We call for the veterinary profession to adopt uniform nomenclature for canine and feline obesity. There is currently no universally-accepted definition of obesity in dogs and cats, and this lack of professional consensus has created confusion among veterinary professionals, industry stakeholders, and owners. This makes it challenging for veterinarians to provide clear messages to their clients about obesity and might explain why veterinarians rarely record the presence of obesity in the clinical records of their patients.¹ We believe that adopting and widely publicizing a standard definition of obesity will raise awareness of the disease, and increase discussion and motivation to act within the profession with the ultimate goal of improving health of cats and dogs.

Our recommendation is that the term obesity be defined as 30% above ideal body weight. While excess body weight (overweight and obesity) represents a continuum and any cut-point for onset of disease is somewhat arbitrary (see below), this definition correlates with the determination of obesity in humans using the standard metric such as body mass index (BMI) and abdominal circumference.² It is also consistent and broadly supported by veterinary studies where there are associations with various comorbid diseases,^3-5 functional impairment,^6-11 and decreased quality of life.^12,13 The most practical clinical measure of adiposity is body condition score (BCS, see below), and 30% above ideal weight is equivalent to 8/9 using the preferred 9-point system.^14-17 However, defining obesity on the basis of ‘above ideal weight’, rather than on the basis of condition score, is preferable because it enables veterinarians to use other strategies to identify the onset of obesity precisely in addition to definition by BCS. For example, if a veterinary practice recommends routine body weight and BCS assessment throughout life, and such practices formally identifying and record the ‘healthy adult weight’ of a dog or cat (i.e. an early-adult-life bodyweight where BCS is ideal),¹⁸ weight gain could then be accurately quantified as a percentage change from the healthy adult weight, enabling the onset of obesity to be accurately determined.

We urge the global veterinary community to adopt a universal Body Condition Score for dogs and cats of whole-integer, one-through-nine (1–9) scale. Many different body condition scoring systems have been suggested for estimating the adiposity of dogs and cats^{3,4,14-17,19-22} and, while they may be broadly comparable (for example a 5-unit system using half units is broadly equivalent to a 9-unit system), having different methods creates confusion. Not only is this problematic for veterinary professionals and owners when discussing obesity and health care recommendations, it can also lead to inconsistency in interpreting the results of scientific studies.

In adopting a universal system, we believe that the 9-unit body condition score is preferable. This system has been more extensively validated than other systems, for example by comparing scores against precise measures of body fat mass using dual-energy X-ray absorptiometry, DEXA).^14-17,22 It is also the system that has been recommended by the WSAVA Global Nutrition Panel.²³ We recognize that other validated methods of determining adiposity have been developed for cats and dogs, such as using multiple zoometric measures.^20,21 While we would not discourage their use, we believe that body condition scoring has many advantages most notably speed and simplicity, to ensure consistent use in veterinary practices. By adopting a universal BCS, we believe veterinary teams will be better able to interpret veterinary medical research, more consistently and accurately assess their patients’ body condition, and clearly communicate with colleagues and clients.

We call for the veterinary profession formally to recognize canine and feline obesity as a disease. For many years, the medical profession has debated the various reasons for and against defining human obesity as a disease.^24-28 Opponents have argued that body fat gain is simply a normal physiological response to an abnormal (‘obesogenic’) environment.^27,28 However, obesity develops in a pattern expected for any disease process in that one or more causal factors trigger various pathophysiological mechanisms, which ultimately lead to functional impairment.²⁶ With obesity, the prolonged positive energy balance leads to expansion of adipose tissue and fat deposition in other organs; this in turn promotes dysregulation of metabolic, hormonal and/or inflammatory processes, ultimately leading to functional impairment, comorbidities of obesity and reduced quality of life. Obesity also meets the American Medical Association (AMA) definition of disease namely:

1. An impairment of the normal functioning of some aspect of the body
2. Demonstrates characteristic signs or symptoms
3. Causes harm or morbidity

The final arguments against classifying obesity as a disease are that the label would negatively impact well-being and would not improve medical support for affected individuals.^27,28 However, such arguments have been refuted by others who believe a formal obesity classification will actually reduce stigma and, in turn, improve access to medical care.^25,26 While a clear consensus has not yet been reached, the broad trend has been toward adopting a formal disease definition. This has been the position of the AMA since 2013,²⁵ and is now held by many other national medical organizations, the World Health Organization, World Obesity Federation, Food and Drug Administration and the National Institute of Health.^26,30,31

Obesity is now a major health concern worldwide with published studies suggesting that up to 59% of dogs and cats are overweight,^3,4,32 making obesity one of the most common medical disorders identified in veterinary practice.^5,34 Recent evidence suggests a rapidly increasing prevalence³⁵ and the fact that it is now a worldwide problem including developing countries.³⁶ Particularly concerning is the current prevalence of obesity in growing animals, whereby approximately 21% of dogs are already overweight by 6 months of age.³⁷ Obesity can reduce life expectancy,³⁸ negatively impact quality of life,^12,13 and is associated with various comorbidities.^3,4 Obesity contributes to metabolic derangements,^9-11,39 significant functional impairment (most notably respiratory, cardiovascular and renal function)^10,11 and is a significant financial burden on owners.⁴⁰ Thus, as with the condition in humans, the wealth of scientific data in cats and dogs to support the formal classification of obesity as a disease, and this is consistent with a position statement articulated by a group of international experts convened by the WSAVA One Health Committee.⁴¹ Obesity is further complicated by the fact that companion animals are unable to make diet and feeding choices, eliminating the complicating factor of personal accountability. By defining canine and feline obesity as a disease, regardless of exact cause, we believe both veterinarians and owners will be compelled to act. We also believe the designation as a disease will encourage the veterinary medical profession and industry to become more innovative and create solutions for this prevalent, yet often-neglected condition.

Some have argued against obesity being classified as a disease on the basis that diagnostic criteria (such as BMI in humans and BCS in animals) are imprecise and flawed.²⁷ They further argue that there is inconsistency in terms of when consequences of obesity are observed, such that two individuals with a similar degree of adiposity can have marked differences in comorbidities and overall health. They argue that obesity is instead a continuum and that applying an arbitrary definition of a disease state on top of this is unhelpful.²⁷ While we agree both that there are flaws in methodology used to quantify fat mass and that consequences are unpredictable, we disagree that these issues invalidate the classification of obesity as a disease.

Applying defined cut-points to a continuum is common across many chronic veterinary diseases, for example chronic kidney disease, where the staging of the International Renal Interest Society⁴² has received widespread acceptance. However, while the different stages are clearly demarcated by diagnostic cut-points based upon serum creatinine concentration, the presence of clinical consequences such as hypertension, proteinuria and uremic syndrome are inconsistent and variable. Similarly, the American College of Veterinary Dentistry has defined and described a disease classification system for the highly prevalent periodontal disease where the stages of periodontitis and furcation involvement of disease can vary between individual teeth of the same patient.⁴³ Further, flaws in diagnosis do not invalidate the ability of many other veterinary conditions to be called diseases. For example, despite admirable attempts at standardization,^44,45 the definition of inflammatory bowel disease remains unclear, and there is substantial inconsistency in interpretation among pathologists.⁴⁶ Therefore, to be consistent with other chronic diseases with similar characteristics, we call on global veterinary medical organizations and governing bodies to join us in the formal classification of canine and feline obesity as a disease.