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From Veterinary Quarterly Review, Texas A&M University

Pet obesity is a serious problem in the U.S. In 2006, the largest and oldest provider of pet insurance, Veterinary Pet Insurance (VPI), paid more than $14 million in claims linked to obesity, which was seven percent of all medical claims submitted to VPI. Studies suggest that 25 to 40 percent of all pets in the U.S. are overweight. Veterinarians have long known that obesity is harmful to pets and is associated with diseases like pancreatitis, hypertension, diabetes, asthma, hepatitis, lipomas and others. However, new knowledge is shedding light on how fat cells in obese pets over stimulate the appetite and make the affected animal miserable.

A dog is obese when it weighs 20 percent more than its estimated normal body weight or has a body condition score of 8/9 or 9/9. A recent study showed neutered pets requires 25 percent fewer calories than non-neutered animals after reaching mature body size. Since most pets are

neutered, it is much easier for pets to become obese. At birth, mammals have all the fat cells they will ever have with one major exception: when an animal’s fat cells are already full and the animal continues to consume more energy than required, these fat cells will divide. The animal then has extra fat cells that never go away unless surgically removed. Since the discovery in 1994 that fat cells secrete leptin, which causes appetite satiation (among other things), it is now known fat cells are even more endocrine-like because they secrete many other substances like cortisone (which increases appetite) and cytokines like prostaglandins, IL-6 and TNF alpha.

Obesity causes a vicious cycle of potentially harmful events. In obese animals, the normal actions of leptin to decrease appetite and increase energy rate are blocked, resulting in a state of leptin resistance (or leptin inactivity). The appetite stays the same or increases. At the same time, pro-inflammatory cytokines from fat cells cause long-term damage to organ systems and tissue, like joints. The overall effect is the life span and quality of life in obese pets tends to be reduced.