Obesity in dogs, Part 1: Exploring the causes and consequences of canine obesity - Veterinary Medicine
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Obesity in dogs, Part 1: Exploring the causes and consequences of canine obesity
This increasingly common condition decreases a dog's life span, increases its risk for various cancers, and causes orthopedic problems—just to name a few of the possible sequelae.


VETERINARY MEDICINE


CONSEQUENCES OF OBESITY


Table 2: Potential Consequences of Overweight or Obesity in Dogs
It is generally well-known that obesity has many consequences in people. We are now beginning to recognize the many potential consequences obesity has in dogs, as well (Table 2).

Longevity

As in people, obesity adversely impacts longevity in dogs. In one study in which 24 pairs of Labrador retrievers were randomly assigned to an ad libitum feeding group or an energy-restricted group (fed 75% of the amount consumed by the respective pair mate), the energy-restricted group's BCS was closer to the optimal score than the ad libitum feeding group's BCS was.46 The energy-restricted animals lived 1.8 years longer, had improved glucose tolerance (body fat mass and insulin resistance were correlated—the threshold range for increased insulin resistance was 5,000 g of body fat—energy-restricted dogs had lower body fat composition), and had reduced risk of orthopedic disorders such as osteoarthritis.

Endocrine disease

Diabetes mellitus and hypothyroidism are frequently associated with canine obesity. In people, tissues develop insulin resistance with excessive caloric intake. Plasma concentrations of insulin also increase in direct proportion to increasing BMI in men and women. Abdominal obesity is a major determinant of insulin resistance, hyperinsulinemia, and, subsequently, type-2 diabetes mellitus in people.10,47,48 In people, metabolic syndrome is a group of risk factors associated with insulin resistance, cardiovascular disease, and inflammation.4,49 Canine diabetic patients commonly suffer from diabetes mellitus resembling human type-1 diabetes mellitus. Since type-2 diabetes mellitus is uncommon in dogs, obesity rarely leads to overt clinical signs of diabetes mellitus.46

Although hypothyroidism is commonly considered an underlying cause of obesity, such cases are relatively unusual.50 While hypothyroidism should always be a differential diagnosis in obese dogs, it is rarely the sole cause. Obese dogs have marginally higher concentrations of both total T4 and total T3 concentrations than nonobese dogs do, but free T4 concentrations, thyroid stimulating hormone (TSH) concentrations, and TSH stimulation test results are not significantly different.51,52 Thus, although obesity may have some effect on thyroid homeostasis, such changes are unlikely to affect the interpretation of thyroid function tests.

Hyperadrenocorticism has been associated with increased intra-abdominal adipose deposition. Combined with the weakening of ventral abdominal musculature secondary to endogenous corticosteroids, patients living with this condition certainly may be readily classified as overweight or obese.53,54

Dyslipidemia

In experimental models, obese dogs had mild elevations in cholesterol, triglyceride, and phospholipid concentrations compared with normal-weight dogs.29,55 Laboratory dogs that had been made obese had increased total cholesterol concentrations and increased cholesterol concentrations in very-low-density lipoprotein (VLDL), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) fractions. Additionally, these dogs had higher triglyceride concentrations in total plasma and in the VLDL fractions. These dyslipidemic changes were associated with insulin resistance after lipid infusion.29,55

Orthopedic disorders

Orthopedic diseases, including osteoarthritis, osteochondrosis, and osteochondritis dissecans, are the most common obesity-associated problems in dogs.56,57 A recent study demonstrated food intake may have a significant effect on the development of osteoarthritis in dogs, and the disease severity was associated with unrestricted feeding.58

Cardiopulmonary disease and hypertension

Obesity may have a marked effect on respiratory function and is a recognized risk factor for the development of tracheal collapse in small-breed dogs.59 Other respiratory diseases frequently exacerbated by obesity include laryngeal paralysis, asthma, and brachycephalic airway obstruction syndrome; obstruction of thoracic movement related to obesity hypoventilation syndrome (also known as Pickwickian-type syndrome) also occurs.60-63 Obesity hypoventilation syndrome in people is defined as obesity accompanied by lethargy, drowsiness, hypoventilation, hypoxia, and secondary polycythemia.

Obesity may also affect arterial blood pressure in pets, as hypertension has been reported in 23% to 45% of obese dogs.12,64 One study showed that 67% of obese dogs had a systolic blood pressure > 160 mm Hg and that obese dogs had significantly higher blood pressure than control dogs did.65 Hypertension was considered a risk factor associated with BCS in dogs.

Obesity in people reduces systolic and diastolic functions of both the left and right ventricles, and the severity of the dysfunction is related to the magnitude of obesity.66-68 Research has also shown that overweight dogs without overt heart disease have preclinical left myocardial systolic and diastolic function changes.69 Thus, even without a predisposition to ischemic heart disease, obesity has an impact on ventricular function in dogs.


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Source: VETERINARY MEDICINE,
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