Obesity is a complex and multifactorial disease that is influenced by physiological, psychological, environmental, socio-economic and genetic factors.¹ ²
Click on each factor above to find out more.
BMI=the weight in kilograms divided by the square of the height in metres (kg/m2).7
≥18.5 and <25.0
≥25.0 and <30.0
Obesity, class I
≥30.0 and <35.0
Obesity, class II
≥35.0 and <40.0
Obesity, class III
Waist circumference can be used alongside BMI to assess a person’s risk for developing obesity-related complications. A larger waist circumference is associated with an increased risk of developing obesity-related complications and mortality.2
|Waist circumference cut-offs to identify increased relative risk for the development of obesity-related complications:2|
>102 cm (>40 in)
>88 cm (>35 in)
European Association for the Study of Obesity (EASO)
“A progressive disease, impacting severely on individuals and society alike, it is widely acknowledged that obesity is the gateway to many other disease areas.”12
The Obesity Society (TOS)
It is the official position of The Obesity Society that obesity should be declared a disease.8
American Medical Association (AMA)
"Recognizing obesity as a disease will help change the way medical community tackles this complex issue that affects approximately one in three Americans."9
American Association of Clinical Endocrinologists (AACE)
"...obesity is a primary disease, and the full force of our medical knowledge should be brought to bear on the prevention and treatment of obesity as a primary disease entitity."10
World Obesity Federation (WOF)
The World Obesity Federation takes the position that obesity is a chronic, relapsing, progressive disease process and emphasises the need for intermediate action and the prevention and control of this global epidemic.11
Despite the recognition of obesity as a disease by many professional medical bodies, the ACTION Study has shown that 45% of people with obesity have not yet received a formal diagnosis of obesity.13
Obesity is now so prevalent that it is one of the most significant contributors to ill health, replacing traditional public health concerns, such as undernutrition and infectious disease.7 An integrated approach, requiring actions from all sectors of society, will be necessary to achieve effective prevention and management of obesity.7
The global prevalence of obesity has nearly tripled since 1975. In 2016, more than 1.9 billion adults aged ≥18 were overweight. Of these, 13% had obesity.15
The global economic impact of treating obesity and its related complications amounts to $800 billion per year and it is expected to reach $1.2 trillion by 2025.24
The cost of obesity is comparable to other non-communicable diseases, such as cardiovascular disease for which the global cost will reach $1 trillion by 2030.25
Scientific literature states that a weight loss of 5% or more can help to improve and reduce the risk of some obesity-related complications.26-28,31-34 People with obesity (84%) and healthcare professionals (88%) agree that a 10% weight loss is beneficial to overall health.13
Research shows that a high BMI is associated with a decreased life expectancy of up to 10 years.35
For every 5 kg/m2 BMI increment above the range of 22.5–25.0 kg/m2, there is a 30% increase in overall mortality.*35
Adapted from Prospective Studies Collaboration. Body-mass index and cause-specific mortality in 900,000 adults: collaborative analyses of 57 prospective studies. Lancet. 2009;373(9669):1083–1096.
‡Data from male subjects.
People with obesity have a 55% increased risk of developing depression over time, whereas people with depression have a 58% increased risk of developing obesity.36
Several studies have found that the effect of weight stigma on people with obesity may lead to depression and a lower health-related quality of life.36
Cardiovascular disease is the leading cause of mortality in people with obesity.21
BP=blood pressure; CV=cardiovascular; DBP=diastolic blood pressure; HbA1c=glycated haemoglobin; HDL=high density lipoprotein; SBP=systolic blood pressure.
A weight loss of around 7% has shown a reduction in the incidence of type 2 diabetes by 58%26
Every 1 kg of weight loss can increase HDL levels by 0.009 mmol/L23
Achieving ≥5% weight loss can lead to an 80% risk reduction of sleep apnoea progression30
The higher the BMI, the greater the risk of impaired physical functioning, which may include limitations in mobility activities such as walking and dressing.37,38
Physiological responses to weight loss favour weight regain.4,39-42
Weight loss alters the body's homeostatic system,43 which controls appetite, energy intake and energy expenditure,44 causing the body to increase hunger and lower the metabolic rate.43
Want to learn more about the science behind obesity? View our obesity mode of disease video.
Weight loss in people with obesity causes changes in appetite hormones that increase hunger and the desire to eat for at least 1 year.4
A review of 14 long-term studies showed that people with obesity regained weight after weight loss achieved by dieting.45
“…the high rate of relapse among people with obesity who have lost weight has a strong physiological basis and is not simply the result of the voluntary resumption of old habits.”4
Study participants’ weight and diet statuses were assessed at baseline; their weight was then monitored for up to seven years after the diet ended. These data are from a review of 14 diet studies with long-term follow-ups.45
Adapted from Mann T, Tomiyama AJ, Westling E, Lew AM, Samuels B, Chatman J. Medicare's search for effective obesity treatments: diets are not the answer. Am Psychol. 2007;622(3):220–233.
People with obesity engage in several serious weight loss attempts; however, only 10% were able to maintain the achieved weight loss for more than one year.13
Obesity should be treated holistically and as a serious chronic disease.10,47
Only 55% of people with obesity report being diagnosed with obesity. Among those who have discussed weight with their healthcare professional, only 24% reported that a weight-related follow-up appointment was scheduled.13
Evidence-based lifestyle therapy for obesity should include diet, exercise and behavioural modification.47 Healthy eating, physical activity and behaviour therapy should be first-line interventions in all individuals with a BMI ≥25 kg/m2 and they must be part of any weight-loss intervention.47 However, these interventions are not always sufficient to maintain weight loss.45,48
Pharmacotherapy for obesity can be considered if lifestyle therapy does not provide sufficient clinical benefit for individuals with a BMI of ≥30 kg/m2, or ≥27 kg/m2 with obesity-related complications.48 Anti-obesity medications can act directly on the central nervous system, inducing weight loss by reducing appetite, or act peripherally and induce weight loss by interfering with absorption from the gastrointestinal tract.49
Bariatric procedures are the third-line intervention for obesity management, which is recommended in individuals with a BMI ≥40 kg/m2, or ≥35 kg/m2 with comorbidities. Bariatric surgery can be malabsorptive or restrictive, with each type requiring different lifestyle changes.50
Clinical practice guidelines for comprehensive medical care of patients with obesity according to BMI stage.48
Click here to explore our patient interaction tools to aid initiation or follow-up of dialogue with patients about their obesity management.
Explore the science behind obesity interactive infographic to learn more about the factors inside and outside the body that affect a person’s likelihood of developing obesity.