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    If your pooch is paunchy or your feline looks, well, fat, he might be more than just pleasantly plump. According to a recent study by the Veterinary Pet Insurance Company, pets' waistlines are expanding as rapidly as their owners': Nearly 40% of our nation's animal companions are obese.

    RELATED: How to Tell if Your Pet is Overweight

    "Obesity in animals--as in people--can cause a lot of problems, such as diabetes and arthritis, later in life," says Jack Walther, DVM, president of the American Veterinary Medical Association. If your beloved pet is tipping the scales into the unhealthy range, here is a three-step plan for getting him back into shape.

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    1. Assess Your Pet's Girth

    "Owners spend so much time with their pets, they often don't recognize that their dogs or cats are overweight," says Kathryn Michel, DVM, an assistant professor of nutrition at the University of Pennsylvania School of Veterinary Medicine. "But they need to determine the optimal body condition for their specific pets." To do so, she recommends doing a rib check on dogs, similar to pinching an inch on our own waistlines: Place your thumbs on your canine's spine and let your fingers hang down. You should be able to easily discern each of your dog's ribs under a thin layer of fat as you glide your fingers along the torso. If you can't find them, it's time to trim down.

    And though some people think a Garfield-size gut on a cat is cute, abdominal fat is actually a sign that your kitty is too heavy. "On a cat, a rib check is deceiving," says Michel. "Instead, look for 'fat pads' underneath the belly. If you can see them, your cat needs to lose weight." Finally, just as humans have waists, so do animals. "Dogs and cats should have indentations on their sides when you look at them from a top view," says Dan Christian, DVM, executive director of the Purina Pet Institute.

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    2. Know His Nutritional Needs

    "One of the biggest mistakes owners make is leaving a bowl of food sitting around the entire day," says Walther. "A pet can graze as he pleases and consequently get overfed." Instead, ask your vet how much food your pet actually needs on a daily basis (or, at the very least, read the pet-food label) and divide this serving into two, feeding your pooch or cat half in the morning and half at night. And try putting your cat's bowl on a countertop, washing machine, or other elevated surface. Lazy kitties will have to jump up to reach it, a bit of extra exercise that might also dissuade them from nonstop munching throughout the day. If you opt for a low-calorie meal option, check with your vet first to make sure it meets your pet's nutritional needs.

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    3. Get Him Moving

    Dogs and cats need more exercise than many owners realize. "Most people think that walking a dog for 15 minutes a day will do the trick, but we recommend a minimum of three 20-minute exercise sessions a day," says Christian. These can include walking, ball throwing, Frisbee fetching, even gnawing a rawhide-anything that gets your hound off the couch and burning calories.

    RELATED: 10 New Ways to Exercise With Your Pet

    Exercising your cat can be a little trickier. One suggestion: Purchase a "kitty-tease," a fishing rod-like toy with a feather or other item attached to the end. Your cat will swipe at, jump on, and chase down the feather to his heart's delight. If your kitty is nocturnal (many cats are), be sure to throw him a ball or a toy for a few minutes each evening.

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    Next: 12 Secret Home Remedies For Dogs and Cats

    4. Healthy Rewards

    High-fiber fruits or vegetables (such as carrots) will fill up a dog's tummy without tacking on pounds.

    Many people assume that canned cat food is high in calories, but just the opposite is true. To reward your feline for good behavior, give her 1 teaspoon of her favorite wet food. It's tasty and rich in protein.

    If you must give treats, choose the diet kind found in pet stores. Calories are listed on the bag so you won't be tempted to go over your pet's daily ration.