Has your cat been moving more slowly, sleeping more than usual and losing interest in play time? It's not uncommon for pets—or their owners—but if your feline friend has become overweight, you might need to put it on a diet.

Vicki Jo Harrison, president of the International Cat Association (TICA), told Newsweek that a cat is at risk of developing "serious medical conditions" if it is just 2 pounds above its ideal body weight.

Zazie Todd, author of Purr: The Science of Making Your Cat Happy, also described obesity as "a growing problem for cats."

The health problems suffered by overweight cats include:

Below, vets and other cat health specialists explain how and when to put your cat on a diet.

Dr. Bruce Kornreich, director of the Feline Health Center at Cornell University's College of Veterinary Medicine, told Newsweek that a cat can be given a body condition score.

This "semi-subjective" scoring system is based on attributes such as the ability to see and feel the cat's ribs or the bones of their spine, as well as the presence of a waist or "abdominal fat pad."

The most commonly used scale ranges from 1 to 9, with 1 signifying "emaciated" and 9 "extremely obese." An ideal score on this scale is a 5, Kornreich said. "The body condition score is best used in consultation with a veterinarian."

Each cat has an ideal weight for its size and breed, Harrison said. You can find more information about this data at the TICA website.

A cat is considered overweight when it weighs 10 to 20 percent more than its ideal body weight, explain Dr. Krista Williams and Dr. Robin Downing in an article on the website of animal hospital chain VCA. A cat is obese if it weighs 20 percent or more above the ideal.

Harrison listed nine signs that your cat is overweight:

Another indicator that your cat needs a diet change is that it cannot groom some areas of its body properly because it can no longer reach them, according to Kornreich.

Diseases more likely to occur in overweight cats or ones that are made more difficult to treat in these cats include diabetes mellitus (a disease of the pancreas) and osteoarthritis. These can also indicate your cat should go on a diet, he said.

Pam Johnson-Bennett, a cat behavior expert and author of Think Like a Cat, told Newsweek: "Cats are carnivores so a healthy diet must include protein from animal sources."

Kornreich suggested consulting a veterinarian and/or veterinary nutritionist to ensure the cat food you buy provides "a nutritionally complete and balanced diet."

"Proprietary cat foods that are nutritionally complete and balanced for the life stage of a cat—kitten versus adult—will have a label from the American Association of Feed Control Officials on their packaging stating this," he explained.

Talking to the vet is especially important for cats that need a specific diet to address a health concern—such as to dissolve urinary stones, limit carbohydrates if they're diabetic or avoid proteins that cause allergic reactions—Kornreich added.

He also warned against raw diets for cats. "Some of these may contain pathogens like bacteria and/or parasites that may be harmful to cats and their owners."

Harrison, Johnson-Bennett and Todd all advised cat owners to consult their veterinarian to create a safe weight loss program.

A veterinarian can work out an appropriate amount of weight loss for your cat and how many calories it needs each day.

Once the veterinarian has determined that your cat should lose weight, "the development of a feeding program to promote weight loss must be undertaken very carefully," Kornreich said.

This plan can be developed around the diet the cat is already following, he added. But in some cases, specialized weight-loss diets may be recommended.

Kornreich also suggested that cat owners try the Cornell Feline Health Center's app, which allows users to generate and track the progress of a feeding plan designed to "safely promote weight loss in overweight cats using proprietary foods of their choice." The iOS app should be used in consultation with a veterinarian, he added.

There can be "serious medical issues" if a cat shed pounds too quickly, Todd warned. Johnson-Bennett pointed out that drastic diets can put cats at risk of hepatic lipidosis, a serious liver condition.

Underfed cats are prone to this condition, Kornreich explained, during which "fats are mobilized and accumulate inside the liver cells, negatively impacting their myriad vital functions."

Hepatic lipidosis can be fatal or cause severe illness, so owners must seek guidance from a veterinary professional if their cat needs to lose weight.

"Cats should not lose more than between 0.5 and 2 percent of their body weight per week," he said. "Owners of overweight cats should understand that it can take significant amounts of time—commonly many months to over a year—for a cat to achieve an ideal weight."

Johnson-Bennett recommended incorporating puzzle feeders into the daily routine of cats that are on diets. These food-dispensing toys must be physically manipulated by the cat in order to retrieve an edible reward.

"Puzzle feeders are great for cats who eat too quickly or have difficulty waiting for the next scheduled meal" as well as providing increased activity, she said.

Harrison suggested starting a cat's weight-loss program by "cutting out all treats and tidbits," including milk, for two weeks.

It's also a good idea to divide your cat's food into smaller, more frequent meals to help manage their hunger, said Harrison. "Just make sure you keep track of what, and how much, you're feeding," she added.

Johnson-Bennett also recommended this technique, pointing out that this is how cats would "naturally eat in a free-range environment, as small predators who hunt small prey."

After the first two weeks of the diet, check your cat's body condition and continue the diet until they've reached their ideal weight, advised Harrison.

"Once your cat has reached their perfect shape and size, you can look at slightly adjusting their feeding quantities to stabilize their weight for the future," she said.

Remember that "it's not just increased feedings and treats that impact your cat's weight," said Harrison. "A lack of exercise can add extra pounds."

Johnson-Bennett pointed out that cats, like their owners, will do better if their healthy diet is combined with physical activity. "Luckily for cats, exercise can come in the form of fun through increased playtime."

Here are some ways to keep your cat active, suggested by Harrison and Johnson-Bennett:

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