Body weight decline is widespread among cats older than 11 years. A large number of such cats do not show obvious signs of illness. Digestibility data from a large population of cats maintained in different colonies showed that approximately 30% of cats older than 11 years had an impaired ability to digest nutrients, more specifically fat and protein. There is a significant negative correlation between age and nutrient digestibility in senior cats. Decreased digestibility of nutrients over the long term may lead to negative energy and nitrogen balance. This may contribute to loss in body weight and lean body mass. Data also shows that reduction in digestibility may lead to a significant decline in circulating levels of critical nutrients such as vitamins E and B12. It is important to monitor body weight of senior cats. If weight loss is observed, it is critical to provide highly palatable, digestible, energy-dense food.