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Updated October 14, 2021 – Turn on the television, browse the internet or listen to the radio, and stories about the obesity epidemic are everywhere. According to the Centers for Disease Control, an estimated 70% of American adults are obese or overweight, and the statistics are almost as bad for our companion animals. The Association for Companion Animal Obesity Prevention reports that, according to its 2018 data, a staggering 56% of dogs and 60% of cats in the United States are overweight or obese. Obesity isn’t just a dog and cat problem; 30%-50% of horses are now considered obese, too.

Losing weight, whether for ourselves or our four-legged friends, can be a challenge and for good reason. Mounting evidence shows that body weight is regulated by a complex interplay of hormones, psychological factors, environmental influences and genetics, each contributing in some way to weight gain and loss.

Knowing more about these factors can help owners successfully manage weight loss in their companion animals.

New theories on the hows and whys of overweight companion animals

Although the basic equation of excess energy intake versus expenditure is still applicable when it comes to weight gain, other factors appear to play a role in the development and maintenance of obese or overweight body condition in our dogs. These include:


A tendency toward obesity might be inherited. Studies suggest that Labrador retrievers have the highest obesity prevalence, and recent research performed in the United Kingdom found that a genetic mutation was associated with overweight or obese Labrador retrievers as well as flat-coated retrievers. Interestingly, the mutation was more common in dogs from service dog lineages. The research team theorized dogs that were more food-motivated were easier to train as service dogs, which in turn perpetuated obesity. The team now is looking at other breeds for genetic mutations that might account for a tendency toward obesity, including using samples from the Foundation’s Golden Retriever Lifetime Study.

Breed standards

Additional studies from the Netherlands showed a strong breed predisposition in both dogs and cats toward being overweight. Researchers proposed that not only genetics, but breed standards (ideal characteristics and appearance of a breed) could explain why certain breeds tend to be overweight. In other words, certain breed standards could be linked to obesity or promote a heavier body condition. More research needs to be done in this area, but this team suggested that breed organizations scrutinize their current breed standards and adjust, as necessary.

Gut bacteria

Interest in the gut microbiota (the community of organisms residing in the gut) has exploded in the last decade in both human and veterinary medicine. Several studies have linked increased body weight to changes in the gut microbiome (the sum of all the genetic material in the gut). Veterinary researchers have documented a difference between the composition of the microbiome of obese and overweight individuals and their leaner counterparts. Studies on the cat microbiome also indicate differences between the microbiomes of obese and lean individuals. However, the question remains whether the gut bacteria change occurs prior to an animal becoming obese (and could be driving the weight gain), or changes after a dog or cat gains weight (and could possibly be perpetuating the weight gain).

Intriguing studies in mice show that giving fecal transplants from the gut of lean mice into obese mice appears to lead to weight loss in obese mice, and the opposite also appears to be true. As we learn more about the interplay between the gut microbiome and the development of obesity, the possibility of manipulating the resident microbes in the gut to assist in weight loss is a tantalizing concept. In the future, it may be possible to administer either a fecal transplant or an oral probiotic mixture to overweight animals to facilitate weight loss.

Resetting a weight thermostat?

Weight loss, whether it is in our companion animals or ourselves, is difficult to maintain. Scientists are finding that our bodies have a certain weight thermostat, and that in the face of weight loss (or even gain), our body will attempt to maintain a consistent weight. Although this effect often protects us from becoming overweight, the thermostat can get reset to an overweight or obese condition, impacting our ability to achieve or maintain weight loss. Learning how to set the thermostat to maintain a leaner body type is the subject of ongoing study in people and ultimately could help our companion animals as well.

Many factors beyond diet contribute to obesity in companion animals

It’s no surprise many factors contribute to obesity. For example, a study published in 2010 looked at environmental risk factors associated with canine obesity. Researchers found that increasing owner age, decreased weekly exercise hours, and lower owner income levels were all associated with a higher risk for companion animal obesity. The researchers concluded that in their study, owner-related factors were more important in the development of obesity than dog-related factors such as breed, age or reproductive status.

Studies show many owners underestimate body condition in their companion animals (dogs, cats and horses), leading to the misperception that their companion animals have a normal body condition when they’re actually overweight. The good news here is there are several validated body condition charts that are easy for veterinarians and owners to use. Many veterinary clinics now include this evaluation as part of their physical examination and often share these resources with clients to help them recognize when weight in their companion animal is becoming a problem.

Companion animal owners contribute to the overweight/obesity problem in other ways, too. A survey conducted from owners of obese and overweight dogs in the United Kingdom showed that dog owners had a variety of justifications for their dog’s body conditions, including the use of food to show affection, preferring that their companion animal was happy even if it meant a shorter life, and denial that their dog was overweight at all. Changing attitudes and behaviors can be a high hurdle for a veterinary team.

Veterinarians are uncomfortable talking about weight issues with clients

Discussing weight loss with companion animal owners can be difficult and a recent review on how to effectively talk to owners about weight loss indicates it makes veterinarians feel uncomfortable. The review noted that veterinarians feel that they will “offend, upset, anger, or even lose a client,” if they bring up the subject of a companion animal’s weight. If the owner or the veterinarian is overweight, the situation is even more strained. No wonder many veterinarians avoid even discussing the subject with their clients!

The same review suggested enlisting the entire veterinary team to deliver consistent and clear messaging regarding weight loss. They found that keys to successful weight loss include continuous, active engagement with owners, and tailoring weight-loss strategies to fit both the companion animal and owner’s lifestyles.

Companion animal weight loss programs fail for many reasons

Weight-loss programs fail for companion animals for many reasons. Attitudes toward companion animal feeding and even body conformation assessment can influence whether a companion animal owner adheres to a companion animal’s weight loss program, or even recognizes a need for weight loss.

Adhering to a weight loss plan can be challenging for owners. A study recently demonstrated that in a group of obese dogs referred to a weight loss program, approximately 32% dropped out before reaching their weight loss goals. The researchers couldn’t pinpoint a single cause for the dogs’ failure rate, but commonly cited reasons for dropping out included difficulty adhering to weight loss plans, lack of ongoing support and development of other illnesses that shifted the owner’s focus.

Another interesting project was originally designed as a weight loss and feeding strategy study, but the study team found something else. The researchers divided the test subjects (dogs in this case) into three groups, each assigned different diet strategies: feeding a high-fiber diet on demand; feeding a high-fiber diet that required the owners to measure out food portions; and feeding a pre-portioned combination of canned and dry food. Although there were no differences in weight loss between the groups, the researchers were surprised to find that owners were most dissatisfied when they had to measure the food portions themselves. They reported greater hunger in their companion animals and noted accompanying behavioral changes (such as increased vocalization). The team concluded that convenience and related owner perceptions of hunger behaviors could influence compliance when instituting a weight loss program.

Strategies to improve weight loss success

Obesity remains one of the few diseases that companion animal owners can influence, but it’s a journey that can take many months. Maintaining weight loss requires vigilance.

Switching a dog or cat to a prescription diet that promotes weight loss remains one of the best and easiest ways to help a companion animal lose weight. Although many commercial foods are advertised as weight-reduction or light diets, these products often are not as effective as prescription diets in promoting weight loss. The downside is prescription diets require a veterinarian’s recommendation and are almost always more expensive than diets purchased in most companion animal food stores.

One study conducted with dog owners in the United Kingdom compared prescription-diet fed exclusively and a regular commercial diet plus treats. The researchers found that costs were roughly similar when they looked at the average spent. However, there was a wide range in costs per dog, with some food costs much lower than prescription diet and some food costs much higher. This study’s finding is important because it demonstrated that at least in some cases, feeding the prescription diet was less expensive than commercial food.

Other weight-loss strategies for dogs and cats include:

  • Giving companion animals plenty of exercise and social stimulation.
  • Using food puzzles for feeding – they slow consumption while providing stimulation.
  • Thoughtful timing of spaying and neutering.
  • Using a consistent measuring device (measuring cup or scale) to determine portions.
  • Avoiding high-calorie (especially high-fat) treats, even in small amounts.
  • Enlisting the support of the entire veterinary care team.
  • Avoiding assigning blame and engaging everyone in the family to help.
  • Being patient – weight loss is hard!

More resources

To learn more about obesity, genetics and nutrition in dogs, take a peek at the June 2021 episode of Golden Zoomies featuring geneticist Dr. Eleanor Raffin and veterinary nutritionist Dr. Marge Chandler.

For additional information about obesity in cats and dogs, take a deeper dive with Dr. Chandler on our Fresh Scoop podcast.

To learn more about obesity in horses, listen to our Fresh Scoop podcast featuring Dr. Patricia Harris, specialist in veterinary and comparative nutrition. In this episode, Dr. Harris discusses the equine obesity epidemic and how to determine a horse’s body condition. Dr. Harris also offers advice for owners on how to help their horse lose weight, as well as strategies to prevent obesity.

And don’t forget that it’s important to talk to your veterinarian before starting any weight loss and exercise program for your dog, cat or horse. Your veterinarian can help guide the program and provide resources to ensure success!