A growing number of domestic cats are tipping the scales at unhealthy weights. According to veterinarian Samuel Wong at North Point's Cosmo Pet Service Centre, 25 to 40 per cent of pet cats are overweight, while about 5 per cent are obese. 'Long term, obesity will affect the health of a cat,' he says. 'But rarely, will owners bring their cat to see a vet solely for its weight problem. If it's fat, but still playful, eating and happy, most people will think it's normal for a cat to be fat.' On the contrary, Wong says thin felines are usually in perfect condition. Owners should be able to feel a cat's ribs and backbone easily, not a bulging waistline. Cats with extra weight can develop a slew of problems. Everything from high-risk diabetes and joint problems (similar to dogs and humans) caused by excessive weight to hepatic lipidosis also known as fatty liver disease, and cystitis or inflammation of the bladder. For signs of potentially fatal hepatic lipidosis, watch out for a hungry cat that stops eating. Instead of using food for energy, the cat's body reverts to stored fat, which is processed by the liver. But the liver becomes overwhelmed by the amount of fat and stops working. 'This is a treatable condition, but you might need to force feed your cat with a syringe. It can be very labour intensive,' Wong explains. 'If you are working full-time the cat might need to stay in hospital and have liquid food pumped directly into the stomach.' Diabetes is another condition that can be caused by obesity. If your feline seems to be urinating more frequently, this might be the early stages of diabetes. However, most owners will probably miss this early warning sign. 'Once your cat has had diabetes for a long time, it will suddenly become sick with diabetic ketoacidosis [insufficient insulin in the body] that can kill an animal if not treated early,' Wong says. According to the vet, domestic shorthair cats are more prone to obesity, along with males, cats less than 10 years old and indoor felines. 'Ninety-nine per cent of cats are indoor pets, so they lack exercise and are confined to a small apartment. They spend most of their time sleeping and eating,' says Wong, who is also a qualified veterinary acupuncturist. 'When owners leave [the home], they put out a big bowl of food, I think to feel less guilty about leaving them alone.' The vet recommends a good quality pet food that is grain free, or a high-protein, low carbohydrate diet. 'Cats are carnivores and can live on just protein and fat, but unfortunately a lot of cat food has grains and carbs,' Wong explains. If your cat is overweight by 10 per cent, Wong suggests losing about 1 per cent of body weight per week. However, losing weight too quickly can be dangerous. He says it's best to check with a vet before starting a diet routine. 'Having a safe weight-loss programme depends on the owner and whether he or she is compliant. Many times when we put a cat on a weight-loss diet, it doesn't happen in real life, the owner is still feeding it treats and the cat hasn't lost any weight in a year.' To calculate how much you should be feeding, Wong advises owners to dish out between 50 and 80 kilocalories (kcal) per kilogram depending on the optimal weight. If your cat is on the light side, feed it a higher kcal, but for bigger cats use the lower end. It's also best to use a weight scale when measuring food. 'If you use a measuring cup, it's quite inaccurate. There could be a 20 per cent variable,' he says. Other factors that can help weight loss are toys that make the cat play more and sleep less, a climbing tree and cat perches. One of the most obvious steps would be to 'cut out unhealthy treats and snacks,' Wong says.