Chapter 57


Prevalence and Risk Factors

The incidence of obesity is reaching epidemic proportions worldwide, and the impact of excessive body fat on overall health is a topic at the forefront of human medicine. Obesity in companion animals has similar health consequences and should receive the same attention from practitioners as other chronic diseases. In dogs and cats a general definition for obesity is exceeding ideal body weight by 15% to 20% because of excess adipose tissue. Based on recent studies, approximately 35% to 40% and 25% to 35% of adult dogs and cats, respectively, are either overweight or obese.

Several risk factors are linked to obesity in dogs and cats. In both species the peak incidence occurs at middle age and is often associated with gonadectomy. Several studies in cats suggest that weight gain after spaying or neutering is a combination of slower metabolic rate and increased food intake. The metabolic changes caused by gonadectomy in dogs are not clear, but increased food consumption and decreased activity levels are suggested mechanisms for weight gain. Gender can also influence weight gain, with spayed female dogs and neutered male cats having an increased risk for excess body fat. Breed also plays a significant role in the development of obesity in dogs. In particular, the golden retriever, dachshund, Shetland sheepdog, Labrador retriever, cocker spaniel, and dalmatian are more likely to become overweight. Finally, environmental factors such as sedentary lifestyles and ad libitum feeding regimens contribute to both canine and feline obesity.


Weight gain occurs when energy intake exceeds energy output. Certain diseases such as hypothyroidism and Cushing’s disease can contribute to weight gain by decreasing the metabolic rate and energy output. However, most overweight dogs and cats do not have underlying endocrine disease, and weight gain is caused by excessive caloric intake with inadequate physical activity.

Until recently, adipose tissue was thought to be involved only in energy storage and insulation. The role of adipose tissue as an endocrine organ is now established, and hormones and proteins secreted from adipose cells, termed adipokines, have roles in appetite, inflammation, insulin sensitivity, and metabolism. To date, over 100 adipokines have been identified; some of the most intensely studied ones are leptin, adiponectin, and tumor necrosis factor-α (TNF-α). Leptin was the first adipokine identified and its main function is to regulate body fat mass through appetite and energy metabolism. As adipose tissue increases, more leptin is secreted from adipocytes. Leptin inhibits neurotransmitters that increase appetite and slow metabolism and stimulates neurons that decrease appetite and increase energy expenditure. Therefore, as individuals gain body fat, leptin promotes weight loss. Adiponectin is the most abundantly secreted adipokine in circulation. Although adipocytes are responsible for secreting adiponectin, hormone levels become paradoxically lower with increased fat mass. Adiponectin is closely associated with insulin sensitivity, independent of body fat mass. Numerous clinical and epidemiologic studies in humans associate low levels of adiponectin with chronic inflammatory states such as obesity, insulin resistance, type 2 diabetes mellitus, and cardiovascular disease. Therefore, as individuals gain weight, they have lower concentrations of adiponectin and higher disease risk. While initial adiponectin studies in cats demonstrate characteristics similar to those for humans, canine studies are variable and further research is needed. TNF-α is an inflammatory cytokine expressed by many cell types including macrophages, adipocytes, mast cells, neuronal cells, and fibroblasts. Obesity increases macrophage migration into adipose tissue, causing increased TNF-α expression in overweight individuals. One theory behind recruitment of monocytes and macrophages to expanding adipose tissue is that increased levels of adipocyte apoptosis and necrosis produce chemoattractant agents. One of the primary actions of adipose TNF-α is induction of local insulin resistance. In addition to inhibiting glucose entry into cells, TNF-α decreases uptake of free fatty acids (FFA) into adipocytes and promotes lipolysis and release of FFA into circulation. As a result, FFA levels increase in circulation and negatively affect insulin sensitivity in peripheral tissues.

Obesity affects systemic health not only by releasing adipokines but also through mechanical compression of organs and excessive strain on joints. Obesity has also been implicated in the cause or progression of neoplasia, cardiorespiratory disease, urogenital disease, endocrinopathies, metabolic derangements, dermatologic disease, and orthopedic disorders (Box 57-1).

Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Obesity

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