By Ernie Ward, DVM
During the past 20 years, I’ve heard all the clever wordplay: “Pet obesity is a huge problem!” “The number of overweight pets is growing!” “Obesity rates continue to expand!” “Weight-related medical bills are stretching pet owners’ budgets!” I’ve also witnessed the pet obesity discussion evolve from “Fat is funny!” to “Fat is dangerous!” to “Fat is boring!” Perhaps the fact that most patients we see these days are overweight or obese, many veterinarians are ignoring the serious health threats pet obesity poses. To kick off this special three-part series on pet obesity, I thought we should begin with some of the main medical reasons pet obesity is a BIG problem. And, yes, I went there in all caps.
I started the Association for Pet Obesity Prevention (APOP) in 2005 with two simple goals: one, to measure the prevalence of pet obesity in the U.S., and two, to raise pet obesity awareness among veterinary professionals and pet owners. In other words, how many pets with obesity were there and did people know about it? In 2016, APOP’s survey revealed 59 percent of cats and 54 percent of dogs were classified as overweight or obese by their veterinary clinics. That adds up to an estimated 50.5 million cats and 41.9 million dogs at risk for weight-related disorders. Obesity is relatively easy to identify but infinitely more difficult to treat.
Obesity is perhaps the most complex, challenging and, ultimately, most important medical conditions in both human and veterinary medicine. Obesity affects nearly everyone—human and animal—in some harmful manner, steals billions in medical bills and robs quality of life and life expectancy for hundreds of millions. That’s why the battle to cure obesity is so important and must be addressed during every appointment.
Ample evidence exists that excess weight and adipose (fat) tissue in dogs and cats is associated with many serious consequences. Obesity has been shown to cause or exacerbate osteoarthritis and hypertension, and is linked with several cancers. Pets with obesity are at increased risk of metabolic and endocrine disorders, especially type 2 diabetes, respiratory disorders and renal dysfunction. In my opinion, the most significant consequence of pet obesity is diminished quality of life and reduced life expectancy. Science is pointing toward chronic, low-grade inflammation as the chief common denominator of these obesity-related disorders.
Killer Chronic Inflammation
Inflammation is the new obesity. Let me explain it this way: Pet owners see a “big” pet. Most veterinarians see a “fat” pet. I see an “adipokine storm.” Adipokines? That’s code for inflammation.
Adipokines (also called adipocytokines or cytokines) are signal proteins produced by fat tissue. Leptin, adiponectin and interleukin-6 (IL-6) are examples of adipokines. We know adipokines cause or contribute to hundreds of harmful inflammatory processes throughout the body. Think of every fat cell as a little factory pumping out hundreds of potentially toxic compounds. Multiply that image by millions or billions in a pet suffering from obesity. The real danger of excess fat isn’t the fat—it’s the inflammation the fat causes. This is what I want us to communicate to clients: Inflammation is the new pet obesity. Reducing chronic systemic inflammation should be a primary objective of treatment.
Decreased Life Expectancy
Less is more when it comes to feeding pets and living longer. Eating less has been proven to extend life expectancy and reduce suffering in species as diverse as worms, spiders, water fleas, fruit flies, fish, hamsters, mice, rats, dogs and monkeys. Longevity studies in dogs have found dogs fed 25 percent fewer calories than normal and kept at a lean body mass lived an average two years longer and had fewer medical problems. The study dogs also required fewer medications and remained more active well into old age. Perhaps the fountain of youth for pets lies in the food bowl.
Most veterinarians view the relationship with between excess weight and osteoarthritis (OA) as a “wear-and- tear” process. In simplest terms, a joint is overloaded, the cartilage breaks down and, voila, arthritis. While that mechanistic pathway remains true, recent research shows the reasons pets with obesity develop OA may be more complex and insidious.
Adiponectin and leptin appear to be the key adipokines involved in OA. Other fat-derived compounds that contribute to OA in pets are tumor necrosis factor-alpha (TNFalpha), adipose angiotensinogen (AGT) and interleukin-1 beta (IL-1 beta). In a nutshell, these adipose- derived compounds can cause inflammation throughout the body, including joints. In addition to the inflammation caused by these fat-produced chemicals, OA in dogs also is worsened by oxidative stress and activation of the flow of inflammatory compounds, the arachidonic cascade, associated with obesity.
Diabetes and Insulin Resistance
Obesity is known to cause diabetes and insulin resistance in cats and dogs. In obese pets, the number of insulin receptors on the fat and muscle cells are reduced, damaged or don’t function normally. There are several proposed reasons for this, and research is underway to discover the definitive mechanism. Regardless of exact cause, pets with obesity have too few properly working insulin receptors, leading to hyperinsulinemia. Making matters worse, excess glucose is left circulating, because the abnormal receptors don’t correctly bind insulin. One theory is the insulin-secreting beta cells of the pancreas fail over time, resulting in diabetes. This is speculated to be due to prolonged and high demand on these cells to produce insulin, oxidative damage or the toxic effects of persistent high blood sugar on pancreatic beta cells.
The take-home message is the relationship among insulin, obesity and longevity is intimately intertwined. Studies show that the more efficient a dog is at removing glucose from the blood after a meal, the longer its life expectancy and the higher its quality of life. In other words, the more sensitive a dog is to insulin, as opposed to an obese dog’s lack of response to insulin, the longer it is likely to live.
High Blood Pressure
Hypertension in overweight dogs is an area of recent interest among veterinary researchers. While we still don’t fully understand the link between obesity and high blood pressure, we are closer to a more thorough understanding.
That link has been studied for more than 25 years.
Several studies have proven the link among high fat diets, obesity and hypertension, especially in dogs. Several genes and biomarkers have been proposed as indicators and a variety of triggers postulated, with little widespread consensus at present. For now, veterinarians need to communicate that pets with obesity are at increased risk for hypertension and should be screened regularly.
Based on current evidence, it’s clear excess weight in dogs and cats can lead to high blood pressure. Hypertension directly affects the kidney, largely because it receives approximately one-quarter of the blood pumped by the heart. Dogs with obesity have been shown to have higher levels of hyaluronic acid (HA) inside their kidneys. HA, a lubricant and is found mainly in the cartilage, joint fluid, skin and rear half of the eye (vitreous), is responsible for making cartilage highly resistant to compression. Incidentally, HA was referred to as a “goo” molecule until the 1970s. The accumulation of hyaluronic acid damages the kidneys and causes sodium resorption, water retention and high blood pressure. Studies are mixed on whether kidney damage from HA is completely reversible if the excess weight is lost. Additional research is needed to determine the exact extent obesity plays in kidney disease and the improvement, if any, weight loss has on obesity-related kidney disease. Preventing pet obesity is our best treatment advice for now.
Obesity can cause respiratory problems in people and pets through a variety of mechanisms. The presence of excess fat along the chest wall and abdomen compresses the spongy lungs, reducing the amount of air taken
in with each breath. In many ways, obesity is like having a heavy bag pushing down on your chest—it makes it incredibly difficult to catch your breath. This excess fat also may alter the normal breathing pattern, resulting in uneven and jerky breathing. Many dogs or cats will pant excessively after even a short walk in a desperate attempt to gain more oxygen. In pets suffering from morbid obesity may experience a ventilation- perfusion abnormality, which is basically a condition where not enough oxygen enters the body but the dog still has normal arterial carbon dioxide levels. This condition is more commonly associated with congenital heart defects. It’s hard to imagine that obesity can cause the same respiratory distress as a major birth defect.
In addition, I’m concerned that pets with obesity suffer poor restorative sleep and disrupted sleep patterns. Studies are ongoing, but as monitoring devices become more sophisticated and accessible, I expect veterinarians will be discussing obesity-related sleep disorders very soon.
For the past 30 years, the relationship between obesity and certain cancers has been growing. At least 13 types of cancer are linked to obesity in humans, including colorectal and stomach cancer, uterine, breast, ovarian and endometrial cancer in postmenopausal women, kidney, esophageal, pancreatic, thyroid and multiple myeloma. The National Cancer Institute estimates that obesity and physical inactivity may account for 25 to 30 percent of major cancers. Animal models used in cancer research and current evidence suggest dogs and cats with obesity may also be at greater risk for developing cancer.
The debate on the fat-cancer link centers on whether excess fat cells primarily promote cancer or if the obesity-related insulin- resistance is to blame. Estrogens and estrogenlike compounds, insulin and growth factors, and chronic inflammation caused by excess fat all are proven ways obesity leads to cancer. The bottom line is that obesity causes increased cancer rates, certainly in mice and men; we just don’t understand exactly how.
In my opinion and experience, obesity and its low-grade inflammation is the biggest health threat pets face. That’s a bold statement, but I’m confident based on all available evidence. The more we learn about excessive inflammation in pets, the more we understand the importance of keeping it at safe levels. Our bodies are a biological broth comprised of hormones, proteins and toxins competing for chemical reactions that create our physiological future. If we add too many adipokines from excess fat into the mix, the resultant stew can be deadly. Excess fat tissues generate inflammation. Inflammation is harmful and decreases quality of life in pets. Do a little research, and next month I’ll tackle tactfully talking about obesity with pet owners.
Dr. Ernie Ward has spent his entire career practicing, writing about, teaching and encouraging better care for animals to earn the title as America’s Pet Advocate. Whether he’s discussing the dangers of obesity, how to perform a physical examination, dealing with behavioral issues, answering pet owner’s questions about nutrition or surgery, or innovating better care for aging pets, his unifying theme is: Do what is in the pet’s best interest.