Fifi has a snacking problem. Jack can barely walk. Bobby's double chin prevents her from cleaning herself properly. And these are just three of the 18 contestants with serious weight problems in Britain's "Pet Fit Club" competition. Taking a page from the popular American weight-loss reality TV show The Biggest Loser, a U.K. veterinary charity is putting morbidly obese dogs, cats, and rabbits on a strict diet and exercise regimen to get them back to a healthy weight. (See a video below.) Here's what you should know:

How big of a problem is pet obesity?
Very big. Excess pounds may make our furry companions look extra cuddly, but they can also cause a number of serious health problems, including high blood pressure, arthritis, diabetes, and even cancer. More than one-third of British dogs and one in four cats are overweight. It's even worse here in the U.S., where more than half of adult dogs and cats are overweight or obese. 

Who is organizing this contest?
The Pet Fit Club is run by the U.K. veterinary charity People's Dispensary for Sick Animals (PDSA), and is in its seventh year. To participate in the competition, which is not televised, U.K. pet owners submitted their heavyweight furry friends, and the PDSA narrows it down to 18 of the most in-need pets. Together, the group — made up of 11 pooches, five cats, and two rabbits — tips the scale at a whopping 336 pounds.

How will the competition work?
The 18 bulging contestants, with the help of their owners, will embark on a strict six-month regimen of healthy pet food and exercise. Some pets, like Fifi, a 21-pound cat who is 107 percent overweight, will have to unlearn bad behavior like stealing food from other cats and charming unknowing neighbors into doling out free treats. A team of veterinarians and nurses oversee the program, which includes regular weigh-ins and advice for frustrated owners.

What can they win?
Come September, the dog, cat, or rabbit that loses the most weight for its size will win a year's supply of diet pet food and a two-night stay for the winner and two humans at a Four Seasons Hotel.

Sources: CNN, Daily News, The Huffington Post, MSNBC