What is diabetes mellitus?
Diabetes mellitus (DM) is one of the more common endocrine (or hormonal) diseases diagnosed in dogs, particularly dogs in the 7–10-year age group. Female dogs are approximately twice as likely to be diagnosed with DM than male dogs. Diabetes mellitus is characterised by increased blood sugar or glucose levels (hyperglycaemia) resulting from insufficient secretion of insulin by the pancreas, inadequate action of insulin, or a combination of the two.
Different types of DM have been described in humans. The most common form in dogs, however, typically resembles type 1 DM in people, so the discussion below will focus mostly on this. Type 1 DM is defined as being a permanent inadequate secretion of insulin. This insulin deficiency (or hypoinsulinaemia) necessitates the administration of insulin (injectable medication) in order to manage blood sugar levels and avoid potentially life-threatening complications such as diabetic ketoacidosis that can arise if high blood sugar levels persist. This is why type 1 DM was previously known as insulin-dependent diabetes mellitus or IDDM.
Why does it occur?
Various underlying mechanisms have been identified that can contribute to the development of diabetes mellitus, these include:
Genetics
Environmental factors (for instance, overfeeding leading to obesity)
Pancreatic disease (e.g., pancreatitis)
Immune-mediated disease involving the pancreas
Disease processes (e.g., an infection) or the use of particular drugs (e.g., steroids) leading to insulin resistance
Overfeeding is often 'practised' by allowing ad libitum feeding in certain dogs - where having dry food continually available typically fosters continued grazing and eating in excess of daily requirements. Feeding excessive treats is another common cause, promoting obesity.
In many cases, a combination of the above ultimately leads to a dog developing diabetes mellitus. Certain breeds of dogs are also more likely to develop an autoimmune condition that leads to the destruction of beta cells in the pancreas and, ultimately, decreased insulin production.
Unlike the case in humans (and even in cats), where obesity-induced insulin resistance is a common cause for the development of diabetes mellitus, this has yet to be documented in dogs. That being said, overweight or obese dogs still suffer from insulin resistance, which can affect blood glucose control.
What are the more common causes of insulin resistance in dogs?
Below is a list (not exhaustive) of conditions in dogs that can lead to insulin resistance and contribute to the development of DM:
Hyperadrenocorticism (Cushing’s disease)
Dioestrus (phase of the ovarian cycle that follows oestrous) or pregnancy in females
Infection (e.g., urinary tract infection)
Pancreatitis
Obesity
Hypothyroidism
Heart disease
Chronic kidney disease
When it comes to drugs that can cause insulin resistance, the two biggest culprits are progestagens (e.g., progesterone) and corticosteroids (e.g., prednisone/prednisolone).
What are the clinical signs of diabetes in dogs?
The first four signs listed below are considered the hallmarks of diabetes mellitus in dogs.
Increased thirst or water intake (polydipsia)
Increased urination (polyuria)
Increased appetite (polyphagia)
Weight loss (despite having a healthy appetite)
Cataracts (cloudy or white appearance in both eyes)
Frequent urination (pollakiuria) +/- difficulty urinating (dysuria) and even discoloured or foul-smelling urine due to a secondary urinary tract infection
If an increased appetite is not present at the time of diagnosis, and clinical signs of nausea and/or vomiting are present, this should raise suspicion for concurrent disease processes (e.g., pancreatitis) leading to the development of DM or further consequences or complications of DM itself, such as diabetic ketoacidosis.
It’s worth noting that approximately 80% of diabetic dogs will develop cataracts within the first year of being diagnosed with the disease.
How is it diagnosed?
History and clinical signs consistent with those listed above help to create an ‘index of suspicion’ for diabetes mellitus and should prompt further testing. A diagnosis of DM is confirmed by identifying high blood sugar levels (hyperglycaemia) in conjunction with the presence of glucose in the urine (glucosuria), with the latter always considered abnormal.
With pancreatic disease known to be a potential cause of DM, an abdominal ultrasound is often also recommended at the time of diagnosis to assess the pancreas and the need for further supportive treatment.
How do we treat a diabetic dog?
As the previous name for type 1 DM implies – treating this form of diabetes mellitus is centred on administration of insulin. Various forms of insulin have been used to treat diabetic dogs. A potential complication of insulin administration is low blood glucose (hypoglycaemia) and clinical signs suggestive of this might include:
While, of course, insulin is important, consistency is key when it comes to managing any dog with diabetes mellitus. And this consistency applies to every aspect of their management. Diabetic dogs require regular insulin injections (twice daily, 12 hours apart), a fixed feeding schedule (shortly before insulin injections, twice daily, with a consistent diet), preventing or controlling other disease processes or drug administration that can lead to insulin resistance and controlled exercise at the same time each day (and avoiding strenuous exercise).
It is important to understand that treatment of a dog with diabetes mellitus does not equate to cure of the disease. In fact, the best way to describe successful treatment is control of the clinical signs that led to the diagnosis of DM. This ‘control’ can better be defined as:
Eliminating or significantly reducing the level of increased urination (polyuria)
Acceptable (i.e., avoiding obesity or being severely underweight) and stable body weight
Tolerable appetite (i.e., not ravenous)
Understanding the goal of control from the outset is crucial to managing expectations and understanding the quality of life for pet parents and dogs with diabetes mellitus.
What role does nutrition play in the management of canine diabetes mellitus?
When it comes to nutrition for diabetic dogs, the food that they are offered should be palatable, complete and balanced, and consistent in nature. This consistency applies to composition, ingredients, and caloric density.
One of the first goals when it comes to feeding a diabetic dog is to achieve (as close as possible) the estimated ideal weight for the dog in question.
In terms of diet selection, diets traditionally recommended are high in complex carbohydrates, lower in fat and contain moderate to high (insoluble) fibre. An example of a diet that meets these goals is Hill's Prescription Diet w/d. However, some studies have demonstrated that moderate carbohydrate, high fibre diets do not improve glycaemic control, compared with lower carbohydrate, moderate fibre diets (Fleeman et al. 2009).
It is well-established that the amount of starch in the diet determines postprandial (or after a meal) blood glucose in healthy dogs, with higher starch diets increasing postprandial blood glucose. There is also research that shows that the source of the starch may also affect blood glucose - in healthy dogs, barley and sorghum affect blood glucose less than corn, rice and wheat. Simple sugars are definitely not desirable in diets used for diabetic dogs. Too much of these and diabetic dogs will have marked postprandial hyperglycaemia.
The type and amount of fibre in the diet can certainly affect postprandial blood glucose and glycaemic control; research shows that gel-forming fibres like psyllium husk or guar gum can be effective at binding glucose in the intestine and moderating its absorption. However, it is important to remember that too much fibre can affect palatability and may also cause unwelcome changes in stool consistency.
The fat content of the diet offered is also something to bear in mind in dogs with diabetes mellitus. Because diabetic dogs often have accompanying pancreatitis and/or disturbances in their metabolism of lipids (i.e., fats), fat restriction might be necessary and is dependent on the findings of the initial work-up of a dog diagnosed with diabetes mellitus. Adequate, high quality protein is also important because poorly controlled diabetes can result in protein catabolism and loss of muscle mass.
To summarise, there is some ongoing debate regarding the best approach and it is certainly true that diabetic dogs can be well-managed on different types of diets.
Our approach is to formulate low carbohydrate, moderate fibre recipes for our patients, as we have found this results in improved glycaemic control.
Commercial diets like Royal Canin Diabetic are also moderate to low in carbohydrate, and enriched with different types of fibre. Remember to avoid giving high carbohydrate treats (or preferably any treats between meals).
However, the presence of comorbidities, in other words, other disease conditions, may take priority when it comes to diet selection – the best example of this would be a diabetic dog that also has chronic kidney disease. The nutritional goals for managing chronic kidney disease may take preference over those for diabetes mellitus, although, so long as the diet is kept consistent, this should have minimal impact on the overall management of such a diabetic dog.
Any other tips and tricks for managing a dog with diabetes mellitus?
Keep insulin in the fridge.
Administer the insulin injection either with food or immediately after so that the act of injecting is associated with the pleasurable experience of eating a meal.
For picky eaters – consider discussing more palatable diet options with your attending veterinarian. If the fibre content is affecting palatability, perhaps it might be worth trialling (after a slow transition) an alternative diet, like one with lower fibre. Other things that you can try to encourage dogs with a selective appetite to eat the food on offer is the addition of a meat broth or even small amounts of protein (e.g., lean minced meat) to the meal.
Always have a glucose source on hand to manage possible hypoglycaemia (low blood sugar) that could be observed during physical activity.
Keep things consistent, consistently!