Giving your pet a small piece of cheese is like giving them a hamburger and pet owners need to resist the urge, vets say.
About a third of New Zealand's cats and dogs are overweight or obese, and vets are calling for pet owners to check their animal's weight on Wednesday's Pet Obesity Awareness Day.
New Zealand Veterinary Association spokeswoman Dr Liza Schneider said it was up to owners to make sure they did not feed pets calorie full, nutrient-poor food.
"We think we are loving our pets by piling their plates high and giving them lots of treats but instead we are paving the way to a life of ill health or even an early death," she said.
Overweight pets could develop osteoarthritis and joint pain, cardiac and respiratory conditions, diabetes and are a greater surgery risk.
Even 25 grams of cheese contains enough calories to represent one and a half hamburgers for a dog and two and a half hamburgers for a cat.
While a dog's food intake is straightforward to monitor, cats are "picky eaters", Dr Schneider said.
"If you are not feeding them what they want they will often visit the neighbour and make their hunger known.
"If this is the case, perhaps a quiet word to your neighbours to resist your feline's charms will help."
She recommended supplementing a pet's diet with Omega 3 fatty acids to help burn excess fat.