Comparative aspects of human, canine, and feline obesity and factors predicting progression to diabetes

Obesity and diabetes mellitus are common diseases in humans, dogs and cats and their prevalence is increasing. Obesity has been clearly identified as a risk factor for type 2 diabetes in humans and cats but recent data are missing in dogs, although there is evidence that the unprecedented rise in canine obesity in the last decade has led to a rise in canine diabetes of similar magnitude. The insulin resistance of obesity has often been portrayed as major culprit in the loss of glucose control; however, insulin resistance alone is not a good indicator of progression to diabetes in people or pets. A loss of beta cell function is necessary to provide the link to impaired fasting and post-prandial plasma glucose. Increased endogenous glucose output by the liver is also a prerequisite for the increase in fasting blood glucose when non-diabetic obese humans and pets develop diabetes. This may be due to decreased hepatic insulin sensitivity, decreased insulin concentrations, or a combination of both. While inflammation is a major link between obesity and diabetes in humans, there is little evidence that a similar phenomenon exists in cats. In dogs, more studies are needed to examine this important issue.