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Diseases & Conditions That Contribute to Obesity in Cats
Veterinary & Aquatic Services Department, Drs. Foster & Smith
Weight Control
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Cats may become overweight for many reasons. Whether the obesity is due to simple overfeeding or a result of a disease process, the bottom line is the same: the cat is taking in more calories than he is using. Regardless of the cause of obesity, the owner is ultimately responsible for regulating the cat's caloric intake and use, and in seeking veterinary assistance in maintaining the cat at the optimal weight. Humans are the main cause of obesity in cats.

Some of the more common diseases and conditions which can contribute to obesity in the cat are discussed below.

  1. Food type, availability, and palatability: Some cats will only eat what they need and do fine if their food is available free choice (available at all times). Others will eat as much as is available and then look for more. Many cats are finicky and others will eat just about anything. So the amount and type of food that is fed and the eating tendencies of the cat can determine how likely it is a cat will become overweight.

    The type of food fed has a direct bearing on the tendency of a cat to become overweight. Table scraps, treats, even premium high-energy cat foods can contribute to obesity. A 7-year-old lap cat whose main exercise is walking to and from the food bowl does not need a high-energy cat food, whereas his brother who is a barn cat and lives outside has high energy needs and a more high energy food may be in order (depending upon the number of mice caught!).

  2. Activity level: Activity level plays a major role in determining the caloric needs of a cat and thus his tendency to become overweight. An active cat will use more calories.

Humans are the main cause of obesity in cats.
Neutered and spayed cats, in general, need fewer calories than intact cats.
  1. Neutering and spaying: Neutering and spaying cats lowers their metabolic rate such that they require fewer calories than intact cats. In addition to changes in metabolism, androgens and estrogens (male and female sex hormones, respectively) stimulate roaming behavior and general physical activity. Estrogen, in addition, has the effect of decreasing appetite. Spayed cats never have the extra energy demands of pregnancy or raising a litter.

    Neutered and spayed cats require only 75-80% of the food given to intact cats. Since their energy needs are less, if we feed spayed and neutered cats what we would feed intact cats, they will, of course, gain weight. In truth, most neutered and spayed cats are overfed and underexercised and are twice as likely to become obese as intact cats. Neutering and spaying in themselves do not cause obesity, it is how we care for the cats afterwards that predispose them to becoming overweight.

  2. Genetics and breed predispositions: Are some breeds simply more prone to becoming overweight? The answer is not as clear as it is in dogs. We know that some breeds of dogs are predisposed to obesity. In cats, it has been found that mixed breeds may have more of a tendency to become overweight than purebreds such as the Abyssinian.

    Genetic factors which influence the type and characteristics of fat produced by the body have been shown to contribute to obesity in rats and mice. Such factors may occur in cats.

  3. Age: Cats tend to become overweight when they are between 2 and 12 years of age, especially around the 6 year mark. As cats become 'senior,' the tendency to become overweight decreases. Young cats, too, in general, are less likely to be overweight, since their energy requirements are high since they are growing and are generally more active.

  4. Social environment: Many people will acknowledge they eat more when they are stressed, and often eat less nutritious food. For me, large amounts of chocolate come to mind. Some cats may have similar responses to stress.

    Cats who live in a multi-cat or even multi-pet households may tend to eat more and/or faster than those in one-cat households. The change in behavior when other animals are present is called 'social facilitation.' The competition for food, whether perceived or actual, makes some cats much more focused on their food and can lead to obesity.

  5. Physical Environment: Maintaining body temperature is an energy-consuming task. When a cat is in an environment with a temperature below freezing, his calorie requirements increase dramatically. Conversely, an inside cat uses relatively few calories to maintain normal body temperature.

  6. Medications: Various medications can influence metabolism and appetite. These include the glucocorticoids such as prednisone and dexamethasone, the barbiturates such as phenobarbital which is used to control epilepsy, and a class of drugs called benzodiazepines which includes valium.

  7. Hypothyroidism: In the disease hypothyroidism, the cat's body produces less thyroid hormone. Thyroid hormone influences metabolic rate. Less thyroid hormone means lower metabolic rate and lower energy needs. A normal cat will become overweight if he develops hypothyroidism and is fed the same amount he was fed when he was healthy. Hypothyroidism is an uncommon condition in cats, but it can occur.

    It is very difficult to get a hypothyroid cat to lose weight even when fed a weight reduction diet. By treating the hypothyroidism in conjunction with starting a weight control program, chances of success are much higher.

  8. Cushing's disease (hyperadrenocorticism): Cushing's disease is a disease in which the adrenal gland produces too high a level of glucocorticoids. Glucocorticoids can alter metabolism and cause an increase in appetite and an increased deposition of fat. Again, in addition to starting a weight control program, the Cushing's disease must be managed if the cat is to successfully lose weight. Cushing's disease is uncommon in cats, but can occur.

  9. Insulinoma: An insulinoma is a tumor that occurs in the pancreas. It is a tumor consisting of the cells that produce insulin. A cat with an insulinoma produces too much insulin. Insulin tends to increase food intake and promote the generation of tissue, including fat. Insulinomas are rare in cats.

  10. Pituitary gland and brain diseases: The pituitary gland is often called the 'master gland' because it produces hormones itself and regulates the production of hormones from most of the other glands. If the pituitary gland is functioning abnormally, changes in the levels of various hormones can change the cat's metabolism, appetite, and fat deposition.

    The hypothalamus in the brain regulates appetite. Hypothalamic abnormalities could account for rare instances of increased appetite resulting in obesity.


References and Further Reading

Burkholder, WJ; Thatcher, CD. Canine and feline obesity. Veterinary Forum. 1995;February:54-58.

Hills Pet Nutrition, Inc. Nutrition and the Management of Weight Control. In Healthcare Connection: Clinical Module Level II: 117-154.

Markwell, PJ. Canine Calorie Control. In: Applied Clinical Nutrition of the Dog and Cat. Waltham USA:103-122.

Wolfsheimer, KJ. Obesity. In Ettinger, SJ; Feldman EC (eds): Textbook of Veterinary Internal Medicine. W.B. Saunders Co. Philadelphia, PA; 2000;70-72. 

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