Reframing obesity in veterinary medicine

Introduction

Pet obesity is a common chronic health disorder of growing global concern. In a recent large-scale epidemiological study of veterinary clinics across North America, encompassing nearly 5 million dogs and over 1 million cats (1), the prevalence of overweight and obese body condition was 62.7% in dogs (50.1% overweight, 12.6% obese) and 66.5% in cats (44.8% overweight, 21.7% obese) (Figure 1). The study also highlighted that the prevalence of obesity increases with age, reaching its highest levels during the mature adult stage.

Recent shifts in perspective within both human and veterinary medicine have advanced the understanding of obesity and its clinical implications. This article will examine in greater depth the suggested reclassification of obesity and outline the benefits of this change, and discuss its role in clarifying the distribution of responsibilities within the veterinary team. Such a framework not only facilitates the development of individualized management strategies but also supports prioritization in cases where comorbidities increase clinical complexity.

Is obesity a disease?

There has been longstanding debate over whether or not obesity should be classified as a disease, both in humans and companion animals (2,3). Proponents would argue that obesity fulfills all criteria of a disease definition and classifying it as such could improve access to care; opponents would question the heterogeneity amongst patients (where two people or pets could have the same amount of body fat but its impact on health could differ markedly) and instead argue it is better considered to be a risk factor rather than a disease.

New classification

This debate was directly addressed by a recent Lancet Commission, comprising 58 international experts in obesity, which was initially convened in 2022 and reported in early 2025 (4). This review was commissioned to assist with clinical decision making and to guide prioritization of treatment interventions. The group comprehensively reviewed all existing evidence, came to consensus and published its findings (4). The commission defined obesity by the presence of excess adiposity with or without disruption to normal organ and body function or impact on daily living. Additionally, the commission recommended subdivision of obesity cases based on the health impact it was having; the suggestion was to classify obesity as either clinical or pre-clinical. The clinical category would include those where dysfunction was identified resulting in chronic systemic illness due to the excess of adipose tissue. The preclinical category recognized a state of obesity but where function for the most part was retained; however, these individuals were at high risk of developing clinical obesity.

Shortly after publication it was suggested that veterinary medicine take a similar approach (5). With similar, adapted parameters used for the definition of obesity, its classification and diagnosis, it recognizes that obesity could be thought of as a chronic disease (i.e., for clinical cases), and also not a disease as yet (i.e., in cases of preclinical obesity) and in so doing, bringing clarity to how obesity in pets is managed by the whole veterinary team.

Defining obesity in pets

In primary care veterinary practice, obesity is mainly identified using a combination of regular weighing and body condition scoring (BCS) (6). Although other, more precise methods are available, e.g., dual-energy x-ray absorptiometry (DEXA) (7), they are impractical for most veterinary professionals, making BCS the preferred primary care approach. When using the 9-point BCS system, a BCS ≥ 5/9 represents a degree of either overweight or obesity. Having a BCS of 6-7/9 and 8-9/9 is consistent with the phenotypes of overweight and obesity, respectively. Associated with this excess accumulation of adipose tissue are both direct and indirect adverse health consequences. Therefore, after identifying an obese phenotype, its nature should then be determined, in terms of whether it is preclinical or clinical. This distinction facilitates the development of tailored treatment strategies, the prioritization of therapeutic goals, and the allocation of responsibilities between the veterinarian and the veterinary nurse/technician, depending on the degree of clinical involvement required.

The differentiation between clinical and preclinical obesity relies upon physical examination findings, information from the owner about their pet (regarding the impact of obesity on daily living and quality of life) and, in some cases, diagnostic tests (e.g., routine hematology, serum biochemistry and urinalysis). Suggestions for possible adverse health impacts that were seen in cases with clinical obesity are shown in Table 1 (5). This classification is made by findings of an abnormal physical examination in conjunction with abnormalities in hematological and biochemical analysis.

 

Table 1. Direct adverse health effects associated with clinical obesity (from 5)

 

 

To determine whether obesity is exerting adverse effects on a cat or dog’s health, it is essential to supplement the physical examination with targeted questioning. Given that cats and dogs may appear clinically unaffected within the consulting room, additional information provided by owners regarding the pet’s behaviors and condition in the home environment is necessary to achieve a comprehensive assessment. In the authors’ experience, the questions in Box 1 are useful when making a diagnosis of clinical obesity.

 

Box 1. Questions for owners to determine the direct impact of obesity on their pet’s health.

 

 

Indirect health effects

The main indirect health effects resulting from obesity arise from the development of other diseases that arise at the same time as the obesity. Such diseases fall into three broad categories:

• Those which cause obesity (e.g., hypothyroidism, hyperadrenocorticism)
• Those where obesity is either a risk factor or an exacerbator (so-called “obesity-associated” diseases)
• Those that have arisen independently of the obesity (so-called “comorbidities”) but nevertheless need to be considered in management.

Such associated diseases, where obesity is either a risk factor for, or an exacerbator of, the conditions include: 

• Musculoskeletal diseases (8-10), e.g., osteoarthritis, cruciate ligament disease, hip dysplasia
• Cardiorespiratory diseases (11-16), e.g., tracheal collapse, altered cardiac function, poor ventilation and oxygenation
• Endocrine diseases (9,17), e.g., diabetes mellitus, hypothyroidism, hyperadrenocorticism
• Neoplasia (9)
• Lower urinary tract disease (10,18,19)
• Miscellaneous disease, e.g., poor skin and coat quality, oxidative stress, undesirable behaviors which may include food-related stealing or guarding (20), increased anesthetic risk.

Therefore, it is not uncommon for obesity to be present concurrently with other diseases that also need to be managed. Importantly, the presence of a comorbidity should not prohibit the provision of obesity care (Figure 2) and, given that direct and indirect health effects will differ amongst cases, an individualized approach is essential. In each case, judgement on what is having the biggest impact on the cat or dog should be made, although for the vast majority, therapeutic weight reduction can and should still be attempted, albeit with reasonable adjustments. Two case studies follow, which illustrate the approach to diagnosis and care of obesity.

Case 1. Jackson.

Signalment

• Breed: Alaskan Malamute x Chow Chow
• Sex: Male, neutered
• Age: 8 years old
• Starting weight: 58 kg
• Body condition score: 9/9

Presenting complaint

• Exercise intolerance, lethargy, snoring (Figure 3).

Clinical history review and physical findings

• Obesity, osteoarthritis, low serum thyroxine concentration.

Diagnosis

• Clinical obesity with concurrent hypothyroidism.

Key priorities

• Therapeutic weight reduction
• Replace thyroid hormone deficiency
• Improve mobility and exercise intolerance
• Improve quality of life
• Prevention of further obesity and additional adverse impacts to health

Outcome

• Final weight: 42 kg
• Weight lost kg: 16 kg
• Weight lost: 28%
• Duration of weight loss: 346 days (49 weeks)
• Average weight loss: 0.6% per week

Excellent weight-loss results were observed (Figure 4). In addition, Jackson’s lethargy resolved, whilst his activity and mobility level greatly improved. As a consequence, his quality of life increased significantly.

Comments on Jackson’s case

This case required input from both a veterinarian and veterinary nurse/technician. The diagnosis of both the obesity and hypothyroidism was made by the veterinarian, who prescribed levothyroxine as treatment for the latter. Once Jackson was stable, the nurse/technician was able to implement and monitor an obesity care plan, which involved feeding a purpose-formulated dry diet (ROYAL CANIN^® Satiety) suitable for therapeutic weight reduction. 

Hypothyroidism is frequently “blamed” for causing obesity in dogs; however, it is much rarer than is generally perceived by both pet owners and veterinary professionals, with < 1% of dogs presenting obesity also having concurrent hypothyroidism (9). That said, when hypothyroidism is diagnosed, replacement therapy is important (as an underactive thyroid makes weight loss challenging), and so drug therapy to replace the thyroid hormone will be required for successful management of the hypothyroidism. Further, whilst thyroid replacement therapy alone will promote some weight loss, a formal therapeutic weight reduction protocol must also be implemented to ensure that goals of obesity care are achieved. 

Case 2. Ruby.

Signalment

• Breed: Domestic shorthair
• Sex: Female, neutered
• Age: 9 years old
• Starting weight: 7.3 kg
• Body condition score: In excess of 9/9

Presenting complaint

• Obesity, reduced activity and mobility (Figure 5).

Clinical history review and physical findings

• In addition to the obesity, azotemia (both increased urea and creatinine concentration) was discovered on biochemical analysis. Additional assessments included urinalysis and indirect blood pressure measurement, enabling a diagnosis of early International Renal Interest Society (IRIS) stage 2 chronic kidney disease (CKD) (21).

Diagnosis

• Clinical obesity and a comorbidity (early IRIS stage 2 CKD).

Key priorities

• Weight reduction, minimize further renal compromise, maintain muscle mass, prevent further weight gain and associated health consequences, and improve quality of life.

Outcome

• Final weight: 5.6 kg
• Weight lost kg: 1.7 kg
• Weight lost: 23%
• Duration of weight loss: 209 days (30 weeks)
• Average weight loss: 0.8% per week

Excellent weight-loss results were observed (Figure 6). Mobility and activity level were reported to have greatly improved. Biochemical kidney parameters remained stable with no exacerbation or progression of the CKD.

Comments on Ruby’s case

This complex case required significant care from both a veterinarian and a veterinary nurse/technician for a successful outcome, most notably by ensuring that weight loss could occur safely, without progression of the CKD.

The diet chosen in this case was a purpose-formulated wet and dry diet (ROYAL CANIN^® Satiety) which is suitable for safe therapeutic weight reduction. A key feature of the chosen diet is the inclusion of an increased protein content, which is controversial; this is because higher protein diets almost invariably have more phosphorus and, therefore, would not typically be recommended for cats with CKD, where reducing phosphorus intake is typically recommended. However, what matters when feeding cats with early CKD is controlling total daily phosphorus intake; provided that the high-protein diet is only fed for weight reduction, this will not be problematic, because the reduced daily food intake will offset the increased phosphorus content of the diet. Of course, once the weight reduction phase has been completed, an appropriate diet for weight maintenance should then be selected, which might be a mildly (e.g., diet formulated for senior cats, IRIS stage 1-2, serum phosphate < 1.5 mmol/L) or moderately (e.g., therapeutic renal diet, IRIS stage 2, phosphate concentration > 1.5 mmol/L) phosphorus restricted diet, depending on the CKD stage and serum phosphate concentration.

Throughout the period of weight reduction, serum biochemical analysis was performed periodically to ensure that the CKD did not progress. The target weight in this case was also adjusted to ensure that adipose tissue loss was promoted, while lean tissue mass was preserved. Therefore, a partial weight reduction plan was chosen, with a loss of 20% being recommended as an initial target (compared to the 45% weight loss that would have been required to return the cat to a BCS of 5/9, a so-called “complete” weight reduction protocol). The rationale for this was that lean tissue loss during therapeutic weight reduction is proportional to the total percentage weight loss; whilst some lean tissue loss always occurs after substantial weight reduction (> 20%), lean tissue is largely preserved with more modest weight reduction (10-15%). A target of 20% was chosen for Ruby to provide balance between potential benefits and harms.

Conclusion

The classification of obesity in companion animals has long been debated, not least whether it should be considered to be a disease, and has arguably resulted in inconsistent treatment pathways and ambiguity over professional responsibilities. Recent advances in human medicine have proposed recognizing obesity as either clinical or preclinical depending on the degree of functional disruption caused by the excess adiposity, a model now being adapted for veterinary practice. In cats and dogs the degree of adiposity is primarily assessed using BCS, whilst the clinical significance is determined by a physical examination, owner-reported information and laboratory findings. It is hoped that this approach will provide greater clarity in management and emphasize the need to address comorbidities alongside weight reduction. Ultimately, recognizing obesity as a multifactorial and interrelated condition enables more individualized, prioritized, and effective interventions to improve pet health and quality of life.

 

References

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