Obesity

The BSAVA defines obesity as “a condition characterised by excess adiposity, arising from multifactorial causes which, in some cases, can have both direct and indirect health consequences.”  As obesity develops, body fat accumulates in both subcutaneous and visceral (abdominal) locations, the physical and visual signs of which are readily evident on a clinical examination.  The health consequences of this fat accumulation can be highly variable, ranging from a seemingly minimal impact to marked impairment of organ function and daily activity.  When dogs and cats suffer such impairments, their obesity is defined as ‘clinical obesity’ (see below); given that the excess adiposity is the direct cause of illness in these cases, clinical obesity is considered to be a disease in its own right.

The BSAVA recommends that veterinary professionals assess adiposity in dogs and cats using the one-to-nine (1-9) body condition score (BCS) scale.  The most widely-used clinical method for determining adiposity is assessing body condition, with the 9-unit scale being the most extensively validated and the one recommended by the WSAVA Global Nutrition Panel.  Dogs and cats with BCS 8 or 9 have an ‘obese phenotype’, equivalent to at least 30% excess weight, whilst those with a BCS 6 or 7 have an ‘overweight phenotype’.  Alternative methods of assessing adiposity include precise techniques, such as dual-energy X-ray absorptiometry, and other clinical measurements including body fat index and zoometry (tape measure).  Although measuring bodyweight is not a reliable method of determining body fat mass specifically, it is precise and accurate.  Therefore, bodyweight measurement can be used to monitor changes within an individual animal (for example, identifying a subtle increase in weight over time) that can then prompt early intervention.

When a dog or cat is identified with excess adiposity, the BSAVA recommends determining whether ‘clinical obesity’ is present.  ‘Clinical obesity’ is defined as a chronic illness that results from alterations in organ or whole-body function that are directly induced by excess adiposity, independent of the presence of other adiposity-related diseases.¹  Affected dogs and cats have clinical signs or biochemical changes directly attributable to obesity-related organ dysfunction, and/or have age-adjusted impairments in quality of life and mobility.  In contrast, animals with ‘pre-clinical obesity’ have excess body fat, but do not have any related clinical signs or functional impairments.¹ Although not currently impacted, animals with pre-clinical obesity are at risk of progressing to the clinical form or developing obesity-associated diseases.

To determine whether a particular case of obesity is ‘pre-clinical’ or ‘clinical’, a veterinary clinical assessment is required, with investigations including history, physical examination and additional investigations (e.g. blood tests and diagnostic imaging) if necessary.

The BSAVA recommends fully assessing dogs and cats with obesity for the presence of other diseases.  It should be noted that the ‘illness’ associated with clinical obesity includes only those clinical signs and functional impairments that are a direct consequence of the excess adiposity (e.g. altered musculoskeletal function such as gait changes or inability to jump; altered respiratory function such as breathlessness on exercise, altered breathing patterns and snoring); it does not include indirect consequences such as clinical signs arising from diseases that the obesity might have caused e.g. osteoarthritis.  This is because the definition of one disease (i.e. in this instance, clinical obesity) should not be contingent on the presence of another (e.g. diabetes mellitus).² Nonetheless, determining the presence of other diseases is still important, so that the impact of the excess adiposity on health can be fully determined.  Therefore, when present, any conditions directly due to obesity and comorbidities ideally should both be fully investigated, enabling the most appropriate therapy to be included in a specific obesity care plan.

For dogs and cats with obesity, the BSAVA recommends a care plan, comprising weight reduction and subsequent maintenance, treatment for direct effects of obesity if necessary, and also appropriate treatment for any obesity-associated diseases or comorbidities.  The therapeutic weight reduction phase involves the animal gradually losing weight towards a pre-determined target, set based on the specific aims for that case (e.g. improving mobility, lessening the impact of an associated disease, preventing future obesity-associated diseases from developing).³  After the target weight is reached, a weight maintenance plan should be implemented, where the aim is to prevent regain.

The main current strategy for therapeutic weight reduction is dietary energy restriction, by feeding a purpose-formulated diet, coupled with increasing physical activity and close monitoring from a veterinary professional.  Such diets improve owner compliance and many weight loss outcomes (e.g. rate of weight loss, percentage weight loss, chances of reaching target weight), whilst reducing the risk of nutrient deficiencies developing, and decreasing the chances that regain of weight will occur after target weight is reached.³  Although increasing physical activity does not lead to meaningful weight reduction in isolation⁴ , there are likely to be other benefits including minimising loss of muscle.⁵

Recently, effective pharmaceuticals have been licenced for weight loss in people with obesity, with available drugs including semaglutide and tirzepatide.⁶ Currently, no licenced pharmaceutical agents are available for the treatment of obesity in companion animals, although such drugs might become available in the future.  For now, insufficient evidence exists to make any recommendations for off-label use of drugs licenced for humans.  Bariatric surgery is also an effective method of weight reduction in people with obesity,⁷ but similar techniques have not yet been used clinically in dogs and cats and, therefore, cannot be recommended or be regarded as normal veterinary practice.

The BSAVA emphasises the need for veterinary professionals to focus on prevention of obesity as well as treating animals with existing obesity.  Given that rapid growth is associated with future risk of obesity in both dogs and cats, prevention strategies should start early in life.  A monitoring programme of weight and BCS should commence during a puppy’s or kitten’s growth phase, taking account individual breed variability.^8,9  Regular weight (e.g., monthly) checks during growth are advisable, although more frequent checks (e.g. every 2 weeks) should be considered around the time of neutering.  In adult dogs, weight and BCS checks should ideally be conducted at least once a year, but more frequently if feasible, with details recorded in the clinical records.  More frequent weighing is strongly advised in animals at risk of obesity (e.g. predisposed breeds, neutered animals, and those that have previously been overweight).  Such a strategy would often highlight unwanted weight gain, which can then be addressed early in the disease process through adjustments to diet and exercise.  Home weighing (for example, using bathroom scales or weighing in a pet carrier with digital luggage scales) is an alternative where an owner is reluctant to bring their pet to the clinic for weight checks.

Successful prevention requires a commitment of owners to modify and control their pet’s behaviour over the long term. A complete and balanced diet should be fed that is appropriate for the life stage and lifestyle. The amount fed should be measured accurately (e.g. using scales) and adjusted according to changes in bodyweight and BCS.  Care should be taken when feeding high energy diets (i.e. diets designed for working dogs), which would not be a suitable choice for most pet dogs.  The amounts of any additional foods (e.g., treats) should be carefully controlled and taken into account in the overall daily energy intake.  Dogs and cats should also have opportunities for regular physical activity.  For dogs, regular walks and play activity are most commonly used; for cats, providing outdoor access (if safe to do so) or regular play sessions can be considered.

The BSAVA would encourage veterinary surgeons to hold supportive, non-judgemental conversations with owners of pets who have obesity.  Care should be taken when holding conversations about obesity with owners, since this is a highly stigmatised condition and a considerable societal “weight stigma” exists.  Evidence in humans suggests that stigmatising people with obesity threatens health and interferes with effective obesity management.¹⁰ Weight stigma is also observed in veterinary professionals, and is directed towards both dogs and their owners¹¹, with such stigma adversely affecting treatment recommendations.  In light of these findings, veterinarians should pay attention to pre-existing biases, and the potential impact these can have on clinical decision making.  Conversations with owners should be empathic, use non-stigmatising terms and, above all else, facilitate the access of pets with obesity to the veterinary care that they need to improve their health and welfare.

There are various direct health and welfare effects for dogs with either an overweight or obese phenotype, including a shorter median lifespan,^12,13 poorer quality of life,^13,14 metabolic derangements^15-17 and functional impairment (most notably respiratory, cardiovascular and renal),^18-21 as well as predisposition to various comorbidities.²²  Overall, a BCS of either 4/9 or 5/9 are optimal both for maximal longevity and minimal risk of developing obesity-associated diseases.  However, the situation in cats is more complicated.  Cats with either an overweight (BCS 6-7/9) or obese (BCS 8-9/9) phenotype are predisposed to several comorbidities^23-25 and metabolic derangements,²⁶ but shorter lifespan is only seen in cats with BCS 9/9, whilst cats with a BCS of 6/9 actually have the longest average lifespan.²⁷  Overall, therefore, a BCS of either 5/9 or 6/9 could be considered optimal body condition in cats, depending on which health benefit (disease risk vs. lifespan) is prioritised.

In January 2025, a commission of international experts, assembled by the Lancet to clarify diagnostic criteria for obesity in people, reported its findings.² They decided on the following overarching definition of obesity: ‘a condition characterised by excess adiposity, with or without abnormal distribution or function of adipose tissue, and with causes that are multifactorial and still incompletely understood’.²  The definition of obesity in dogs and cats detailed above has been adapted from this definition.¹  A longstanding controversy has been whether the condition should be considered as a disease.²⁸  Proponents argue that the condition meets established disease criteria and that pathogenetic mechanisms are well defined;²⁹ opponents argue that excess adiposity merely acts as a risk factor for other diseases, and arises as a physiological response to excessive food intake or other lifestyle factors.³⁰  The Lancet Commission recognised that both perspectives had merit.²  Put another way, whether obesity is considered to be a disease depends upon the individual circumstances of a particular case; in some cases, adverse effects on health are considerable (in human patients including sleep apnoea; metabolic derangements such as hyperglycaemia and hyperglyceridaemia; impaired mobility; and significant impact on daily living); however, in other cases, sometimes with a similar degree of excess adiposity, very few health impairments are apparent.  The crucial distinction, therefore, is the presence of ‘illness’, defined as ‘deviations from the healthy functioning of tissues, organs or the whole organism’.² Therefore, the Commission proposed sub-defining cases of obesity as follows:

• Clinical obesity: a chronic, systemic illness characterised by alterations in the function of tissues, organs, the entire individual, or a combination thereof, due to excess adiposity.²
• Preclinical obesity: a state of excess adiposity with preserved function of other tissues and organs and a varying, but generally increased, risk of developing clinical obesity and several other non-communicable diseases (e.g., type 2 diabetes, cardiovascular disease, certain types of cancer.²

The definition of obesity in dogs and cats proposed by the BSAVA has evolved to follow a similar framework.  Determining whether a particular animal has clinical or preclinical obesity requires a clinical assessment by a veterinary professional, with the extent of that assessment depending on individual circumstances.  As a minimum, a history should be taken and a physical examination performed.  In some cases, additional investigations (e.g. blood tests and diagnostic imaging) might be required.  Such investigations may also be required when either obesity-associated diseases or comorbidities are preset.  A potential diagnostic challenge is determining whether some clinical signs (e.g., mobility issues, respiratory signs) are directly related to the excess adiposity or to an associated disease when both are present.  For example, it might be difficult to determine whether impaired mobility is directly due to obesity or is instead caused by concurrent cruciate ligament disease.  In such cases, clinical signs from other body systems (e.g., snoring, abnormal blood test results such as hypertriglyceridaemia or hypercholesterolaemia) might enable the presence of clinical obesity to be confirmed.  However, if this is not possible, it is better simply to list obesity and the other disease as diagnoses (e.g., obesity and cruciate ligament disease) but not attempt to distinguish between clinical or preclinical.¹

Therapeutic weight reduction is the process of inducing weight loss, in a controlled fashion, in order to reduce adipose tissue mass in order to improve health. Ideally, it should only be undertaken when the animal is systematically well, and there are no concurrent burdens on their metabolic or nutritional status (e.g., growth, pregnancy, lactation or periods prolonged physical activity such as endurance events).  The exact food used for weight management is a matter of choice for the owner, after a discussion with a veterinary professional, with the key priorities being to ensure that it is both safe (i.e. ensuring all essential nutrient requirements are met) and effective.  If the dog or cat has a BCS of 6 and is being fed a complete and balanced diet, a modest reduction (20% maximum) in intake of their current food might be effective.³¹  However, successful weight loss for dogs and cats with a BCS 7 and above usually requires marked energy restriction for a prolonged period,^32-34 and feeding a diet designed for maintenance in such circumstances (including those marketed as “light’ diets) can potentially lead to essential nutrient deficiencies.^35,36  Nutrient deficiencies are far less likely when a diet is fed that is purpose-formulated for weight loss.^37,38 This can either be achieved by feeding a manufactured weight management diet or a home-prepared diet to a recipe formulated by an appropriately-qualified veterinary clinical nutritionist. As well as reducing the risk of nutrient deficiencies, other benefits include decreasing voluntary food intake^39,40 and reducing the risk of weight regain after target weight is reached.⁴¹ The intake of additional food items (e.g. food rewards and table scraps) should be minimised to ensure that the overall diet does not become unbalanced.  If treats are used, these should be incorporated into the daily food requirement calculation.

In cats and dogs with obesity, rates of weight loss of between 0.5% and 2.0% per week are reported,⁴² although average rates are usually <1% per week in pet dogs and cats.^31,32  The more marked the reduction in food intake, the faster the rate of weight loss, but this can also has been associated with a greater loss of muscle mass.⁴¹  Furthermore, loss of muscle mass increases as percentage weight loss increases.^33,34  Therefore, targets for obesity care plans should prioritise health and wellbeing benefits rather than rates or percentages of weight loss.  Whilst suitable targets for weight loss are not well defined, modest amounts of weight loss (i.e. 6-9% of existing body weight) can be sufficient to produce measurable benefits to health.⁴⁴  However, weight loss might be unsuitable in some cats and dogs, such as those with another significant life-limiting disease (e.g. metastatic neoplasia, end-stage liver or kidney disease).

The two main drugs licenced for treatment of obesity in people are semaglutide (a glucagon-like peptide [GLP-1] agonist) and tirzepatide (a combined GLP-1 and gastric inhibitory polypeptide receptor agonist).³  These drugs have both central and peripheral actions to increase insulin secretion and decrease appetite.³  It is likely that these drugs will have a similar effect in dogs and cats with obesity, although current evidence is lacking.  As and when such drugs do start to be used, veterinary professionals would no longer need to make accurate calculations for daily food intake because a negative energy balance will be achieved by the drug’s effect on appetite.  Further, there would be less of a need to feed a food with increased fibre content designed to promote satiety.  However, it would still be necessary to feed a diet supplemented with essential nutrients (relative to energy content) to prevent the risk of nutritional deficiencies^35-38,45.

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11. Pearl RL, Wadden TA, Bach C, Leonard SM, Michel KE. Who’s a good boy? Effects of dog and owner body weight on veterinarian perceptions and treatment recommendations. Int J Obes (Lond). 2020 Dec; 44(12):2455-2464. doi: 10.1038/s41366-020-0622-7
12. Kealy RD, et al. J Am Vet Med Assoc. 2002; 220: 1315-1320.
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28. American Medical Association House of Delegates. Recognition of obesity as a disease. Resolution 420 (A-13).  https://www.npr.org/documents/2013/jun/ama-resolution-obesity.pdf?t=1544195051473
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WSAVA Global Obesity One Health Meeting resources

https://www.sciencedirect.com/journal/journal-of-comparative-pathology/special-issue/1066455CB17

WSAVA Global Nutrition guidelines on BCS

https://wsava.org/global-guidelines/global-nutrition-guidelines/

FEDIAF Guidelines

http://www.fediaf.org//prepared-pet-foods/nutritional-requirements.html

Reviewed by Alex German and members of BSAVA Scientific Committee (Nikki Bentley, Rachel Casey, Gillian Diesel, Ben Garland, Macauly Gatenby, Rachel Lumbis, Jasmine Malm, Michael Rampersad, Caroline Scobie, James Warland) 2025.