How Does Exercise Lower the Blood Glucose?

I recently was asked a fantastic question about how exercise lowers blood glucose levels. Exercise lowering the blood glucose is independent of insulin levels. I hadn’t really thought to explain it previously to our ADW clients. So I did a bit of reading to make sure that I really understood it myself! One of my better qualities as a veterinarian, I believe, is that I can explain complicated stuff in an understandable fashion. So, here goes:

When we eat, our bodies have the ability to store a certain amount of energy in either the liver or muscle cells. What isn’t used immediately can be stored in these tissues as glycogen, up to a certain limit anyway. Any excess beyond what is used immediately or beyond the capacity to store it as glycogen is then stored as fat.

Here’s the nifty part! The liver can turn the glycogen back into glucose if needed for use anywhere in the body. Our bodies are so clever! This is how the Somogyi swing can happen, aka rebound effect. For example, if the pet receives too much insulin which would drive the blood glucose too low, the liver can react and turn glycogen into glucose and save the day! Or, in the old fight or flight adrenaline situation, it can again turn glycogen into glucose for a pet to make a quick getaway. This is how the white coat syndrome happens and why I’m always encouraging owners of diabetic pets to do blood glucose curves at home instead of in the vet clinic setting. If a pet is stressed, this hepatogluconeogenesis, the liver making sugar from stored glycogen, can make the blood glucose level higher in the vet clinic than it might be at home where a pet is relaxed. If we veterinarians think the blood glucose is higher than it actually is on a regular day to day basis, we might incorrectly advise that a higher dose of insulin is needed.

In muscle, the glycogen cannot be turned back into glucose for elsewhere in the body, but is destined to be used by the muscle. When a pet is active, it uses up the stored glycogen and the body needs to refill those glycogen stores. That is how exercise lowers the blood glucose.

Sometimes clients ask about oral medications for diabetes. Some clients want an option besides insulin injections. Lots of type 2 diabetic humans take oral anti-hyperglycemic meds such as Metformin. Metformin works in the liver to lower the liver’s ability to turn glycogen back into glucose. Theoretically, metformin would work for type 2, non-insulin dependent, diabetic pets. In general, dogs are usually insulin dependent, type 1 diabetics. And cats usually start off as non-insulin dependent type 2 diabetics but then transition into type 1 diabetics if the situation progresses. Vets have indeed tried using oral anti-hyperglycemic medication for type 2 diabetic cats, but the longer we dawdle before getting a cat on insulin, the less likely the cat is to go into remission. Veterinarians are better off using insulin to get a cat regulated and out of so called “glucose toxicity” than to pussyfoot around trying oral meds. Furthermore, metformin can cause tummy upset or inappetence. In general, vets do not use oral anti-hyperglycemic meds on pets for these reasons.

Now you are likely asking, “What the heck is glucose toxicity?” I’ll give it to you in a nutshell. Remember that the pancreas has a hormonal function to makes insulin and a digestive function to make enzymes to break down fat. We avoid fatty foods for diabetic pets because so many diabetic pets become diabetic after an episode of pancreatitis, but I digress… This discussion is on insulin! Insulin is made in the pancreatic beta cells. When the blood glucose is elevated, it makes the beta cells cranky and dysfunctional. In the face of chronic high blood glucose, these beta cells die sooner than normal. So, not only are the beta cells the ones who are failing in insulin production in the first place, the high blood glucose causes them to deteriorate even further. This “glucose toxicity” is a known phenomenon in human diabetics and also cat diabetics. It likely it occurs in dogs as well.

This is good reason to be a conscientious pet owner and run your blood glucose curves and do all you can to have your pet’s diabetes well controlled, particularly for felines who may actually go into diabetes remission. Dr. Jacquie Rands, a veterinarian in Australia, showed that when the blood glucose in cats was over 16 mmol/L (about 290 mg/dl) the beta cell function experienced this glucose toxicity. Newly diagnosed diabetic cats can go into remission if treated promptly with insulin. This remission usually also requires a low carbohydrate, typically canned food only, diet but it can happen occasionally for cats eating dry kibble. We try to stack the odds in our favor by feeding diabetic cats low-carb food. Canned food is usually much lower in carbs than dry food. The carb content of cat foods can be found on the internet if you search for cat food composition chart.

Have a question or comment? Post below or email me at [email protected]. I always enjoy hearing from my readers!

NOTE: Consult your veterinarian first to make sure my recommendations fit your pets special health needs.