Obesity in cats is defined as being more than 20 percent over their ideal body weight, and it is estimated that globally, approximately 40 percent of cats are overweight and obese (Royal Canin, unpublished review). The prevalence of cats that are overweight and obese is also impacted by life stage, with the highest prevalences in the adult and mature stages. Overweight and obesity rates have been increasing in the feline population, and there is evidence of a greater proportion of cats presenting with severe obesity (with a body condition score (BCS) over 9) in recent years (Broome et al., 2023).
A range of diseases are associated with obesity, including oral, gastrointestinal and urinary diseases, dermatopathy and diabetes mellitus (Lund et al., 2005; Teng et al., 2018a). In addition, while obesity negatively impacts the quality of life in some cats (Hanford and Linder, 2021), its impact on reduced longevity is well documented in large retrospective population-based studies (Teng et al., 2018b; Montoya et al., 2023).
Overweight and obesity rates have been increasing in the feline population, and there is evidence of a greater proportion of cats presenting with severe obesity (with a body condition score (BCS) over 9) in recent years
Diagnosis of overweight and obesity
When a cat’s ideal body weight is known, the most accurate way to determine the development of overweight and obesity is to track body weight changes. Previous campaigns such as the PDSA’s “Big Weigh In” campaign (Veterinary Practice, 2023) can help to increase awareness of the importance of regular weighing. A BCS (Figure 1) can also be attributed to the cat to subjectively estimate the degree to which it is overweight (Laflamme, 1997); however, there is room for improvement in the frequency of recording of both body weight and BCS (Taylor et al., 2022). Care in the nature of communication with the cat owner is paramount to ensure their active participation in the weight management plan (Phillips et al., 2017; Sutherland et al., 2022). Veterinary nurses and technicians can also play key roles in building trust and imparting additional knowledge to the pet owner, especially around key procedures such as sterilisation.
Implementation of a weight loss plan
On diagnosis of obesity by a veterinarian, a therapeutic weight loss diet should be prescribed. Therapeutic weight loss diets are specially formulated to contain the necessary levels of essential amino acids, overall protein, and individual vitamins and minerals necessary during a period of caloric restriction. Such formulas often feature a low energy density to facilitate dietary energy restriction and may be designed to have satietogenic properties (Bissot et al., 2010). In the author’s experience, caloric allocation starting at 53kcal/kg (68 percent of maintenance energy requirement (MER)) using therapeutic weight loss diets can be implemented safely without adverse effects in cats, while minimising nutritional deficiencies (German et al., 2023). However, care must be taken as a wide variation in recommended calorie intake, dietary caloric density and cost exists among diets marketed for weight loss in pets (Linder and Freeman, 2010).
Care must be taken as a wide variation in recommended calorie intake, dietary caloric density and cost exists among diets marketed for weight loss in pets
Some reduced-energy (“light”) maintenance diets (ie diets not formulated for therapeutic weight loss) can be fed to 68kcal/kg (80 percent MER), and while this approach will not achieve the same weight loss rates as those that could be achieved using therapeutic weight loss diets, no clinical evidence of essential nutrient deficiencies were observed in cats in a recent study using this approach (Keller et al., 2020).
The use of diets not formulated for weight loss may result in key nutrient deficiencies, as has been observed in dogs (Gaylord et al., 2018), with potential long-term health impacts. Online tools exist to calculate the quantity of therapeutic wet and/or dry diet necessary to target a weight loss rate of between 0.5 and 2 percent per week, which is considered safe and achievable in most cats (Flanagan et al., 2018). Adjustment of the ration in increments of 5 to 10 percent is recommended to help maintain weight loss after the initial period, as the rate of weight loss has been found to be positively associated with the successful completion of a weight loss programme in cats (O’Connell et al., 2018). The use of weighing scales to accurately portion meals is an integral part of a weight loss programme (German, 2022). Further, increasing activity after initial weight loss may be beneficial for overall feline health but can be difficult to implement and is unlikely to significantly impact body weight or weight loss.
Online tools exist to calculate the quantity of therapeutic wet and/or dry diet necessary to target a weight loss rate of between 0.5 and 2 percent per week, which is considered safe and achievable in most cats
In terms of diet characteristics, it has been reported that increasing dietary moisture up to 80 percent on an as-fed basis decreases the voluntary caloric intake in cats fed ad libitum (Wei et al., 2011). In dogs, it has been found that reducing the volumetric density of dry diets resulted in decreased spontaneous food intake (Serisier et al., 2014); however, it is unclear if the same strategy would be beneficial in cats. Finally, most cat owners enjoy providing treats in one form or another to their cats, but most do not ration treats depending on their cat’s BCS (Box 1) (Nielsen et al., 2024). Treats can be incorporated into a weight loss plan but should not comprise more than 10 percent of the total caloric intake and should be accounted for in the diet allocation calculation.
| – Maximise the proportion of calories coming from wet diets, as long as the cat will accept it – Split into multiple meals per day where possible – Provide largest meal in the evening to avoid begging behaviour overnight – Add in low-calorie foods such as cucumber to manage begging – In multi-cat households, feed cats in different rooms – Weigh the cat regularly and weigh the food provided daily |
Weight maintenance post-weight loss
Once the targeted body weight has been achieved, the cat will enter into a phase of weight maintenance. On average, the energy needs of the cat post-weight loss are 14 percent higher than what was required during weight loss (German et al., 2021). With this in mind, it is highly recommended that the cat continues on a therapeutic weight loss diet, but if that is not possible, that a low-energy diet is provided that meets the nutritional requirement of the cat and does not result in limiting key nutrients (Keller et al., 2020). Maintaining weight post-weight loss can be a challenge, with cats that rebound more likely to gain 50 percent of the weight that they had lost (Deagle et al., 2014). The long-term success of a weight loss plan depends on modifying the daily habits of those taking care of the cat, and the implementation of a routine of weighing the cat and weighing the food can help to keep on the right track.
Comorbidities and nutritional management
Common comorbidities observed in overweight and obese cats include adverse food reactions, dermatological and gastrointestinal issues, endocrinological diseases such as diabetes mellitus, dental disease, and orthopaedic and urinary complications (Chiang et al., 2022; Lund et al., 2005; Teng et al., 2018a). In the case of comorbidities, bringing the cat back to a BCS of 5/9 may not be in the cat’s best interests. For example, chronic disease processes such as renal disease result in emaciation, therefore having a certain level of excess weight could be beneficial for long-term health. Nevertheless, while negative associations have been found between rates of overweight and obesity with age (Teng et al., 2018b), these results need to be interpreted with caution as survivorship bias may play a role (Chiang et al., 2022). Partial weight reduction programmes in cats with obesity can lead to faster weight loss rates and involve fewer clinic visits, compared with complete protocols (German et al., 2023).
Overweight and obese cats suffering from adverse food reactions and dermatological issues may benefit from a diet formulated for their specific needs, fed at slightly less (90 percent MER) than energy requirements for weight maintenance, to result in a slow but safe weight loss
Overweight and obese cats suffering from adverse food reactions and dermatological issues may benefit from a diet formulated for their specific needs, fed at slightly less (90 percent MER) than energy requirements for weight maintenance, to result in a slow but safe weight loss. Evidence exists that weight loss is associated with an increased probability of a diabetic cat going into remission (Gostelow and Hazuchova, 2023); however, prospective studies are lacking in this area. The author is not aware of a commercially available diet tailored for cats with concurrent chronic kidney disease (CKD) and obesity; targeting a slower weight loss and prioritising the nutritional management of CKD above optimal weight loss could bring long-term benefits. Overall benefits of weight loss in cats suffering from overweight and obesity include increased mobility, enhanced quality of life and reduced food-seeking behaviour as perceived by their owners (Flanagan et al., 2018).
Conclusion
Feline obesity is a chronic disease which negatively impacts a cat’s quality of life and longevity, and results in increased prevalence of other metabolic diseases. Upon diagnosis, and having onboarded the cat owner, a weight loss plan comprising a therapeutic diet in combination with caloric restriction can help to safely bring the overweight cat back to a pre-determined healthy adult body weight. Specific nutritional solutions exist for cats with obesity, and comorbidities can be managed simultaneously. Changing the behaviour of those in the cat’s environment is key to making the weight loss plan a long-term success.
