Overweight and obese dogs and cats are common in developed countries. In the US, for example, 34% of dogs and 35% of cats are overweight or obese. This represents 20.4 million dogs and 24.4 million cats.

An obese pet is 20% or more above its ideal weight. Obesity causes biochemical changes that result in increased susceptibility to other diseases. Recent research is offering new insights into why this is so.

Fat is dynamic

Scientists have found that fat cells are metabolically active and constitute the largest endocrine organ in the body. They secrete adipokines that affect the brain and peripheral nervous system, skeletal muscle and the liver. There are many adipokines that have numerous functions such as regulation of satiety (feeling full), carbohydrate and lipid metabolism and insulin sensitivity.

Recognizing that fat cells are not inert has shed light on the complex relationship between obesity and some of the disease associated with obesity, including:

• Heart disease;
• Diabetes;
• Joint disease;
• Skin disease; and
• Lower urinary tract disease.

The biochemical changes caused by obesity can be quantified by studying fat cell genomics.

Genomics of fat cells

New research tools such as genomics have allowed scientists to help explain the underlying mechanisms that link obesity with other diseases. A recent study looked at the effects of weight loss on the gene expression profiles of obese dogs. These dogs were fed a dry, low-fat, fiber-enhanced therapeutic food for four months. On average, the dogs lost 41.2% of their initial fat mass in that time (R. Yamka, et al ., 2008).

The nutrigenomic effect from the food was seen in the shift from an obese gene to a lean gene expression profile. Once the dogs lost weight, the genes identified showed down-regulationa "turning off" of genes associated with fat accumulation. In obese dogs fed the weight loss food, metabolism shifted to a lean genomic profile. Weight loss appears to reverse many of the ill effects caused by obesity.

Correct systemic effects

The effect of weight loss on the gene expression profile for obese cats also has been studied (P.J. Armstrong, Yakma, R., 2008). For a four-month period, cats were fed a low-fat, high-fiber, dry therapeutic food. On average, cats lost 30.7% of their initial fat mass. The nutrigenomic effect of the food was seen in the down-regulation of genes associated with inflammation, obesity and type 2 diabetes mellitus. This study supported the theory that weight loss can correct the systemic effects of obesity.

Weight loss drugs

It's been known for a long time that obesity predisposes to other diseases, but now we know more about why it does. Eventually new knowledge could lead to more drugs to promote weight loss.

One that's available now is Slentrol from Pfizer Animal Health . Slentrol is a microsomal triglyceride transfer protein (MTP) inhibitor. It works by preventing some dietary fat from being absorbed into the body. When that happens a message is sent to the brain's satiety center that signals dogs to stop eating.

Another potential drug that holds promise is leptin, a satiety hormone secreted by fat cells. It acts in the hypothalamus, a part of the brain that is responsible for coordinating many body functions, including appetite and satiety. Leptin apparently suppresses appetite, resulting in decreased food intake and weight loss.

Body condition scoring

Many pet owners don't realize their pet is overweight. The American Animal Hospital Association Pet Owner Survey reported that 17% of pet owners rated their pet as overweight, while veterinarians estimate that 44% of their patients are overweight.

Pet owners can determine if their pet is overweight by using the following body condition scoring system:

• Gently place hands on the pet's rib cage. Do the ribs seem to be covered by lots of flesh? Is it hard to even feel them?
• Is there fat on the lower back and the base of the tail?
• Does the pet have no "waist" (or only a slight one) when viewed from above?

Answering yes to one or more of these questions indicates the pet is overweight or obese.

Increasing lifespan

Obesity leads to several health problems and decreases the lifespan of pets. For many reasons, it makes sense for the petfood industry to help prevent and treat pet obesity-keeping in mind it's much easier to prevent than treat.