Many veterinarians feel that feline obesity is increasing in prevalence within Japan, but are unsure as to what real rate of obesity prevalence exists currently. The objectives of this study are twofold. First, we sought to determine the ratio of overweight/obese cats, as determined via body condition score (BCS), based on a cross-sectional pool of healthy cats. Second, using a uniform method of biochemical measurement for cat plasma collected all over Japan, we sought to construct cross-sectional working reference ranges of plasma metabolites using age, BCS, and sex as classifying factors. Overall, the rate of overweight and obese cats (BCS of >3) was 56%, whereas obese cats (BCS >4) constituted 42% of our pool. Aging leads to an increased risk of developing lipid metabolism and kidney issues. Increases in BCS and age both carry increased risk of insulin resistance development. Moreover, increases in BCS bring about a higher risk of developing lipid metabolism problems, which may lead to the development of high cholesterol and triglyceride lipidemia, accompanied by higher levels of free fatty acids. Males appear to have a higher risk than females of developing higher BCS and body weight values, in addition to higher insulin and lower adiponectin values.