Version July 2025
INTRODUCTION —
The morbidity and mortality associated with being considered overweight or having obesity have been known to the medical profession for more than 2000 years [1]. According to the World Health Organization (WHO), obesity is defined as "excess or abnormal fat accumulation that presents a risk to health" [2]. The Centers for Disease Control and Prevention (CDC) defines it as "weight that is considered higher than what is considered healthy for a given height is described as overweight or obesity" [3]. Although it is an imperfect measure, both use body mass index (BMI) to further define these terms, with a BMI of 25 to 29.9 kg/m2 considered overweight and ≥30 kg/m2 as obesity. However defined (by WHO, CDC, or other), obesity is a chronic disease that is increasing in prevalence in adults, adolescents, and children and is now considered to be a global epidemic. Screening for obesity can identify high-risk patients who may not otherwise receive counseling about health risks, lifestyle changes, obesity treatment options, and risk factor reduction. Evaluation of a patient who is considered overweight or who has obesity should include both clinical and laboratory studies; the combined information is used to characterize the type and severity of obesity, determine health risk, and provide a basis for selecting therapy.
The prevalence of obesity, the approach to screening, and the clinical evaluation of obesity in adults will be reviewed here. The health risks associated with obesity and approach to treatment are discussed in detail separately. (See "Overweight and obesity in adults: Health consequences" and "Obesity in adults: Overview of management".)
PREVALENCE —
Obesity has been recognized as a major health issue in resource-abundant settings for more than three decades. With a surge in global prevalence, obesity has become a greater contributor to disability-adjusted life-years and death than undernutrition in more than 200 countries around the world [4].
United States — Estimates of the prevalence of obesity in the United States using consistent, standardized methods have been ongoing since 1960 [5,6]. Prevalence data have been collected in two ways: annual telephone surveys conducted by state Departments of Health in collaboration with the Centers for Disease Control and Prevention (the Behavioral Risk Factor Surveillance System [BRFSS]), and directly measured height and weight obtained in field surveys by the National Center for Health Statistics as the National Health and Nutrition Examination Survey (NHANES).
Data from BRFSS consistently report obesity prevalence rates lower than those found in the NHANES surveys. This is due to self-report bias (eg, people under-reporting their weight, over-reporting their height, or both) during telephone surveys. Thus, it is essential to identify the data source when evaluating obesity prevalence information.
Based upon data collected for NHANES from 1988 to 1994, 1999 to 2000, and 2021 to 2023, the age-adjusted overall prevalence of obesity in the United States increased progressively from 22.9 to 30.5 to 40.3 percent (figure 1) [7]. In 2021 to 2023, the prevalence of obesity was similar in adult males and females [8].
The age-adjusted prevalence of class III obesity (body mass index ≥40 kg/m2), sometimes referred to as severe obesity, has risen from 5.7 to 9.2 percent between 2007 and 2020 [7,9].
In 2022, the self-reported prevalence of obesity in United States adults ranged from 25 percent in Colorado to 41 percent in West Virginia [10]. The prevalence of self-reported obesity was generally higher in the Midwest and the South than in the Northeast and the West. Although the regional prevalence of self-reported obesity generally parallels the results obtained by more objective surveys, the reported degree of obesity is lower [11-13].
Projections using extrapolated data from BRFSS and NHANES suggest that by 2030, almost half of all United States adults will have obesity, and almost one-fourth will have severe obesity [14]. Another analysis estimated that by 2050, over 80 percent of adults will be considered overweight and over 55 percent will have obesity [15].
Canada — The prevalence of obesity is rising in Canada. In 1985, fewer than 10 percent of people in nine of the provinces had obesity; by 1990, this was true for only three of the provinces. By 1994, five provinces had obesity rates between 15 to 19 percent [16]. By 2016, more than 22 percent of males and 20 percent of females in all of Canada had obesity, a steady increase [17,18].
Global — In 2015, roughly 604 million adults had obesity worldwide, and the prevalence of obesity was higher for females than males across all socioeconomic levels and age groups [19]. From 1990 to 2022, the age-standardized prevalence of obesity increased in 90 percent of countries worldwide, including increases by more than 20 percentage points among females in 25 percent of countries and among males in 12 percent of countries (figure 2) [20]. Forecasts estimate that by 2050, 3.8 billion adults worldwide will be considered overweight or obese, with 1.95 billion having obesity [21].
SCREENING
Our approach — We suggest screening all adult patients for overweight and obesity by measuring body mass index (BMI) as part of their routine physical examination. We also recommend obtaining an additional anthropometric measure (eg, waist circumference) in those with BMI between 25 and 40 kg/m2. The additional measure is used to confirm excess adiposity in those with a BMI between 30 and 40 kg/m2, and it can help identify abdominal adiposity (and associated risk) in individuals with a BMI between 25 and 29.9 kg/m2 who may not otherwise be captured by BMI alone. (See 'Waist circumference' below.)
This is consistent with guidelines and expert opinion for the screening and evaluation of overweight and obesity [22-30].
Rationale — Obesity is associated with a significant increase in morbidity (including diabetes mellitus, hypertension, dyslipidemia, heart disease, stroke, sleep apnea, and cancer) and mortality. Weight loss is associated with a reduction in obesity-associated morbidity. (See "Overweight and obesity in adults: Health consequences" and "Obesity in adults: Overview of management", section on 'Importance of weight loss'.)
Without screening, many high-risk patients may not receive counseling about health risks, lifestyle changes, obesity treatment options, and risk factor reduction.
Clinicians miss opportunities to screen, diagnose, and manage obesity. As an example, in a study of 20,383 adults with BMI ≥25 kg/m2 seen in 57 primary care practices, only 12 percent received enough care for their weight that the clinician used a weight-related International Classification of Diseases, 10th Revision code for billing. Only 6 percent received more than lifestyle advice (ie, prescription of antiobesity medication or referral to a dietitian or specialist) [31]. Similarly, a 2018 report of 3008 patients with obesity found that only 55 percent had a diagnosis of obesity and even fewer had an obesity management plan documented by their clinicians [32].
Barriers to screening — A frequently cited barrier to screening is the potential risk of stigma associated with a diagnosis of obesity. Use of sensitive language around obesity (such as "unhealthy" or "excess" weight) and education about the increasing number of treatment options can improve patient engagement in their care. Using language such as "person with obesity" rather than "obese person" emphasizes that obesity is a disease and may reduce stigma.
Measurements
Body mass index — Measuring BMI is the generally accepted first step to determine the degree of overweight. The BMI is easy to measure, reliable, and correlated with percentage of body fat and body fat mass [33]. BMI provides a better estimate of total body fat compared with body weight alone [34].
Clinicians should be aware that BMI may overestimate the degree of adiposity in individuals considered overweight but very muscular (for example, professional athletes or bodybuilders) and underestimate it in older persons due to loss of muscle mass associated with aging. In addition, among older adults in whom there is a loss of height (eg, due to osteoporosis, kyphosis), we use the patient's current, measured height to calculate the BMI [35]. Although failing to consider height loss may suggest an artifactually high calculated BMI, there is typically an associated loss of muscle mass (and weight) with aging such that the calculated BMI reflects the degree of true adiposity.
Measurement of an additional anthropometric measure (eg, waist circumference) in conjunction with BMI can provide additional information on risk. (See 'Additional anthropometric measures' below.)
Calculation — The BMI is the most practical first step for evaluating the degree of excess weight. It is calculated from the weight and square of the height as follows:
BMI = Body weight (in kg) ÷ height (in meters) squared
The BMI can also be obtained from a calculator (calculator 1).
BMI-based classifications — Body mass index (BMI) classifications are based upon risk of cardiovascular disease [36]. The recommended classifications for BMI adopted by the National Institutes of Health (NIH) and World Health Organization (WHO) [22,37,38] for White, Hispanic, and Black individuals are (table 1):
●Underweight – <18.5 kg/m2
●Normal weight – ≥18.5 to 24.9 kg/m2
●Overweight – ≥25.0 to 29.9 kg/m2
●Obesity – ≥30 kg/m2
•Class I – 30.0 to 34.9 kg/m2
•Class II – 35.0 to 39.9 kg/m2
•Class III – ≥40 kg/m2 (also referred to as severe or extreme obesity)
These cutoffs underestimate the risk associated with obesity, such as diabetes, in the Asian population. The recommended BMI classifications adopted by the NIH and WHO for Asian individuals define overweight as a BMI of ≥23 to 24.9 kg/m2 and obesity as a BMI of ≥25 kg/m2.
Studies consistently demonstrate that the level of obesity-related risk at a given BMI is higher in Asian populations compared with White populations [39-42]. As an example, in a random sample of 1078 Canadian adults, the mean BMI associated with development of an adverse metabolic profile (defined by markers of glucose and lipid metabolism) was 21 kg/m2 among South Asian individuals and 30 kg/m2 among White individuals [40].
Additional anthropometric measures — We suggest obtaining an additional anthropometric measure in patients with a BMI between 25 and 40 kg/m2. This helps confirm excess adiposity in those with a BMI between 30 and 40 kg/m2 and helps identify abdominal adiposity in those with a BMI between 25 and 29.9 kg/m2. These measurements are not necessary in patients with BMI >40 kg/m2, as almost all individuals with this BMI are already at a high risk from their adiposity and further confirmation is not necessary.
Measurement of abdominal obesity and provides independent risk information that is not accounted for by BMI [43]. Patients with abdominal obesity (also called central adiposity, visceral, android, or male-type obesity) are at increased risk for heart disease, diabetes, hypertension, dyslipidemia, and metabolic dysfunction-associated steatotic liver disease [44-48] and have higher overall mortality rates [43,49-51].
Abdominal obesity can be measured as waist circumference, waist-to-hip ratio, or waist-to-height ratio. We generally use waist circumference, as it is the simplest of these to measure and has been best studied, although any of these is acceptable.
Waist circumference — A waist circumference of ≥40 in (102 cm) for males and ≥35 in (88 cm) for females is considered elevated and indicative of increased cardiometabolic risk [23].
The waist circumference is measured with a flexible tape placed on a horizontal plane at the level of the iliac crest as seen from the anterior view (figure 3). There is population variability in waist circumference values that predict increased risk. As an example, Japanese Americans and Indians from South Asia have more total fat and visceral fat and therefore may be at higher risk of developing type 2 diabetes for a given BMI than White individuals [39,52]. A waist circumference ≥31 in (80 cm) in Asian females and ≥35 in (90 cm) in Asian males is considered abnormal.
Waist-to-hip ratio — A waist-to-hip ratio is the circumference of the waist divided by the circumference of the hips (measured at the widest point). A ratio of ≥0.90 in males or ≥0.85 in females indicates an increased metabolic risk [53].
Waist-to-height ratio — A waist-to-height ratio is an alternative measure of central obesity can be calculated by as waist circumference divided by body height. It is interpreted as follows [54]:
●Healthy central adiposity (no increased health risks): 0.4 to 0.49
●Increased central adiposity (increased health risks): 0.5 to 0.59
●High central adiposity (further increased health risks): 0.6 or higher
A ratio >0.5 confirms excess adiposity associated with health risks [30].
Other measures (not routinely used) — Although dual-energy x-ray absorptiometry (DXA), computed tomography (CT), and magnetic resonance imaging (MRI) provide a more direct measurement than waist circumference for assessing the distribution of body fat, they are costly examinations and are generally reserved for use as research tools. We do not routinely use this in clinical practice.
In addition, body roundness index (BRI) is a new anthropometric measure that incorporates height and waist circumference to account for abdominal adiposity in predicting obesity-related risks. A cohort study of nearly 33,000 United States patients found that higher BRI is associated with all-cause mortality compared with average BRI [55]. However, the additional value of BRI beyond BMI and traditional anthropometric measures has not been established, and the measure has not been incorporated into routine clinical practice.
EVALUATION OF PATIENTS WITH OBESITY —
In patients considered overweight (body mass index [BMI] ≥25 kg/m2) or who have abdominal obesity (waist circumference ≥35 in [88 cm] in females or ≥40 in [102 cm] in males, waist-to-hip ratio ≥0.90 in males or ≥0.85 in females, or waist-to-height ratio >0.5), assessment of health risk may be warranted. This assessment may include a history, physical examination, and measurement of fasting glucose (or glycated hemoglobin [A1C]), thyroid-stimulating hormone, liver enzymes, and fasting lipids (figure 4). Results of the assessment should be shared with the patient and followed by a mutually agreed upon treatment or non-treatment plan. (See "Obesity in adults: Etiologies and risk factors".)
Investigating the cause — Many factors contribute to the development of obesity (table 2). Genetics are believed to account for over 50 percent of obesity. Although monogenic syndromes of obesity occur, obesity typically involves a polygenic process that is a complex interplay of genetic and environmental factors. Specifically, increasing sedentary behavior and excess caloric intake in the context of permissive genetics favor the development of obesity.
Although secondary causes of obesity are uncommon, they should be considered and ruled out [48].
To determine etiology and plan future management strategies, additional medical history should include age at onset of weight gain, events associated with weight gain, previous weight loss attempts, change in dietary patterns, history of exercise, current and past medications, and history of smoking cessation. Medications are a common cause of weight gain, in particular insulin, sulfonylureas, thiazolidinediones, glucocorticoids, and antipsychotics (table 3). Smoking cessation is also associated with weight gain. (See "Benefits and consequences of smoking cessation", section on 'Weight gain'.)
Females have more body fat as a percent of body weight than males from puberty onward and tend to gain more fat during adult life than males. In addition, females may experience modest but adverse increases in body weight and fat distribution after a first pregnancy that persist. (See "Overview of the postpartum period: Disorders and complications", section on 'Postpartum weight retention'.)
Findings from physical examination that might point to a secondary or related cause of obesity include goiter (hypothyroidism); proximal muscle weakness, moon facies, and/or purple striae (Cushing's syndrome); and acne and/or hirsutism (polycystic ovary syndrome [PCOS]). (See "Obesity in adults: Etiologies and risk factors".)
Additional testing may be required depending upon the findings on history, physical examination, and initial blood tests. This could include laboratory tests to assess the hypothalamic-pituitary axis if there are signs of disorders such as Cushing's syndrome, growth hormone deficiency, or hypothalamic obesity. (See "Obesity in adults: Etiologies and risk factors", section on 'Conditions associated with weight gain'.)
Routine genetic testing is not recommended, as monogenic disorders that include obesity are rare and usually present in childhood. Measurement of metabolic rate is not recommended, as it is not widely available and may be misinterpreted. (See "Obesity: Genetic contribution and pathophysiology", section on 'Heritable factors'.)
Preclinical versus clinical obesity — We stratify patients with obesity based on whether excess adiposity is causing any organ or tissue damage, or affecting daily function. Patients with "clinical obesity" have health effects related to their weight, whereas those with "preclinical obesity" do not have apparent effects related to extra weight [30]. This stratification can help guide counseling and treatment decisions.
●Clinical obesity – The diagnosis of clinical obesity can be made in patients who meet measurement-based criteria for obesity and have any obesity-related health condition, organ dysfunction, or symptom.
Common obesity-related conditions include:
•Cardiovascular conditions including hypertension, heart failure, atherosclerotic disease, chronic or recurrent atrial fibrillation, and pulmonary artery hypertension.
•Endocrine conditions including insulin resistance or type 2 diabetes, metabolic syndrome, polycystic ovarian syndrome, and male hypogonadism
•Obstructive sleep apnea
•Metabolic-associated steatotic liver disease
Common obesity-related symptoms include:
•Urinary incontinence
•Knee or hip pain
•Breathlessness or wheezing
•Limitations in mobility or other basic activities of daily living (eg, bathing, dressing)
These criteria are not comprehensive; the diagnosis of clinical obesity can be made based on any symptom or condition which is thought to be related to weight and does not have an alternate etiology. Our guidance is similar to that of other experts [30].
●Preclinical obesity – Preclinical obesity is defined as excess adipose tissue, but without any of the above-described conditions or symptoms due to extra weight. In patients without current health effects related to weight, we evaluate for risk factors that predict future obesity-related health effects (ie, future risk of clinical obesity).
Factors that may increase the risk of developing clinical obesity include:
•Degree of overweight (BMI)
•Presence of abdominal obesity (eg, elevated waist circumference)
•Additional cardiovascular risk factors (eg, dyslipidemia, cigarette smoking)
•History of childhood obesity. Individuals who have had longstanding obesity have a greater risk of obesity-related morbidity (including diabetes and hypertension) and mortality. [56,57] (See "Definition, epidemiology, and etiology of obesity in children and adolescents".)
•Weight gain after age 18 years. Even very modest weight gain (≥5 kg) after age 18 years in females and after age 20 years in males increases the risk of CHD and type 2 diabetes at all levels of initial BMI [56].
Candidates for weight-loss interventions — Because of known health risks associated with excess body weight [36], people with BMI ≥25 kg/m2 are candidates for weight-loss interventions. We individualize interventions based on overall health status and risk factors for obesity-related morbidity and mortality, as well as patient goals and preferences. The goal of therapy is to prevent, treat, or reverse the complications of obesity, including decrements in quality of life. (See "Obesity in adults: Overview of management".)
●Low risk – Patients with BMI between 25 and 29.9 kg/m2 without an additional anthropometric measure of adiposity and without symptoms or signs of obesity are at low risk for future obesity-related morbidity. We provide counseling regarding prevention of further weight gain, including advice on dietary habits and physical activity. (See "Obesity in adults: Role of physical activity and exercise", section on 'Exercise to prevent weight gain'.)
●Moderate risk – For moderate-risk patients, we provide counseling about weight-loss interventions, emphasizing diet, physical activity, and behavioral modifications. Medications may be appropriate for some individuals. This group generally includes:
•Patients with BMI between 25 and 29.9 kg/m2 who have an additional anthropometric measure of adiposity, and/or symptoms or signs of obesity
•BMI ≥30 kg/m2 without an additional anthropometric measure of adiposity and without signs or symptoms of obesity
•Patients with BMI ≥30 kg/m2 with an additional anthropometric measure of adiposity, but without symptoms or signs of obesity (ie, preclinical obesity)
●High risk – Patients with clinical obesity (BMI ≥30 kg/m2 who have an additional anthropometric measure of adiposity and symptoms or signs of obesity), are at high risk for obesity-related morbidity and mortality. We offer intensive management for obesity, including diet, physical activity, behavioral modification, and discussion of medications. Surgery may be appropriate in some individuals.
This is a general framework to help guide treatment decisions. Management of individuals may vary based on severity of weight-related conditions, patient preferences, and other individual factors. There are few data to support specific targets, and this approach is based on clinical experience and expert opinion.
Specific recommendations for the treatment of obesity are reviewed separately. (See "Obesity in adults: Overview of management" and "Obesity in adults: Dietary therapy" and "Obesity in adults: Drug therapy" and "Obesity in adults: Behavioral therapy".)
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Obesity in adults".)
INFORMATION FOR PATIENTS —
UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Weight loss treatments (The Basics)")
●Beyond the Basics topics (see "Patient education: Losing weight (Beyond the Basics)" and "Patient education: Weight loss surgery and procedures (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Screening – We suggest that all adult patients be screened for overweight and obesity (Grade 2B). This is done by measuring body mass index (BMI) (calculator 1) at the routine physical examination. In addition, we suggest obtaining an additional anthropometric measure (eg, waist circumference) in those with BMI between 25 and 40 kg/m2 (Grade 2C) as abdominal adiposity (and associated risk) may not be captured in this BMI range. Additional measurements are unnecessary in patients with BMI >40 kg/m2. (See 'Our approach' above.)
●Measurement of obesity
•Body mass index – BMI classifications are based upon risk of cardiometabolic disease (table 1). The classification is used for identifying adults at increased risk for morbidity and mortality due to obesity. However, the relationship between percent body fat and BMI is different among different patient populations. In White, Hispanic, and Black individuals, overweight is defined as a BMI of 25 to 29.9 kg/m2 and obesity as a BMI of ≥30 kg/m2. In Asian individuals, overweight is defined as a BMI of ≥23 to 24.9 kg/m2 and obesity as a BMI of >25 kg/m2. (See 'BMI-based classifications' above.)
•Additional anthropometric measures – Waist circumference, waist-to-hip-ratio, and waist-to-height ratio, are measurements of abdominal obesity and provide independent risk information that is not accounted for by BMI. Patients with abdominal obesity (also called central adiposity, visceral, android, or male-type obesity) have an increased risk for overall mortality, heart disease, diabetes, hypertension, dyslipidemia, and metabolic dysfunction-associated steatotic liver disease. (See 'Additional anthropometric measures' above and 'Waist circumference' above.)
●Evaluation
•Whom to evaluate – In individuals with BMI ≥25 kg/m2 or abdominal obesity (waist circumference ≥35 in [88 cm] in females or ≥40 in [102 cm] in males, waist-to-hip ratio ≥0.90 in males or ≥0.85 in females, or waist-to-height ratio >0.5) we suggest further evaluation to assess overall risk status (figure 4) (Grade 2B).
•Components of evaluation – The evaluation includes a history, physical examination, and measurement of fasting glucose (or glycated hemoglobin [A1C]), thyroid-stimulating hormone, liver enzymes, and fasting lipids (figure 4).
•Potential causes – Many factors contribute to the development of obesity (table 2). Obesity typically arises from a complex interplay of genetic and environmental factors, including sedentary lifestyle and increased caloric intake. Although secondary causes of obesity are uncommon, they should be considered and ruled out, typically with history and physical examination. (See 'Investigating the cause' above.)
•Preclinical versus clinical obesity – We evaluate a patient's current health status to determine whether they have any obesity-related symptoms or conditions (eg, type 2 diabetes, obstructive sleep apnea, heart failure). Those who do are classified as having clinical obesity, whereas those who have no health effects related to weight have preclinical obesity. We also assess additional risk factors for future obesity-related morbidity, including degree of overweight (BMI), presence of abdominal obesity (waist circumference), additional risk factors for cardiovascular disease (eg, smoking or hyperlipidemia), and weight history. (See 'Preclinical versus clinical obesity' above.) Subsequent intervention is based upon overall risk assessment. (See 'Evaluation of patients with obesity' above.)
●Intervention
•All individuals who would benefit from weight loss should receive counseling on diet, physical activity, behavioral modification, and goals for weight loss. Individuals who do not need to lose weight can be counseled regarding prevention of weight gain. The relationship between BMI and risk allows identification of several levels that can be used to guide further selection of therapy. (See 'Candidates for weight-loss interventions' above.)
•Specific recommendations for the treatment of obesity are reviewed separately. (See "Obesity in adults: Overview of management" and "Obesity in adults: Dietary therapy" and "Obesity in adults: Drug therapy" and "Obesity in adults: Behavioral therapy".)
ACKNOWLEDGMENT —
The UpToDate editorial staff acknowledges George Bray, MD, who contributed to an earlier version of this topic review.
