Obesity is common in dogs and cats affecting up to 25 to 40% of adult cats and dogs in developed countries. The prevalence is even higher in dogs and cats between 5 and 10 years of age. Incidence appears to be increasing but data to back this up is lacking. Obesity is defined as an excess of body fat sufficient to contribute to disease. In human beings, this is characterised by a body weight at least 20% greater than ideal, where the excess body weight is caused by an accumulation of adipose tissue. This degree of excess body weight also seems to be relevant to canine health.