It's not just people in America who are overweight, but our pets too, with the Association for Pet Obesity Prevention estimating that some 60 percent of pet cats in the U.S. are overweight, as are 56 percent of dogs. The total number of overweight or obese dogs and cats is estimated to be 100 million, up from 80 million just five years ago. Making the problem worse is that many pet owners don't realize that it's a health problem, just as it is for humans, viewing their pets' extra pudge as cute. Some pets are genetically vulnerable to putting on extra pounds or may have a disease causing them to gain weight. As with humans, aging slows down metabolism, and neutering or spaying an animal decreases its energy needs. But veterinarians say the main culprit in pets weighing too much is overfeeding, particularly letting them have easy access to food around the house and overindulgence in high-calorie treats. Stress may also play a role -- but not necessarily the animal's stress. Dr. Deborah Linder, head of Tufts University’s obesity clinic for animals, told the New York Times that stressed owners may stress-feed their pets. She said, "Pets don’t open the fridge by themselves. The concept of food and love are tightly interconnected, and we need to address it."