Diabetes mellitus is a common endocrine disease in dogs and cats. It occurs primarily due to secretory dysfunction of the pancreatic beta cell, and is associated with multiple risk factors, including genetic predisposition, physical inactivity, increased age and obesity. Cats appear to have a disease bearing similarities to type 2 diabetes in humans, resulting from beta cell dysfunction and peripheral insulin resistance.
Current estimates suggest a prevalence of diabetes mellitus of between 1:100 to 1:500 (Sparkes et al., 2015). However, this has been increasing with the rise in obesity in both species, with animals in excessive body condition almost four times more likely to have the disease (Brito-Casillas et al., 2016).
When well managed, the prognosis for affected individuals can be very good. Studies in cats have shown median survival times of between 13 and 29 months (Sparkes et al., 2015). In dogs, a median survival of 24 months has been reported, with 33 percent of dogs surviving more than three years (Callegari et al., 2013).
In addition to insulin therapy and regular exercise, diet is a key factor in the management of the condition.
The role of the diet
Weight gain is associated with insulin resistance; therefore, the first goal of dietary therapy should be to normalise body weight in obese patients, while providing adequate nutrition. A weight loss goal in obese cats of 0.5 to 2 percent reduction in weight per week, and in dogs of 1 to 2 percent reduction per week, is advised until the ideal body weight is reached.
For both species, dietary therapy should minimise the demand on beta cells to produce insulin, normalise body weight and muscle mass, reduce postprandial hyperglycaemia and minimise fluctuations in blood glucose.
Management in dogs
Meals should be timed at 12-hour intervals to coincide with insulin administration, ensuring that maximal exogenous insulin activity occurs during the postprandial period. Each meal should contain half the daily caloric requirement. Regular and consistent exercise is recommended.
Fat
Fat should comprise less than 30 percent of metabolisable energy (ME). This is particularly important in dogs with concurrent hyperadrenocorticism or chronic pancreatitis. If the fasting serum triglyceride concentration is not well controlled, then further dietary fat restriction (less than 20 percent) may be indicated.
Complex carbohydrates
Complex carbohydrates (CH) should comprise less than 30 percent of ME. A diet high in insoluble dietary fibre (30 to 40g/1000kcal; diets containing approximately 12 percent insoluble fibre are likely to be most effective) improves glycaemic control and lowers mean pre/postprandial blood glucose, compared to diets containing either very low concentrations of total dietary fibre, or high concentrations of soluble dietary fibre. Insoluble fibre forms a viscous gel in the intestine, impairing the absorption of glucose from the gut lumen, thus decreasing postprandial blood glucose fluctuations.
Complications of excessive fibre include increased frequency of defecation, constipation (psyllium or canned pumpkin can be added to soften the stool), watery stools, flatulence (an insoluble fibre diet can be added and the quantity of the soluble fibre diet decreased) and refusal to eat the diet.
Proteins
Proteins should comprise greater than 30 percent of ME. As both CH and fat are usually restricted in diets formulated for diabetic dogs, dietary protein will provide a substantial source of calories.
Obese dogs fed a diet high in insoluble dietary fibre and protein with a low-fat content achieve more rapid weight loss than dogs fed a similar diet with only moderate fibre content (Rand et al., 2013). In underweight dogs, the principal goal is also to normalise body weight by increasing muscle mass and stabilising insulin requirements. A high-quality, calorie-dense maintenance diet with lower fibre content may be fed to these dogs.
Management in cats
In contrast to dogs, the primary goal of therapy in cats should be to achieve diabetic remission; this is achievable in 80 percent of newly diagnosed cats (Rand et al., 2013).
A further difference compared to dogs is that the timing of meals need not be so closely matched to insulin administration, as the duration of postprandial glycaemia in cats is markedly longer than in dogs. Exercise can be increased via hiding food in several areas in the house or using a treat dispenser (Figure 1).
Fat
The diet should be moderate to low fat (containing less than 4g/100 kcal).
Complex carbohydrates
CH should be low – less than 12 percent of ME and less than 3g/100kcal. A complex CH source with a low glycaemic index (eg whole grains such as barley) should be fed. Novel CH sources (lentil, tapioca) have been associated with no postprandial increase in blood glucose (Rand et al., 2013). For cats already receiving insulin therapy, changing to a low CH diet should be accompanied by an insulin dose reduction of 30 to 50 percent (Rand et al., 2013).
Proteins
Proteins should comprise greater than 40 percent of ME and greater than 10g/100kcal. Protein is essential to replace lost muscle mass, prevent hepatic lipidosis and increase metabolism to promote weight loss and normal insulin function. If dietary protein is restricted, CH will usually be increased to maintain an adequate calorie content.
Benet et al. (2015) concluded that diabetic cats were significantly more likely to revert to a non-insulin dependent state when they were fed with low CH tinned food.
70 percent of diabetic cats are either overweight or obese (Rand et al., 2013). Feeding exclusively wet food may help with weight loss, as this tends to result in reduced calorie consumption, improve satiety and increase total water intake. These diets also delay glucose absorption from the intestinal lumen. In obese cats, the caloric intake should be limited to 70 percent of maintenance requirements.
Underweight cats and those already in ideal body condition require a high-quality, calorie-dense, low CH diet that is palatable, with the amount of food adjusted to maintain ideal body condition.
In inappetant cats, the first priority is to offer any food they will eat to avoid development of hepatic lipidosis. Dietary changes should be implemented when the cat is eating readily, and introduced gradually over a period of 7 to 10 days. In cats diagnosed more than two to three years previously or with concurrent disease, the probability of remission is low, so the goal of therapy should be to control the clinical signs associated with the disease.
Diabetes mellitus can be well managed with insulin therapy, an appropriate diet and cooperation from the owner. Selection of a specific diet (Table 1) should be based on individual requirements.
A full reference list is available on request
