Obesity is a growing concern for both humans and pets! That’s why I wanted to make a series of blog articles to raise awareness of this disease and to help you if your cat is concerned. In the next articles, I will explain what obesity is, what are its consequences, how to recognize if your cat is overweight or obese, what are the main causes of obesity, and finally, how to make your cat lose weight. Disclaimer: I’m not a vet. If your cat has any health issue, go to see your vet.

What is obesity?

Obesity is scientifically defined as an excess of body fat, which results in an impairment of health or body function. It’s generally estimated that a cat starts being considered as obese when it weighs more than 20% of its ideal body weight. A cat starts being considered as overweight when its body weight exceeds 10% of its ideal weight. For example, if your cat’s ideal weight is 3.4 kg (7.5 lbs), your cat is to be considered obese if it weighs more than 4.1kg (9 lbs), with 20% of 3.4 kg being 0.7 kg (1.5 lbs). These 700 grams (1.5 lbs) may seem like a very small amount, but if you translate this extra 20% of body weight to a human scale, these additional 700 grams (1.5 lbs) for your cat are equivalent to an additional 12 kg (26.5 lbs) for a 60 kg (132 lbs) person! It’s been estimated that 20 to 52% of cats are overweight or obese in western countries, depending on the studies. Moreover, the prevalence of obesity in cats is currently increasing and it really is an epidemic like it is for humans, making it the second most common health issue for cats!

Is my cat obese or overweight?

Weigh your cat

The easiest and obvious way to check whether a cat is obese or overweight is to weigh it (if you know the ideal weight of your cat)! If your cat’s weight is superior to more than 10% of its ideal weight, your cat is overweight. Tip: If you don’t manage to make your cat stay on a balance, or your cat is too light for the balance to detect it, I advise you to use the following method: weigh yourself while holding your cat, then weigh yourself again without the cat and subtract the two readings.

Body Condition Score

If you don’t know the ideal weight of your cat, one of the best ways to assess the fitness of your cat is to use the Body Condition Score. It is a scale based on visualization and palpation which helps evaluating if your cat is underweight, ideal or overweight. Two versions of this scale exist, one scaled from 1 to 5 (with 3 being the ideal weight), and the other one which gives more nuances on your cat’s weight going from 1 to 9 with 5 being the ideal weight. cat body condition score
Body Condition Score (click to see it in bigger)
When looked from above, you should be able to see a waistline after the ribcage of your cat, and you should also see an abdominal tuck. When palpating your cat you should be able to easily feel the ribs (you should not have to press), but the ribs shouldn’t be visible. When doing a body condition score, be honest with yourself, you won’t be helping your cat by underestimating its body score! If you have difficulties to evaluate the body condition score, you can ask your vet to show you how to do it.

Feline Body Mass Index

There are also other, less subjective, ways to evaluate if your cat is at its ideal weight, for example by using a feline BMI (Body Mass Index). I found two different formulae for computing the feline BMI:
  • The first one gives you the percentage of body fat of your cat, and it’s calculated from the rib cage circumference and the length of the lower back leg from the knee to the ankle (look at the picture to know which part to measure). Your cat is considered underweight if the body fat is inferior to 15, overweight if it’s above 30 and very overweight if it’s above 42. Bodyfat(%)={[(Ribcage/0.7067)−LBL]/0.9156}−LBL If you don’t want to make the calculations yourself you can find a helpful calculator here.
  • cat lower back leg
    The part of the leg you need to measure
  • Another feline BMI formula has been developed more recently. This feline BMI formula is fBMI = BW / length of the lower back leg. A cat is considered overweight if it has a fBMI greater than 32.
I didn’t find many studies that use the feline BMI. Moreover, the fBMI may not be very precise as it can be difficult to measure the ribcage or lower back leg of your cat precisely. Nevertheless, I think it still can be very useful to know if your cat is more on the thin or on the overweight side.


A quick rule of thumb that you could use and that was suggested by a study on non-pedigree cats is the following. If you have a domestic shorthair or domestic longhair of average size, the threshold for being overweight was set at 5.5 kg (12.1 lbs) in males and at 4.5 kg (9.9 lbs) in females. This means that if your cat’s weight is above these thresholds, it is very likely that it’s overweight or even obese. Take this rule of thumb with a grain of salt, as the study was made on only 101 cats and it may not apply to your cat if your cat is very tall or very small. Finally, if you are still not sure if your cat is overweight or not, the best way to know is to ask your vet. You can also ask your vet what should be the ideal weight for your cat, so you can have a reference for the future. It’s important that you take the lead and explicitly ask your vet: in many cases, vets are reluctant to tell the owners that their cat is overweight or obese to not offend them!

Consequences of obesity

Obesity is often classified in itself as a disease, and is considered the second most common health problem in cats after dental diseases! In fact, obesity is an inflammatory condition that increases oxidative stress and insulin resistance. Obese cats are 4 times more likely to get diabetes and 5 times more likely to develop lameness. Many other diseases can be caused by obesity or are at an increased risk. Here is a nonexhaustive list:
  • Urinary tract disease such as acute cystitis,bladder stones, feline urologic syndrome, obstruction, urinary tract infection;
  • Oral diseases such as gingivitis, periodontal disease, stomatitis;
  • Dermatologic disorders, as the cat is not able to groom itself efficiently;
  • Risk of tumors;
  • Hepatic lipidosis;
  • Osteoarthritis.
fat-red-cat Obesity makes the clinical evaluation of these diseases more difficult for the vet, for example in the case of palpation. It also increases the risk associated with anesthesia. Obesity, in addition to increasing the risk for all these diseases, will reduce the quality of life of your cats, as obese cats will develop heat and exercise intolerance. Finally, for all these reasons obesity will shorten the life expectancy of your cat. To summarize, obesity should be taken very seriously as it can and will have serious consequences on the health of your cat. Moreover, studies have shown that even being moderately overweight can increase the risk of chronic health problems. I know that many of you will read that, and think “my cat is a bit chubby and perfectly healthy”: your cat may be one of the lucky exceptions, but your cat may also not have suffered the consequences yet. It’s also important to take into consideration that cats are incredibly good at hiding their pain and may well be hiding a disease. That’s why for me it’s important to do everything to reduce these risks, meaning that you really should keep your cat at a healthy weight. Now that we know what obesity is and its consequences, in the next blog articles I will explain what the causes of obesity are and how to prevent it. Finally, I will write an article on how to make your cat lose weight if it needs to. Sources Kawasumi K, Iwazaki E, Okada Y, Arai T. Effectiveness of feline body mass index (fBMI) as new diagnostic tool for obesity. Jpn J Vet Res. 2016;64:51–56. http://www.felinediabetes.com/FelineBMI.pdf Cave, NJ, Bridges, JP, Weidgraaf, K, Thomas, DG. Nonlinear mixed models of growth curves from domestic shorthair cats in a breeding colony, housed in a seasonal facility to predict obesity. J Anim Physiol Anim Nutr. 2018; 102: 1390– 1400. Alexander J. German, The Growing Problem of Obesity in Dogs and Cats, The Journal of Nutrition, Volume 136, Issue 7, 1 July 2006, Pages 1940S–1946S, Chandler, M, Cunningham, S, Lund, EM, Khanna, C, Naramore, R, Patel, A, Day, MJ (2017) Obesity and associated comorbidities in people and companion animals: A one health perspective. Journal of Comparative Pathology 156: 296–309. Lund et al., 2005, E. Lund, P.J. Armstrong, C.A. Kirk, J.S. Klausner, Prevalence and risk factors for obesity in adult cats from private US veterinary practices, International Journal of Applied Research in Veterinary Medicine, 3 (2005), pp. 88-96 Debra L. Zoran, Obesity in Dogs and Cats: A Metabolic and Endocrine Disorder, Veterinary Clinics of North America: Small Animal Practice, Volume 40, Issue 2, 2010 Sandøe, P., Palmer, C., Corr, S., Astrup, A., Bjørnvad, CR.(2014) Canine and feline obesity: a One Health perspective Veterinary Record 175, 610-616. Wall M, Cave NJ and Vallee E (2019) Owner and Cat-Related Risk Factors for Feline Overweight or Obesity. Front. Vet. Sci. 6:266. doi: 10.3389/fvets.2019.00266