According to a 2015 survey by the Association for Pet Obesity Prevention, 58% of cats in the United States are overweight. Overweight animals are more susceptible to the development of health problems such as diabetes mellitus, lameness, and nonallergic skin conditions. In addition, an overweight body condition may be associated with increased oxidative stress on feline cells and tissues. Obesity in a cat is considered to be present when the animal’s body weight is >25% greater than ideal for that individual.

Many owners are aware of the health risks associated with an overweight or obese body condition in their pets, but are still reluctant to put the cat on a diet. Caregivers are frequently concerned that restricting the cat’s food intake may strain or break their bond with their pet and cause the cat to exhibit annoying behaviors associated with hunger such as excessive meowing, continual begging, or even owner-directed aggression.

This study included 58 client-owned, indoor-only, adult neutered cats, both male and female, all of whom were 25% or more over their ideal body weight.  All animals had normal physical examination findings apart from obesity, and also had normal clinicopathologic findings (biochemical panel, complete blood count, and serum thyroxine). Owners of cats enrolled in the study were required to control the pet’s environment so that there was no access to human or other pet food in the home.

Each cat was enrolled in the study for 10 weeks, the first two weeks of which was the time allotted for the cat to be gradually transitioned from their regular diet to the test diet. No restriction in the amount of food given to the cat was implemented in these first two weeks. Each of the subjects was fed one of three equicaloric diets: a high-fiber (HiFi) diet, a control diet designed to maintain weight in adult cats, or a low-carbohydrate/high-protein diet. The researchers and owners were blinded to the type of diet fed to each cat during the study.

For the remaining  8 weeks of the study, owners were required to feed a measured amount of the prescribed food based on the cat’s ideal body weight and maintain a diary of the cat’s behavior. If the cat rejected the diet, it was excluded from the study.  At the beginning of the study, owners completed a questionnaire that included questions about the cat’s appetitive behaviors (behaviors the cat displayed when he or she was hungry) as well as behaviors the cat demonstrated when the cat was satiated. Owners also filled out a similar, detailed questionnaire regarding the cat’s pre-feeding and post-feeding behaviors at 4 and 8 weeks after the cat had been placed on a diet. Cats were weighed at initial baseline and at 4 and 8 weeks after the diet was started.

There was no significant difference in age or sex among dietary groups. Most of the cats lost weight during the first 4 weeks of the study, but there was no significant difference among the different dietary groups. After 8 weeks, cats being fed the HiFi diet lost more weight than those eating the low-carbohydrate/high-protein diet. As all diets were equicaloric, subjects on the HiFi diet were fed almost twice as much of this diet by volume than those receiving the other two diets. The fiber in the diet delays gastric emptying and therefore delays release of the peptide ghrelin, an endogenous appetite stimulant. The fiber component of the HiFi diet is cellulose, which is not digested by cats.

At 8 weeks, those cats receiving the control weight maintenance diet did not experience a significantly different amount of weight loss from the cats receiving the other two diets. Of the cats for whom data were available at 8 weeks, 38 of 50 cats (76%) had lost weight.

Pre-feeding appetitive behaviors evaluated were begging, following, meowing, and pacing. Post-feeding behaviors that were analyzed were jumping in owner’s lap, purring, resting, sleeping, and using the litter box. Many of the cats, regardless of the diet fed, did increase their appetitive behaviors in response to calorie restriction. The cats started begging behavior 16-45 minutes before feeding for all three time-points in the study. Once the diet was initiated, there was significantly more purring, sitting in owner’s lap, resting, and use of the litterbox after meals at either 4 or 8 weeks, or both. Aggression toward the owner in the dieting cats increased in only 2 of 41 cats. No cats demonstrated any house-soiling.

Results of this study should reassure both owners and veterinarians that cats actually become more affectionate when food intake is restricted, and will not exhibit undesirable behaviors. Even in the case of pre-feeding begging behaviors, most of the study owners felt that the begging behavior was affectionate. In the study, not only was the cats’ caloric intake restricted, but the feeding protocol was changed from free choice, which is how most overweight cats are fed, to meal feeding. During the study, there was also no difference in the behaviors of cats who had previously been fed ad libitum and those that had already been on a restricted diet prior to enrollment in the study.

Interestingly, there are also behavioral differences between owners of overweight cats and owners of normal-weight cats. Over half (53%) of owners of overweight cats watch their pets eating, while only 25% of owners of normal weight cats do this. Owners of overweight cats tend to view feeding as their cat’s favorite interaction with them, rather than play or petting. [PJS]