Obesity Diagnostics

According to the World Health Organization (WHO), obesity is defined as “abnormal or excessive fat accumulation that presents a risk to health”.¹ In contrast to the view that obesity only represents a risk factor for diseases, the World Obesity Federation declared obesity itself as a chronic relapsing progressive disease.²

In current guidelines, diagnosis of obesity and treatment decisions are based on a body mass index (BMI) ≥30kg/m², despite the inability of BMI to accurately predict cardiometabolic risk or to define total and central abdominal fat mass.³ At any given BMI, the variation in comorbidities and health risk factors is remarkably high.³

Obesity may be considered a consequence of the interaction of different disease-causing factors. Such obesogenic factors include biologic (e.g. age, sex, genetics), society (e.g. work place, mode of transportation), behavior modifying (e.g. family, eating culture, friends) and environmental factors (e.g. availability and accessibility of energy-rich food, low requirements for physical activity).⁴ Many of these obesogenic factors cannot be actively changed which supports the view obesity is a disease not a decision. Together they can promote weight gain and maintain higher BMI even against targeted weight-loss attempts. Defining obesity as a disease would have a strong impact both on the individual in terms of improving self-esteem and reducing stigma, and on wider society in terms of increasing awareness amongst both health care professionals and politicians.

Health care professionals initially ask people with obesity about root causes and lifestyle factors (Figure 1) that may have led to development of unhealthy body weight and there will be a physical examination including measurements and blood tests.

Assessment of family and health history. Because obesity is considered a heritable disease, people with obesity will be asked about the body weight of parents, siblings and other relatives. There will also be a review of body weight history, weight-loss attempts and success, physical activity and exercise habits, eating patterns, satiety and appetite control, medications, stress levels, sleep and work patterns.

Physical examination. In addition to measurements of body weight, height, waist and hip circumferences, heart rate, blood pressure and body temperature are checked and the heart, lungs, abdomen and joints are examined. With the weight and height data, the BMI can be calculated to formally establish the obesity diagnosis and to stratify treatment.

BMI should be checked at least once a year to determine overall health risks, define treatment goals and inform strategies for weight loss.

Central fat distribution - which is associated with increased risk of cardio-metabolic disease- can be estimated by the waist circumference. For women, a waist circumference of more than 88 cm and for men more than 102 cm increases this risk. Based on these physical examination, further tests, such as ultrasound or an electrocardiogram may be recommended.

Body composition. A higher BMI can be misleading if people have large muscle mass. Therefore, body composition - fat, muscle and water components, are assessed by bioimpedance analyses or dual X-ray absorptiometry measurements. These analyses may provide important guidance for types of weight loss intervention because it is a more important treatment goal to reduce fat mass rather than total body mass.

Blood tests. Blood tests should be performed at the first visit to check for endocrine disorders that may cause obesity including hypothyroidism and hypercortisolism.  In addition, blood tests are required to diagnose other obesity-related diseases or risk factors, therefore parameters of lipid and glucose metabolism, chronic inflammatory states as well as kidney and liver function tests should be performed.

In some people, obesity may not cause any health impairments whereas in others it may cause metabolic issues (e.g. type 2 diabetes, dyslipidemia, fatty liver disease), cardiovascular diseases (e.g. hypertension, myocardial infarction, stroke), osteoarthritis, back pain, asthma, depression, cognitive impairment and even some types of cancer (e.g. breast, ovarian, prostate, liver, kidney, colon).⁴

BMI and waist circumference do not always reflect adverse obesity-associated health outcomes and the Edmonton Obesity Staging System (EOSS) has been developed as a five-stage system of obesity classification that takes account of metabolic, physical and psychological impairments (Figure 2). This system is intended to address the need for a more individualized definition of obesity and improve treatment decisions.⁵

Careful obesity diagnostics are the most important prerequisite to determine whether and how much weight a person with obesity should lose and what health conditions or risks are already present. Obesity diagnostics should identify individual predominant obesity causes and guide treatment decisions.