Wild animals don't have to make a New Year's resolution to go on a diet.

"We used to laugh when I was in vet school and say, there aren't any fat wolves," says Denver veterinarian Kevin Fitzgerald, of Animal Planet's "Emergency Vets" and "E-Vet Interns."

Unfortunately for those of us living more domesticated lives - no matter the species - weight is no laughing matter. As more Americans struggle with obesity, there's an unsurprising result for the pets sitting on the couch with us. About a third of American pets are overweight, according to some studies.

"Sadly, our companion animals reflect our lifestyle. If you're sedentary, there's a pretty good chance your dog is sedentary too," Fitzgerald says.

Carrying too much weight affects the health of nearly every system of the body - joints, heart, respiratory system, even skin - as well your pet's lifespan. But the good news is that, unlike many other health issues, this is one where you can make a real difference.

For pets, just like for people, the solution is simple, if not always easy: burn more, eat less. Fortunately, your dog or cat can't work the can opener, or get into the fridge for a midnight snack. You're in control, and it's important to have the whole family on board.

Fitzgerald says the first step is a basic one: measure your pet's food. He advises pet owners to use a measuring cup when doling out food, unlike some of his clients. "They'll say "Oh, I'm doing a cup" - and it's not a cup, it's a coffee can!"

Fitzgerald emphasizes that this goes for cats too. "Feeding free-choice for cats is a big problem. Put the food down for 30 minutes twice a day and pick it up."

You don't have to totally eliminate treats - just include them in the day's measure of food. "There are tricks," Fitzgerald says. "Break the biscuit into thirds." After all, what dog wouldn't rather think he was getting three cookies instead of one?

Your vet can help you decide the correct amount to feed, and may be able to recommend a reduced-calorie food. And it's important to consult with your vet about cats, who are subject to potentially fatal fatty liver syndrome if they lose weight too fast.

Fitzgerald also says that while diet is primary, inactivity is part of the problem for our indoor pets. "A lot of cats are apartment dwellers - they don't get any exercise. We've taken a hunter, stalker species and made them couch potatoes."

Playing with your pets more will help burn more calories, but don't suddenly start taking your dog on marathons, since extra weight and its associated health problems can affect the ability to exercise. "Talk to your vet about your dogs' overall condition and how much is realistic," he says.

And remember that you're in it for the long haul - you won't see results overnight. "I see that the people are psyched - for two months they do a great job, and six months later they're back to the same weight."

It's a long-term commitment. But you owe it to your pets, because it's all up to you.