by Melinda Fleming, DVM

Obesity is the most common nutritional problem seen by veterinarians and is a serious medical issue.  The magnitude of obesity in dogs is now considered epidemic in nature.  In fact, studies have shown that approximately 20% to 40% of dogs in the general population are obese, and nearly 50% of dogs between 5 and 10 years of age are either overweight or obese.  Because this condition predisposes the pet to the development of serious secondary diseases in addition to the exacerbation of existing health problems, its impact can be devastating.  Not only is its treatment a considerable challenge for veterinarians and their staff, it can be daunting for owners.

Obesity is defined as "a pathological condition characterized by an accumulation of fat in excess of that required for optimal body function." (Elliott)  Depending on the source, dogs are considered clinically obese if they are 15% to 20% above what would be considered their ideal weight.  Body weight and body condition scoring are currently the most common methods used by veterinarians as part of a preliminary evaluation of a dog's health.  On a scale of one to five, a score of one would indicate emaciation, three would be ideal, and five would signify obesity. 

The development of obesity occurs slowly and inconspicuously, and therein lays the danger.  Many owners do not even realize the changes taking place in their pet and since these changes are so gradual, owners may consider their dog to be normal.  There are many variables that may influence the progression to obesity.  Additionally, they may be present independently or in one or more combinations. 

The accompanying table lists some breeds that are predisposed to becoming obese.  However, it is not all-inclusive and not all dogs in these breeds will actually become obese.  Some breeds have consistently shown the propensity to develop obesity (Labrador retrievers for example), and others are being acknowledged, particularly the long-haired giant breeds. 

Spayed females are almost twice as likely to be obese as intact females, and a corresponding tendency has been noted in castrated males.  However, it is unknown if neutering at an early age has any effect on the development of obesity.

Without a doubt, the most common cause of obesity is overeating and lack of exercise which results in a critical imbalance between energy intake and energy expenditure, i.e. calories in and calories out. 

While this process may seem fundamental, it is actually very dynamic.  The combination of being overfed and not exercising results in a positive energy balance which translates to excess energy being stored as fat.  Feeding highly palatable (very flavorful) foods that have high fat and carbohydrate contents lends to the problem, as does feeding ad lib, or free choice.  Supplementing with tasty tidbits (e.g. table food) and other treats adds to the overall calorie count, a detail that is often not taken into consideration.  Another overlooked risk factor is the presence of the dog when the owner is preparing or eating food.  While feeding is one part of the equation, exercise is the other.  Little or no exercise is an inherent cause in the development of obesity.  A dog that has the opportunity for consistent physical activity is less prone to becoming obese.  "The prevalence of obesity decreases in proportion with the duration of weekly exercise." (Diez, Nguyen) 

Diabetes mellitus, hypothyroidism, and hyperadrenocorticism (Cushing's disease) have all been associated with obesity.  Additionally, obesity may actually result in the dog developing diabetes mellitus.

The continuous use of some drugs can cause increased appetite which results in obesity.  The most common classes of these drugs are corticosteroids (e.g. prednisone) and antiepileptics (e.g. phenobarbital).  Also, contraceptive treatment, particularly the use of medroxyprogesterone acetate (Depo-Provera), has been shown to cause significant weight gain.

Since more dogs are being treated as family members, owners think that the pets must feel like humans do about food.  Since eating is a social activity for people and dogs, it is considered a reward more often than a source of nutrition and energy.  Sharing food is a way of showing affection, bonding and strengthening the relationship with the dog.  It can also be used as an apology or a way to relieve the owner's guilt for leaving the dog home alone.  This behavior is termed anthropomorphism, i.e. assigning human attributes to animals.  Even though unintentional, this concept can be quite harmful.  "Owners of obese animals interpret any demand from the animal as a demand for food" (Diez, Nguyen), and interestingly, one study showed that "owners of obese dogs were often obese themselves." (Kienzle, et al.)

If there is only one dog in the household, that pet is at greater risk for developing obesity.

This disease is not just about having too much body fat.  Obesity leads to significant pathology which can affect almost every organ system in the dog.  This condition has been associated with or been the causative agent in many disease processes.  Not only does it affect the quality of the dog's life, it reduces the pet's longevity.  Some of the conditions that might affect obese pets are diabetes mellitus, skin infections, reproductive disorders, mammary tumors, urinary incontinence, and exercise intolerance.   

Health problems which already exist, such as heart and lung disease, are greatly exacerbated by obesity.  Osteoarthritis and other joint diseases (e.g. hip dysplasia) are truly problematic for the obese dog.  Not only is obesity the causative agent in many diseases and aggravates existing health conditions, it can pose serious obstacles to veterinary care.

The obese patient has decreased respiratory capacity due to the fat deposits in the chest cavity.  They also are predisposed to prolonged recovery times due to the accumulation of fat-soluble anesthetic agents throughout body fat.

Surgery times are increased, which also means that the dog is under anesthesia for a longer time than a dog of normal weight.  Obese pets are also more prone to experience post-operative complications.

Other procedures, such as auscultation, palpation, blood collection, intravenous catheter placement, and radiographic interpretation are more difficult in the obese patient.

Treatment begins with the acknowledgment by the owner that the dog is obese, and that this condition poses serious health risks.  A veterinarian must perform diagnostics to rule out or treat concurrent disease.  A medical weight loss program, (which will most likely include a prescription for a reduced calorie food, recommended feedings and amounts to be fed, exercise, etc.) must be formulated by the veterinarian.  The owner must be diligent and compliant with the regimen.  It is not advisable for the dog's regular diet to be severely restricted as this could lead to insufficient energy to meet basic metabolic requirements.  In addition, this practice could lead to failure of the diet due to the pet's constant hunger and the owner's frustration.  It could also result in loss of muscle mass.  The dog would most likely gain back any weight lost during the diet, but would probably gain back even more.  One of the most important aspects of treatment is for the owner to understand that it is vital that the social relationship that has been established with the pet regarding food must be modified.  This includes not allowing the dog to be present when the owner's food is prepared and eaten.  The dog must not receive table food, including fast food.  All parties involved must realize that obesity is a chronic disease and that successful treatment, although prolonged, is possible. 

"Obesity prevention is where we should put the greatest emphasis." (Armstrong)  Veterinarians and owners alike must acknowledge that obesity is a disease and "the fight to prevent obesity from occurring or recurring in a dog requires vigilance at all times..."

(Billery, et al.)  Having a healthy canine companion is a satisfying reward that should motivate the owner and veterinary team to accomplish this goal. 

References available on request.