Normally indoor cats get fat because they are overfed and under exercised. The obesity can cause different serious diseases like high cholesterol, diabetes and heart diseases in cats. The study on cats obesity reveals that more than half of the cats in US are obese. When your cat is also effecting the overweighing situation, you must tend your attention on the cat to reduce her weight. You can also avoid the situation before your cat gets fatty. This can be done by different ways like limiting the diet and exercising.cat-obeseSource: amusingtime.com

First of all you should feed as recommended by your veterinarian. Feed the limited and recommended quantity only. The food manufacturers make rich in taste and high calories products which cats eat more than body requirement and thus causing the obesity. As we know ages make difference and the cats requires the food according to the age and size of body, feed the cats accordingly. There must be a schedule to be followed. Unscheduled eating may lead to digestive problems and eating sleeping will cause obvious weight gain. Only food is not body requirement, give the cat plenty of water to drink.