Obesity is the most common nutritional disease in cats. Although weight loss, by dietary caloric energy restriction, is successful in experimental studies limited information exists on success of such programs in client-owned cats with naturally-occurring obesity. Further, no information currently exists on the changes in body composition during weight loss in clinical cases.

Twelve client-owned cats, diagnosed with naturally occurring obesity, were included in this prospective clinical study. Body composition was quantified by dual-energy X-ray absorptiometry, before and after weight loss, on an individually-tailored program incorporating a dry (kibbled) or moist, high-protein diet purpose-formulated for weight loss. Five cats were fed dry food only, whilst seven cats received a combination of dried and moist diet.

Mean (±standard deviation) percentage weight loss was 27±6.8% of starting body weight, and mean rate of weight loss was 0.8±0.32%/week. Mean energy allocation required to achieve weight loss was 32±7.0 Kcal/kg of maintenance energy requirement at target weight (MERTW). Although starting energy allocation did not differ between cats fed the two diet types, the mean energy allocation and end energy allocation were both significantly lower for cats feed the combination of dried and moist diets (P<0.05). Dietary non-compliance was reported, but was low (median 0.1 Kcal/kg MERTW, range 0.0 to 5.0 Kcal/Kg). The mean composition of tissue lost was 86:13:1 (fat:lean:bone mineral content [BMC]). Lean tissue loss was positively associated with overall percentage of weight loss (simple linear regression, R2=44.2%, P=0.026).

This is the first clinical study to demonstrate body composition changes during weight loss in cats. Conventional weight loss programmes produce safe weight loss, but tissue loss may be an inevitable consequence in obese cats which have to lose significant proportions of their starting body weight.