The science of pet obesity: how it affects our pets

Statistics vary depending on the study, but the Association of Pet Obesity Prevention isn’t an outlier in stating that, in the US, “59% of dogs and 61% of cats were classified as overweight or having obesity in 2022.”

And while it is tempting to think that a few extra pounds are no big deal for pets, they aren’t worried about how they look in a bathing suit after all, research continues to show that simply isn’t the case.

Being overweight or obese has significant adverse effects on the health, well-being, and lifespan of both dogs and cats.

Dr. Jennifer Coates, DVM

Let’s take a look at how too much body fat affects pets.

The role of body fat in dogs and cats

Fat is not inherently bad. In fact, dogs and cats need to have an adequate amount of fat in their diets and bodies. Adipose tissue (body fat) and other types of fat have many important roles, including:

• Storing energy

• Providing cushioning

• Reducing heat loss

• Transporting molecules

• Being structural elements in cell membranes

• Helping to conduct nerve impulses

• Regulating inflammation and metabolism

Problems arise when pets have too much body fat. In general, pets who are more than 20% over their ideal body weight are considered obese, while those who weigh 10 to 19% more than what they should are classified as overweight.

Physical health impact

Inflammation

Fat cells (adipocytes) don’t just sit there making our jeans feel too tight; they’re metabolically active and have wide-ranging effects on the whole body. Adipose tissue is part of the hormonal (endocrine) system. Fat cells secrete more than 50 types of cytokines, sometimes called adipokines, that play roles in metabolism, immune function, and the cardiovascular system.

Importantly, fat cells stimulate inflammatory cells. In many ways, obesity can be thought of as a chronic inflammatory disease that makes pets sick or worsens pre-existing health problems.

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Joints and mobility

It doesn’t take much imagination to imagine how excessive weight can stress a pet’s joints. The extra wear and tear of hauling around extra pounds can potentially lead to osteoarthritis, and make the symptoms of arthritis worse in pets who already suffer from the condition.

But the problems don’t stop there. The extra inflammation caused by being overweight or obese also increases joint pain and decreases a pet’s willingness and ability to be active. Studies have found fat-derived pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6) in the joint fluid, membranes, cartilage, and bone of patients with osteoarthritis.

Osteoarthritis isn’t the only disease tied to extra body fat that limits a pet’s mobility. Overweight and obese dogs are also at higher-than-average risk for cruciate ligament ruptures and intervertebral disk disease.

Cardiovascular challenges

In people, being overweight is a significant risk factor for heart disease, hypertension (high blood pressure), and respiratory problems. The connection isn’t quite as dramatic with pets, but it’s still there. For example, a paper published in 2017 revealed significant “alterations in cardiac structure and function” in obese dogs. Another study showed that weight loss could significantly improve the situation.

In addition, fat deposits around the chest cavity can make it harder for pets to fully expand their lungs and breathe. This can be especially problematic during anaesthesia, which may partially explain why overweight and obese pets are at higher risk for complications during anaesthesia compared to pets who are at a healthy weight.

Overweight pets with pre-existing cardiovascular or respiratory conditions often have more severe symptoms, and a more rapid worsening of their conditions, compared to pets who are at a healthy weight. Weight loss can often help. For example, losing weight is an important part of the treatment plan for obese dogs who suffer from tracheal collapse.

Metabolic disruptions

Metabolic diseases are also more common in overweight pets. Diabetes mellitus is a classic example, but there’s an interesting difference between dogs and cats. Most dogs with diabetes have Type 1 Diabetes, which is an autoimmune disease that isn’t affected by weight. But most cats develop Type 2 Diabetes, which is closely connected to being overweight or obese.

Specifically, cytokines secreted by fat cells make an obese cat’s tissues less sensitive to insulin and progressively less able to move glucose (sugar) from their bloodstream into their cells. The Cornell Feline Health Center estimates that “obese cats are up to four times more likely to develop diabetes than ideal-weight cats.”

...obese cats are up to four times more likely to develop diabetes than ideal-weight cats.

Cornell Feline Health Center

The effects of weight loss in overweight diabetic cats can be dramatic. If treatment with insulin injections and dietary modifications starts quickly enough, many cats with diabetes will go into remission once they’ve lost enough weight.

Organ function

The physical presence and metabolic activity of excessive body fat affect many organs in a pet’s body. Here are a few more notable examples:

Hepatic lipidosis in cats

When cats who are overweight stop eating, their bodies often mobilise so much fat that it overwhelms their liver, leading to hepatic lipidosis (fatty liver disease).

Pancreatitis in dogs

Being overweight is one of several risk factors for the development of pancreatitis in dogs.

Lower urinary tract disease

Overweight cats are at higher-than-average risk for feline idiopathic cystitis, a condition that makes urination difficult and painful. Female dogs who are overweight often develop a fold of skin over their vulvas that traps bacteria and can lead to recurrent urinary tract infections.

Skin problems

The damp, dark skin folds created by rolls of fat are the perfect breeding ground for bacteria that cause skin infections.

Kidney disease

Various types of kidney disease appear to be more common in overweight cats and dogs.

Cushing’s disease

Being overweight makes it more likely for dogs to develop Cushing’s Disease (hyperadrenocorticism).

Cancer

Certain types of cancer in cats and dogs (such as mammary tumors in dogs) are more common in overweight and obese individuals.

Behavioural and mental health impact

The physical health problems associated with obesity in pets are well recognised. What’s equally important, however, is how being overweight can adversely affect a pet’s behaviour and mental well-being. One study found that overweight dogs are more likely to display several “undesirable” behaviours, such as fear of the outdoors and excessive barking at strangers.

Another group of researchers found that, compared to lean dogs, obese dogs had low levels of serotonin in both their blood and in their cerebral spinal fluid. While the researchers were interested in serotonin’s effects on appetite, low levels of serotonin are also associated with depression and anxiety. Perhaps that’s why the experts at Fear Free Happy Homes say that obesity can increase a pet’s “fear, anxiety, and stress.”

The bottom line

The diseases and decreased well-being associated with obesity in pets are scary enough, but a couple of studies have taken things a step further and looked at the bottom line: lifespan. A paper published in 2002 had startling results. Forty-eight Labrador retrievers were paired with their littermates. One dog was fed 25% fewer calories than the other. The dogs in the restricted feeding group were much thinner and lived, on average, almost 2 years longer than their heavier littermates.

Similar results were seen in a study performed on pet dogs in a more real-world setting. Researchers evaluated 12 breeds, comparing the lifespans of dogs who were identified as overweight to those with a normal body condition. They found that the dogs who were at a healthy weight lived up to 2 1/2 years longer than overweight dogs of the same breed.

Obesity is a pressing issue with far-reaching consequences for our pets' health, happiness, and longevity. Talk to your veterinarian if your dog or cat is overweight. Together, you and your pet’s doctor can come up with a weight management plan that will help your furry friend live a long, happy, and healthy life.

How pet insurance can help

Diagnosing, treating, and managing obesity-related health conditions can be complicated and costly, but dog insurance and cat insurance may help! Just make sure you insure your dog when they’re young so that chronic conditions may be covered instead of being considered pre-existing conditions.

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