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.