• Obesity is a chronic, progressive and relapsing disease, characterized by the presence of abnormal or excess adiposity that impairs health and social well-being.
• Screening for obesity should be performed regularly by mea­suring body mass index (BMI) and waist circumference.
• The clinical assessment of obesity should aim to establish the diagnosis and identify the causes and consequences of abnormal or excess adiposity on a patient’s physical, mental and functional health.
• Providers participating in the assessment of obesity should focus on establishing values and goals of treatment, identi­fying which resources and tools may be needed and foster­ing self-efficacy with the patient in order to achieve long-term success.
• A non-judgmental, stigma-free environment is necessary for an effective assessment of a patient living with obesity.

1. We suggest that healthcare providers involved in screening, assessing and managing people living with obesity use the 5As framework to initiate the discussion by asking for their permission and assessing their readiness to initiate treatment (Level 4, Grade D, Consensus).
2. Healthcare providers can measure height, weight and calculate Body Mass Index (BMI) in all adults (Level 2a, Grade B),^1–9 and measure waist circumference in individuals with a BMI 25–35 kg/m² (Level 2b, Grade B).^10–12
3. We suggest a comprehensive history to identify root causes of weight gain as well as complications of obesity and potential barriers to treatment be included in the assessment (Level 4, Grade D).^13–15
4. We recommend blood pressure measurement in both arms, fasting glucose or glycated hemoglobin and lipid profile to determine cardiometabolic risk and, where appropriate, ALT to screen for nonalcoholic fatty liver disease in people living with obesity (Level 3, Grade D).^16,17
5. We suggest providers consider using the Edmonton Obesity Staging System to determine the severity of obesity and to guide clinical decision making (Level 4, Grade D).^18,19

• Obesity is a chronic disease characterized by the accumu­lation of excess body fat that can have a negative impact on your physical and mental health, as well as your overall quality of life.
• To guide you and your clinician on the best obesity treat­ment options, a clinical evaluation is needed to determine how your weight impacts your health and wellbeing. This may include both a mental health assessment and a physical exam.
• Weight bias and stigma are common in the setting and can be detrimental to helping you achieve your health goals. Healthcare providers should conduct their obesity assessment in a sensitive and non-judgmental way.

Introduction

Obesity is a chronic disease that requires a systematic and com­prehensive diagnosis, assessment and treatment approach.²⁰ The objective of an obesity assessment is to gather information to confirm the diagnosis, determine the severity of the disease and related comorbidities, identify triggers and drivers, and to guide appropriate management discussions in a non-biased and stig­ma-free clinical setting.²¹ Providers should initiate a discussion with the patient about their values and goals for treatment, fa­cilitate reflection and encourage accountability and self-directed management to promote long-term improvements in health.¹⁵

This chapter provides an evidence-based approach to assessing obesity in the primary care setting through a structured history, physical exam and clinically appropriate laboratory testing. The authors also discuss clinical tools that allow for easy and efficient use in routine clinical practice.

Definition of obesity

Obesity is a prevalent, complex, progressive and relapsing chronic disease characterized by abnormal or excessive body fat (adiposity) that impairs health.^22–24 Obesity has traditionally been viewed as a risk factor for a wide range of other health issues. The Cana­dian Medical Association,²⁰ however now considers obesity to be a chronic disease in its own right, similar to type 2 diabetes, hypertension and dyslipidemia (in line with other organizations including Obesity Canada, the American Medical Association,²⁵ the World Health Organization,²⁴ the World Obesity Federation and others).^25–27

Initiating a discussion about obesity management

Primary care providers play an important role in the management of most chronic diseases. However, due to the multitude of demands in primary care and lack of comfort and training, the assessment and management of obesity is not easily undertaken. The initial ap­proach, communication and attitude of the physician during an obesity assessment is a significant determinant to the patient’s success.^28,29

Many patients living with obesity have experienced some form of weight bias in the setting.^30,31 This is due in part to profession­als’ endorsement of negative attitudes and beliefs about obesity, misinformation about causality and perceptions that patients with obesity may be unmotivated and noncompliant. Many patients feel discriminated against, and, as a result, will often avoid seek­ing treatment and delay preventive care.³² This can affect their health status, their relationship with professionals and their re­sponse to interventions.³³

We recommend that healthcare providers approach patients with empathy and sensitivity. In addition, it’s important to acknowl­edge the complexity of the disease and the difficulty in sustaining behavioural change as well as avoid stereotypes and oversimplifi­cation of the disease.³⁴ A supportive environment with appropri­ate equipment (for example, appropriately sized blood pressure cuffs and gowns, armless chairs in waiting rooms, a private room for weigh-ins) and asking for permission to weigh patients can help foster patient comfort and dignity. Stigmatization of patients leads to worsened outcomes and promotes disordered eating, in­creased rates of depression and lower rates of physical activity.³⁵ This is reviewed in detail in the chapter Reducing Weight Bias in Obesity Management, Practice and Policy.

The use of structured interview formats (such as Obesity Canada’s 5As of Obesity ManagementTM) has been proposed to help facili­tate discussions about obesity in primary care.^36,37 An adaptation of the 5As’ template has been developed by Obesity Canada for use in clinical practice. The main components of this framework include:

1. ASKING for permission to discuss weight and explore readiness;
2. ASSESSING obesity-related risks and root causes of obesity;
3. ADVISING on health risks and treatment options;
4. AGREEING on health outcomes and behavioural goals; and
5. ASSISTING in accessing appropriate resources and providers.^38,39

Finally, when conducting an obesity assessment and in order to achieve long-term success, it is important to assess each patient’s readiness to change, intrinsic motivation and value and goals when initiating a treatment plan.⁴⁰ Personalizing the approach, recognizing patients’ strengths and reframing misconceptions about obesity are important key processes that can have a posi­tive impact on the patient’s ability to make long-term changes.^15,24 These concepts are reviewed in detail in the Effective Psychological and Behavioural Interventions in Obesity Management chapter.

Screening for obesity

Prior to initiating screening or assessment for obesity, it is important to ask patients’ permission to discuss the topic and/or to conduct anthropometric measurements. Evaluation of anthropometric pa­rameters is recommended as a practical screening tool to iden­tify patients with increased adiposity in whom more intensive assessments may be indicated.⁴¹ Moreover, performing regular anthropometric screening can identify patients at risk of develop­ing obesity in whom awareness of their risk and implementation of preventive measures can have a significant positive long-term effect on their health.^42,43 Many anthropometric parameters have been recommended in the screening and assessment of obesity;, however, a calculated body mass index (BMI) and measured waist circumference (WC)⁴⁴ are the most widely used.

Traditionally, BMI (weight [kg]/height² [m]) has been used as a sur­rogate measure of body fat, and thus an objective parameter to define obesity, both in epidemiological and clinical studies.^12,45–48 Large epidemiological studies have shown that Asian populations may have increased adiposity and cardiometabolic risk at a lower BMI, and alternative cut-off points have been proposed for this patient population.^49–54 Widely accepted classification of obesity based on specific BMI cut-offs are presented in Table 1.

For most populations, the presence of overweight (BMI ≥ 25 kg/m²) represents an increased risk and requires further evaluation of oth­er anthropometric, hemodynamic and biochemical parameters.^4,55 A BMI ≥ 30 kg/m² is associated with an increase in cardiovascular risk factors and all-cause mortality and should be used as a screen­ing criterion to identify obesity in the general population.^4,5 In adults with South-, Southeast- or East Asian ethnicity, the recom­mended BMI cut-off for overweight should be ≥ 23 kg/m². In spe­cial populations such as the elderly, very muscular patients, and those with extreme tall or short stature, the BMI can be misleading and needs to be interpreted with caution.⁹

Health Canada recommends the diagnosis of obesity not be based on BMI alone.⁵⁶ Nevertheless, given its simplicity, objectivity, and reproducibility, BMI continues to be an important measure in epi­demiological and population-based surveillance studies. In a clin­ical setting, BMI at the recommended cut-offs should serve only as a simple screening measure. When used together with other clinical indicators such as WC and clinical evaluation of cardiomet­abolic and other obesity related complications, BMI can help iden­tify individuals who may benefit from obesity management. WC has been independently associated to increase cardiovascular risk; however, it is not a good predictor of visceral adipose tissue on an individual basis.⁵⁷ Integration of both BMI and WC in clinical assessment may identify the higher-risk phenotype of obesity bet­ter than either BMI or WC alone, particularly in those individuals with lower BMI.^58–60

Regular assessment of BMI, WC and cardiometabolic risk factors can help identify people at greater risk of developing obesity. Reg­ular assessment should also inform care and allow for increased vigilance avoiding obesogenic medications (see Table 8) and coun­selling on the avoidance of weight gain during high risk time peri­ods, such as pregnancy or forced sedentariness due to injury (see Prevention and Harm Reduction of Obesity [Clinical Prevention]).

Table 1: Recommended Classification of BMI ^45,53

Although BMI is a simple, objective, and reproducible measure, it has certain limitations that need to be recognized by clinicians using these tools.^36,37

• BMI is not a direct measure of body fat, cardiovascular risk or health.
• BMI does not indicate body fat distribution.
• BMI does not account for muscle mass (it overestimates body fat in muscular individuals).
• BMI can underestimate body fat in people who have lost muscle mass (sarcopenic obesity).
• BMI does not distinguish between men, women or ethnicity.
• BMI is less accurate in certain populations (e.g. the elderly, people with physical disability, people <18 years of age, people with severe obesity, during pregnancy and in patients with ascites or severe edema).
• BMI over- or underestimates body fat in certain ethnic groups, such as Indigenous Peoples, South Asians, Chinese and other populations.

Waist circumference

Considering the limitation of BMI in determining fat composi­tion and distribution as well as the anatomical variations in fat deposition, the use of WC has been recommended as a surro­gate measure of abdominal or visceral fat.⁶¹ There is epidemio­logical evidence to suggest that WC can help identify individuals at increased risk for cardiometabolic disease.^57,62,63 A standardized method for accurately measuring WC is outlined in Box 2. Current recommended WC cut-offs are included in Table 2.

In the United States and Canada, a WC ≥ 102 cm (in men) or ≥ 88 cm (in women) indicates an increased risk of visceral adiposity and of developing cardiometabolic comorbidities. For adults with a predominant South Asian, Southeast Asian, or East Asian ethnicity, a lower cut-off for WC (≥ 85 cm in men and ≥ 75 cm in women) is recommended.

Despite its low-tech appeal and significant statistical association with cardiometabolic risk, there are important limitations to the routine use of WC measurement in the clinical setting:

• WC is not a direct measure of visceral fat.
• Considerable training and standardization are required to en­sure inter- and intra-reader reproducibility.
• WC is sensitive to abdominal distention due to food or fluid intake, bloating, ascites, pregnancy, etc.
• Varying cut-offs for ethnic populations.
• Less sensitive measure of visceral fat with increasing BMI.
• WC requires further body exposure and can be perceived as an intrusive measurement by some patients.

As with BMI, WC can be used as a simple and practical screening tool to identify individuals at higher risk of cardiometabolic disease. This may be particularly true for individuals who fall below the accepted BMI cut-offs for obesity. A variety of optimal cut-off values have been proposed, depending on ethnicity, measuring technique and outcomes of interest. Most cut-offs range from 65.5 to 101.2 cm for women and 72.5 to 103 cm for men.^63,69–71 Pa­tients with an increased BMI (< 35 kg/m2) and an elevated WC are associated with an increased risk of developing cardiometabolic risk factors such as diabetes mellitus type 2 and hypertension.⁷² Those with a BMI > 35 kg/m² are likely to be at an increased risk of cardiometabolic risk factors irrespective of their WC.

Integration of anthropometric measurements

Both BMI and WC provide valuable and complementary information in the assessment of obesity and the estimation of cardiometabolic risk. Among individuals with an elevated BMI (< 35 kg/m²), having an increased WC may imply a greater risk of developing significant cardiometabolic outcomes. Furthermore, among patients with a normal BMI, an increase in WC may imply intra-abdominal fat deposition and an increased risk of cardiometabolic disease.⁷³ These patients may benefit from early intervention to treat and prevent obesity-related complications. Finally, measuring WC in patients with a BMI > 35 kg/m² may not change management, but it can provide patients with valuable information regarding the efficacy of their treatment during their long-term follow-up. Some patients can see changes in adipose distribution before a significant change in body weight or BMI.

Table 2: Proposed Waist Circumference Cut-Off Points (cm) to Define Increase Abdominal Adiposity by Predominant Ethnicity

Assessing the impact of excess or abnormal adiposity on health

The association between the diagnosis of obesity and the devel­opment of obesity-related complications is strong but not always linear; therefore, comparable levels of excess adiposity obesity can have different levels of impact on health and quality of life for different patients. Similarly, multiple reports have documented a subgroup of “metabolically healthy” patients with obesity, char­acterized by the absence of any objective evidence of increased cardiometabolic risk despite having an elevated BMI and waist circumference.^74,75 Despite the absence of concurrent cardiometa­bolic risk factors, the so-called metabolically healthy patients with obesity should not be considered to be fully medically healthy, as these patients are at increased risk of mortality,⁷⁵ and are more likely to suffer other non-metabolic conditions associated with obesity such as sleep apnea, depression and joint/back pain, among others. Information gathered in the obesity assessment and analyzed using the Edmonton obesity staging system^18,19 can help to understand the severity of the disease and guide the inten­sity of treatment required.

Edmonton Obesity Staging System

Elements of the Edmonton Obesity Staging System (EOSS) have been proposed to guide clinical decisions from the obesity assess­ment and at each BMI category.¹⁹ Table 3 reviews the proposed clinical staging and its impact on management. EOSS is a measure of the mental, metabolic and physical impact that obesity has had on the patients’ health and uses these factors to determine their stage of obesity (from stage 0–4). In population studies, EOSS has been shown to be a better predictor of all-cause mortality when compared to BMI or waist circumference measurements alone.⁴⁰

Table 3: Edmonton Obesity Staging System

Once the diagnosis has been established, the primary goal for the clinical assessment for obesity should be to identify the possi­ble causes leading to weight gain, determine the extent to which weight has affected the patients’ health and to systematically look for barriers in their management.⁷⁶ Given that obesity is a complex and heterogeneous disease, this is often a daunting task for primary care providers. Using a clinical tool such as the 4Ms framework (Mental health, Mechanical, Metabolic, Monetary health / Milieu) can provide a practical approach for primary care physicians to explore major drivers, barriers and complications of obesity (see Table 4).⁷⁷ It can be used to provide a structure to perform an efficient and complete obesity assessment, including the history, physical exam and clinically indicated investigations.

Table 4: Components of the 4ms Framework for Assessment of Obesity ⁷⁷

Components of an obesity-centred history

An obesity-centred history should include all parts of a routine clinical interview, such as past medical and surgical history, med­ications, allergies and social and family history. However, an em­phasis should be placed on screening for underlying root causes and consequences of obesity (reviewed in Table 4). Key elements of the history include screening for sleep disorders, physical, sexual and psychological abuse, description of eating patterns, physical ac­tivity and screen time, internalized weight bias, mood and anxiety disorders, as well as substance abuse and addiction.^13,14 A thor­ough history of medications should screen for weight-promoting medications. Consider alternative options where possible. The most common weight-promoting medications are outlined in Ta­ble 8. The clinician conducting the assessment should also identify and document the patient’s values and goals around treatment and foster insight to help with long-term coping and self-man­agement skills.^15,24 Table 5 reviews some key components which are specific to an obesity-focused interview. Key processes of a personalized obesity assessment in primary care are highlighted in Table 5; these have been shown to have a positive impact on the patient’s’ ability to foster everyday change and facilitate improve­ments in their physical, mental and social health.^15,24

Components of an obesity-centered physical exam

An obesity-centered physical exam should be focused on de­termining the obesity phenotype, drivers of weight gain and treatment barriers for all patients. The key components of an obesity-centred physical exam are outlined in Table 6. Routine an­thropometric measurements should include height, weight, BMI and waist circumference. Blood pressure should be measured with an appropriately sized cuff according to the patient’s arm circum­ference. If a large upper arm size is prohibitive, systolic blood pres­sure can be measured in the forearm selecting the cuff size [small cuff (20.0–26.0 cm), standard cuff (25.4–40.6 and 25.0–34.0 cm) and large cuff [>32.0 cm]) according to participant’s forearm cir­cumference. For cuff installation in the forearm position the distal edge of the cuff should be located about 6 cm proximal to the styloid process of the ulna.^81,82 Neck circumference and airway patency are also helpful to estimate the risk of sleep apnea. In addition to a routine cardiorespiratory, a head, neck and gastrointestinal exam should be performed along with a general skin examination to rule out common skin findings (see Table 6). A joint and gait ex­amination is also recommended to assess for barriers in mobility. A cursory endocrine exam includes palpating for an enlarged thyroid gland and screening for signs of Cushing syndrome and polycystic ovarian syndrome. These signs, if present, should prompt further biochemical screening.

Investigations to assess obesity

Diagnostic testing is commonly ordered during the initial assess­ment of obesity to identify metabolic problems and to tailor therapy. There is no single blood test or diagnostic evaluation that is indicated for all patients with obesity. The specific evaluations performed should be based on the presenting symptoms, the patient’s risk factors and index of suspicion. Table 7 reviews some blood and di­agnostic testing for clinicians to consider when assessing a patient with obesity. Screening for metabolic syndrome with a HbA1c or fasting blood sugar, total cholesterol, serum triglycerides and HDL level is recommended in most patients.⁸⁴ Patients who are at high risk of fatty liver disease, including those with type 2 diabetes or metabolic syndrome, should be screened with an ALT level and an abdominal ultrasound. A referral to gastroenterology/hepatology may be appropriate in patients with persistently elevated liver en­zymes (greater than two times the upper limit of normal over six months and/or high FIB-4 scores). The gold standard to diagnose non-alcoholic fatty liver disease is a liver biopsy.⁸⁵

Evaluation of coronary artery disease

Large prospective studies have documented obesity as being an independent predictor of coronary artery disease.⁸⁶ This relation­ship was stronger in younger individuals. Susceptibility to obe­sity-related cardiovascular complications is not only mediated by overall body fat mass, but is largely dependent upon individual differences in regional body fat distribution.^73,87 Large cohort stud­ies using imaging techniques have identified excess abdominal vis­ceral adipose tissue as a strong predictor in the development of cardiovascular disease over time, independently of total body fat mass.⁸⁸ Numerous noninvasive tests can diagnose atherosclero­sis or myocardial ischemia, or both. The correct choice depends on local expertise, the relative strengths and weaknesses of each modality and individual patient characteristics, as well as pretest likelihood of coronary artery disease.

Electrocardiogram

Obesity has the potential to impact the ECG in several ways, in­cluding displacement of the heart by elevating the diaphragm in the supine position, increasing the cardiac workload and in­creasing the distance between the heart and the recording elec­trodes. Besides low QRS voltage and left-ward trend in the axis, other alterations frequently seen are nonspecific flattening of the T-waves in the infero-lateral leads (attributed to the horizontal dis­placement of the heart) and voltage criteria for left atrial abnor­mality. An increased incidence of false positive criteria for inferior myocardial infarction in individuals living with obesity, due to the elevation of the diaphragm has been reported.⁸⁹ Left ventricular hypertrophy is probably underdiagnosed based on the usual ECG criteria in individuals with greater than Class II obesity. Since base­line ECG may be influenced by obesity (false positive for inferior myocardial infarction, microvoltage, nonspecific ST-T changes) and patients with obesity may have impaired maximal exercise testing capacity (dyspnea, mechanical limitations, left ventricular diastolic dysfunction), other modalities may be of interest in the evaluation of coronary artery disease in this population. Indeed, due to impaired exercise tolerance because of mechanical and physiological limitations related to stress testing in patients at very high BMIs, a perfusion scan may be used instead of exercise test­ing for evaluating the presence of ischemic heart disease.

Table 5: Recommended Key Components of an Obesity-Centred Medical History

Table 6: Key Components of An Obesity-Centred Physical Exam

Exercise stress test

Standard stress test performance is limited in patients with obesity for a number of factors. ECG modification might limit accurate in­terpretation. Aerobic capacity is diminished because of pulmonary dysfunction, orthopaedic limitations and left ventricular diastolic dysfunction. Many patients with obesity fail to achieve 80–85% of the age-predicted heart rate needed for diagnostically valid re­sults.^90,91 Standard Bruce and modified ramp protocols achieve valid results in most patients, with patients terminating the test because of fatigue, leg pain or dyspnea.⁹² Patients with obesity may also experience mobility, joint and balance issues limiting their ability to use a treadmill. In these patients, the use of a bike ergometer is recommended. Higher systolic and diastolic blood pressures are typ­ically found during the exercise stress test in patients with obesity.⁹³

Nuclear imaging techniques

Technetium sestamibi is the marker of choice in patients with obesity because of greater energy emission, which generates better im­ages.^94–96 Weight-based limitations might occur in patients with a body weight above 350 pounds (~160 kg), which might require planar imaging. Newer and more sensitive cameras might eliminate some of these issues, but their use still leads to challenges with table weight and size, given that proper positioning of the patient is required in order to use this system. Positron emission tomog­raphy (PET) computed tomography rubidium has a 91% sensi­bility, 89% specificity, is faster than sestamibi-SPECT, produces less radiation exposure, better quality images and correction for attenuation, and has a greater degree of diagnostic precision and a reduced need for invasive examinations.⁹⁷ The PET rubidium is the nuclear imaging technique of choice for patients with obesity.

Stress echocardiography

Despite some limitations, exercise stress echocardiography is a valid technique for patients with obesity.⁹⁸ The feasibility of stress echo, us­ing either physiological stress (treadmill exercise) or pharmacological stress (dobutamine) is excellent in most cases. It is widely available, low-cost, radiation free and has no weight limits. Stress echocardiog­raphy is highly operator-dependent and can be limited in the pres­ence of poor acoustic windows related to pulmonary disease, obesity and respiratory motion. If severe limitations exist, transesophageal echocardiography with dobutamine might be useful.⁹⁹

Evaluation of other conditions associated with obesity

Women with obesity and symptoms of polycystic ovary syndrome should be screened for LH, FSH, total testosterone, DHEAS, prolactin, TSH and 17 hydroxyprogesterone levels. Other endocrinopathies, including thyroid dysfunction, Cushing’s’ or acromegaly are not routinely recommended unless clinically warranted. We encourage age-appropriate cancer screening for patients with obesity as they are at an increased risk and often have poor outcomes due to lower rates of routine screening and delays in seeking treatment.

Can you have a high BMI and be healthy?

As with most health indicators (e.g. blood pressure, blood glu­cose, cholesterol), there exists a curvilinear relationship between the amount of body fat and its impact on health. In epidemiolog­ical studies the relationship between body fat (or BMI as a surro­gate) and health impacts follows a U-shaped curve with health risks progressively increasing at both the lower and higher ends of the BMI spectrum.¹⁰⁰ While there is a statistically significant rela­tionship between increasing BMI and health risks, a given individ­ual can present with virtually no relevant health issues over a wide range of BMI levels.^101,102 Although individuals with an elevated BMI who appear healthy may have a modestly elevated health risk (and a high likelihood of developing complications in the long-term),¹⁰³ there is currently no evidence to support long-term benefits of intentional weight loss in these individuals. A prudent approach to individuals presenting with an elevated BMI without the presence of overt impairment to health, would be to reinforce health behaviours aimed at preventing further weight gain and reducing the development of relevant complications.

Table 7: Laboratory and Diagnostic Tests to Consider in the Assessment of Patients with Obesity

Table 8: Summary of Weight Promoting Medications and Alternate Therapies

i) Department of Medicine, University of Saskatchewan

ii) Department of Endocrinology and Metabolism, McMaster University

iii) Faculty of Health Sciences, Simon Fraser University

iv) Quebec Heart and Lung Institute, Université Laval

v) Department of Medicine, University of Alberta

A complete list of author’s competing interests can be found on the CMAJ website, HERE

Cite this Chapter

Rueda-Clausen CF, Poddar M, Lear SA, Poirier P, Sharma AM. Canadian Adult Obesity Clinical Practice Guidelines: Assessment of People Living with Obesity. Available from: https://obesitycanada.ca/guidelines/assessment. Accessed [date].

Update History

Version 1, August 4, 2020. The Canadian Adult Obesity Clinical Practice Guidelines are a living document, with only the latest chapters posted at obesitycanada.ca/guidelines.

The summary of the Canadian Adult Obesity Clinical Practice Guidelines is published in the Canadian Medical Association Journal, and contains information on the full methodology, management of authors’ competing interests, a brief overview of all recommendations and other details. More detailed guideline chapters are published on the Obesity Canada website at www.obesitycanada.ca/guidelines.