Obesity is not just a growing health problem among humans, it seems.
Half of dogs and cats in the UK are now overweight, according to the RSPCA.
TV vet Joe Inglis, who has teamed up with the charity to launch a Pets Get Slim website and roadshow tomorrow, said that "action needs to be taken" over pet obesity.
"Whether your pet is obese or slightly overweight - it matters. A weight problem can affect a pet's quality of life and lead to straining of the joints, causing arthritis, as well as internal illnesses like diabetes, liver disease and heart disease," he said.
"Pet obesity is not an issue to be taken lightly - with so many overweight pets, action needs to be taken today."
He said the website, petsgetslim.co.uk, would give pet owners help and motivation to keep their pets on a diet.
"We know diets are difficult and when you've got a pet begging for treats with pleading eyes, it's really tough," he added.
On the site, pet owners can upload photos of their pets, share weight loss experiences and be voted "pet slimmer of the week".
At Pets Get Slim roadshows, to be held in Southampton, Bristol, Cardiff, Birmingham and Manchester this week, visitors can have their animals weighed and discover their pet's ideal weight.
The RSPCA said it hoped through the roadshow to further assess the problem of pet obesity, which can also increase skin problems and the risk of fatty tumours.
The charity said that if you could not easily feel a dog or cat's ribs, it probably meant it was overweight.
A study by the University of Edinburgh earlier this month showed that one in 230 cats in the UK were now diabetic, with overweight cats over three times more likely to suffer from the condition.
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