As more and more Americans struggle with obesity, it looks like man's best friend also has been packing on the pounds.

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"It is kind of mirroring what is going on in our society, and it is and can be a serious health problem," Peter Falk, a veterinarian and partner at the Ocean County Veterinary Hospital, says.

A British animal welfare group said pet obesity often happens when a domestic diet is intermixed with table scraps, treats and leftovers. The People's Dispensary for Sick Animals said consuming these types of foods is toxic to our pets and can cause serious health issues. The group claims levels of pet obesity are rising.

So how do veterinary health professionals judge a dog or cat's weight and whether it is healthy?

"When we do a physical exam, we actually give the dog a 'body condition score,'" Falk said. On a scale of 1 to 9 — 1 being very, very skinny and 9 being severely obese — a score of 5 is considered average.

According to Falk, overweight dogs and cats are subject to the same health risks as humans, including heart, lung and liver problems. A pet that is overweight is more likely to have arthritis, diabetes, heart problems and other internal issues.

If you look down on your dog or cat, you should be able to see their waist.

"If dogs stay the ideal weight or even a little less, they have probably a longer lifespan by an average of one to two years," Falk said. "And the onset of the diseases that I mentioned would be markedly reduced. Carrying a lot of extra weight is a big deal."

But at home with your dog or cat, how can you make a sound and proper weight judgment?

Falk said if you look down on your dog or cat, you should be able to see their waist, and you should be able to feel their ribs, but not see them.

"When it comes to feeding pets, less is more," he said. "Use your veterinarian as a guide for what would be nutritionally appropriate for your pet based on size, breed -- dog, cat -- and age."