Auckland vet Alex Melrose says Kiwi cats and dogs are getting far too fat.

Dr Melrose says Australian studies show one in three cats and dogs are overweight or obese and fears the situation is similar here.

"Many Kiwis simply can't see they are harming their pets with too much food and too little exercise," he says.

Dr Melrose has been a vet for more than 14 years and practises at VetCare in Grey Lynn.

He says the most significant cause of obesity in pets is owners not spending enough time with them.

"We live in a society that is becoming increasingly time-poor and too often our pets are the ones that suffer," he says.

"Often we give them treats to compensate for not taking dogs for a proper walk."

Another problem is pets eating a diet high in fat and salt.

Dr Melrose says owners should control their pet's diet the way they would control their own.

"Generally speaking if it's bad for you, it's bad for them," he says.

"If you cut off your bacon rind because you know it's bad for you, then don't give it to your dog.

Excess weight in dogs and cats can lead to serious health problems.

Obese pets are far more likely to develop circulatory diseases, heart problems and diabetes than animals of a normal weight.

They can also lose up to two years of their life expectancy, Dr Melrose says.

Companion Animal Society president Pieter Verhoek says many people don't realise the health risks obesity can cause.

"Too often owners are unaware their pets are overweight and they have no idea what it can lead to," he says.

Dr Melrose advises owners to follow guidelines on food packets and adjust portion sizes if their pet is gaining weight.

He says a dog needs at least one hour of exercise a day.

As well as walking, he says swimming is a good way for canines to keep in shape.

Encouraging cats to play outside and distracting them from food should help to control weight.