A number of different medical conditions may be the cause of your cat’s weight gain. See your vet for further advice. Find your nearest vet.
Your cat may be supplementing its diet from next door or from the wild. Whatever the cause cats normally regulate their diet.
In many cases it can be due to reduced activity. This could be caused by an environment which is poor in toys, climbing areas, or play sessions. This can lead to increased resting or feigned sleep, see low activity.
Ultimately the cat may be suffering from stress. This can be quite subtle in cats. When it is associated to insufficient exercise it can lead to obesity. This in turn can lead to other major health problems like heart disease, osteoarthritis and diabetes.
Over-eating may also be the result of competition between cats in the home. This can lead a cat to eat faster and more every time they have access to their food bowl before being chased away. For more on see conflict between cats.
Provide exercise (climbing opportunities, toys, and play sessions).
Monitor your cat's food intake if it is tending to put on excess weight.
Change for a low calorie diet (in addition to keeping control of the total daily quantity provided) and continue to monitor your cat’s weight.
Plug in a Feliway Diffuser in the room your cat spends most of its time for at least 30 days, and replace refills as required. Some cats may benefit from permanent use of pheromones.
If weight gain continues, take your cat to a vet to make sure that the problem isn't being caused by a medical issue.
Give each cat in your household its own separate eating or drinking area to avoid stress caused by sharing its food or water with other cats. Spread them in different locations, which can mean separate rooms/floors, or at least having one bowl in high place compared to another on the floor in another part of the room.
See how to make a Cat friendly home.
For even more information go to the International Cat Care section on Obesity in Cats.
* image provided by N Massal