The vast majority of cats diagnosed with diabetes mellitus have what is called Type 2 diabetes. Type 2 diabetes usually goes hand in hand with obesity, and a big factor behind this relationship is insulin resistance. The pancreas is still making sufficient amounts of insulin (responsible for helping cells absorb glucose from the blood stream), but the body becomes unable to respond to the hormone effectively.
Insulin resistance develops because adipose tissue does more than just store energy in the form of fat. It is also an endocrine organ. In other words, fat secretes hormones that significantly affect the way in which a cat’s body functions, including the way in which it responds to insulin.
The concept of insulin resistance is familiar to many cat owners, but have you heard of leptin-resistance? Until recently, I hadn’t either.
Leptin is a hormone produced by adipocytes (fat cells) that plays an important role in regulating fat storage in the body. The system is like a thermostat that monitors body fat rather than heat. Greater amounts of fat secrete greater amounts of leptin; in effect the adipocytes are trying to tell the rest of the body, “We’ve got adequate reserves here. There’s no need to keep packing on the pounds.” Leptin works in the brain by activating neurons that suppress the appetite and increase energy expenditure and inhibiting neurotransmitters that have the opposite effect. Therefore when body fat increases, higher levels of leptin work to slim the cat back down.
Leptin is one of the reasons why slender cats tend to stay that way. If they start to get a little chunky, the extra fat secretes more leptin, which helps them naturally lose what they should.
This elegant system can be overwhelmed and breaks down when cats become overweight, however. Several studies have shown that despite extremely high blood leptin concentrations, obese cats will continue to overeat and gain even more weight. Similar to what happens with insulin resistance, the leptin is there but the body can no longer respond to it. Leptin resistance is probably just one of the reasons why getting overweight cats to slim down can be so frustrating.
A reasonable question is “Can giving an obese patient additional leptin help with weight loss?” Unfortunately, studies in people have not indicated that leptin administration in these situations is effective, but cats are physiologically unique, so we can still hold out hope. As far as I am aware, no research into the use of leptin in cats has been done. In the meantime, I hope that being aware of leptin resistance and the other problems that excess body fat can wreak on the body will encourage us all to watch how much food we offer our cats.
After all, it’s easier to prevent obesity than reverse it after it has altered the very way in which a cat’s body functions.
Dr. Jennifer Coates