and resolved discrepancies. The data were then compiled into individual evidence tables developed for each RCT. In addition, summary tables were developed to compile the evidence necessary to address the 23 questions relevant to the treatment portion of the model.

The Formulation of the Evidence into the Guidelines

In order to consider the evidence for each of the 23 questions, the panel met in groups of 6 to 10 members. During the first round of considering the evidence, 12 small groups of panel members were randomly assigned to consider the evidence for 2 or 3 questions. They developed evidence statements and determined the strength of the evidence. Their recommendations were presented to the full panel, which then made additional recommendations regarding their conclusions.

After considering additional studies for questions where adequate RCTs were not available, another iteration of evidence statements and recommendations was developed. The full panel met again to consider this iteration, which was considered by small groups assigned to focus on either a specific treatment modality or outcome measure. The small groups brought their recommendations back to the full panel for their final consideration. The panel weighed the evidence based on a thorough examination of the threshold or magnitude of the treatment effect.


Each evidence statement (other than those with no available evidence) and each recommendation is categorized by a level of certainty (A through D) as described below. The consensus process used for drawing conclusions and writing the recommendations was a group process that took into account all opinions. Conclusions reflect the widest possible agreement of the panel.

Evidence Categories

Evidence Category Sources of Evidence Definition
A Randomized controlled trials (rich body of data) Evidence is from endpoints of well-designed RCTs (or trials that depart only minimally from randomization) that provide a consistent pattern of findings in the population for which the recommendation is made. Category A therefore requires substantial numbers of studies involving substantial numbers of participants.
B Randomized controlled trials (limited body of data) Evidence is from endpoints of intervention studies that include only a limited number of RCTs, post hoc or subgroup analysis of RCTs, or meta-analysis of RCTs. In general, Category B pertains when few randomized trials exist, they are small in size, and the trial results are somewhat inconsistent, or the trials were undertaken in a population that differs from the target population of the recommendation.
C Nonrandomized trials Observational studies Evidence is from outcomes of uncontrolled or nonrandomized trials or from observational studies.
D Panel Consensus Judgment Expert judgment is based on the panel's synthesis of evidence from experimental research described in the literature and/or derived from the consensus of panel members based on clinical experience or knowledge that does not meet the above-listed criteria. This category is used only in cases where the provision of some guidance was deemed valuable but an adequately compelling clinical literature addressing the subject of the recommendation was deemed insufficient to justify placement in one of the other categories (A through C).

Consideration of Special Populations and Situations

The panel also evaluated population factors and clinical situations that might potentially influence the physiological, medical, behavioral, or sociocultural context for obesity identification and treatment. Evidence on special populations and situations was captured from non-RCT evidence when available, but in many cases such evidence was meager. Population factors selected for special consideration with respect to obesity classification and treatment were age, gender, race/ethnicity, socioeconomic status, pregnancy, eating disorders, sleep apnea, extreme obesity, concurrent treatment of other major conditions (such as heart disease or diabetes), and treatment of obesity in conjunction with smoking cessation.

These considerations were addressed in all stages of guideline development. Persons with relevant special expertise were invited to serve on the panel. The search for evidence was formulated to ascertain studies that include special populations. Studies evaluated were coded to permit analysis of the extent to which the special populations or situations of interest had been included and whether findings for these populations and situations deviated from those for the majority populations in these studies. In the numerous cases where evidence on these special issues was insufficient to meet standards for inclusion in the main text of the guideline, potentially important issues were identified for the user and cross-referenced to an appendix or discussed in sidebar text.

External Review of the Guidelines

The external review of the guidelines included 115 reviewers from 59 government agencies, professional societies, and consumer groups represented on the Coordinating Committees of the National Cholesterol Education Program and the National High Blood Pressure Education Program, as well as the NIDDK's National Task Force on the Prevention and Treatment of Obesity, and selected members of the North American Association for the Study of Obesity.

Reviewers were asked to evaluate the guideline based on five criteria: validity, clarity, flexibility, completeness, and clinical applicability. Reviewers were also encouraged to provide additional comments. Comments of the peer reviewers were evaluated by the panel and panel staff, and were incorporated into the guideline where appropriate.

Caveats to Recommendation Use

In applying these guideline recommendations, the reader should note some caveats:

  • The emphasis of these guidelines was to identify effective interventions, not to rank-order interventions in terms of relative efficacy or effectiveness. The panel chose not to emphasize comparisons among interventions, because there were few studies that compared long-term outcomes, and, since patient preference often dictates choice of therapy, we wished to present a menu of options rather than a ranked list of choices.

  • When no evidence was available on the efficacy of various treatments, the panel usually rendered no opinion. An absence of studies should not be confused with an absence of effect. While clinicians may wish to use proven therapies in preference to untested therapies, the lack of testing does not prove that the untested therapy does not work.

  • The limitations of RCTs must be kept in mind. The RCT is the primary method for demonstrating efficacy. Often, patients enrolled in RCTs differ from the patients in a primary care practice, and effectiveness in the community may differ from efficacy as measured in an RCT. The potential exists for misinterpretation of clinical trial results. Analysis of endpoints not specified at the outset, post hoc, or subgroup analyses should be viewed as hypothesis-generating rather than hypothesis-testing.

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Obesity Guidelines Full Report

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The Practical Guide

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