Nutrition and Diabetes Mellitus
Diabetes mellitus (DM) is a metabolic disorder that results from impaired glucose handling (lack of insulin production or lack of response to insulin) such that the animal experiences persistent hyperglycemia and glucosuria. As it is for many diseases, an essential part of therapy for DM is nutrition. This article reviews the role of nutrition in the management of dogs and cats with DM.
DOES DM AFFECT DOGS AND CATS DIFFERENTLY?
In veterinary medicine, DM is divided into 2 types, which affect dogs and cats at different frequencies. The 2 types are based on pathophysiology and risk factors, which have been more fully described in human medicine.
- Type 1 DM occurs primarily in dogs. It results from destruction of the insulin-secreting beta cells in the endocrine portion of the pancreas, as a result of either immune-mediated (presumably autoimmune) mechanisms or pancreatitis.
- Type 2 DM is more prevalent in cats and results from insulin resistance. Receptors on target cells become less responsive to insulin, requiring increased insulin synthesis and secretion to maintain euglycemia. Initially, the beta cells can compensate by secreting more and more insulin; however, over time and consistent exposure to a hyperglycemic environment, the beta cells begin to fail (beta cell burnout). This process is accompanied by amyloid deposition in the failing pancreas, and type 2 DM ensues.
In cats, a unique feature of DM is the possibility of remission (previously referred to as transient DM). Cats experiencing remission might resume a euglycemic state, such that treatment can be discontinued for some time; however, for most of these cats, the diabetic state returns. In the veterinary literature, the definition of remission is not consistent, which has caused confusion over which treatment options result in remission.
WHAT ARE THE RISK FACTORS FOR DM?
Among humans, type 2 DM has reached epidemic proportions, and the prevalence is rapidly increasing. It is estimated that by the year 2025, as many as 300 million people worldwide will have type 2 DM. Significant risk factors for type 2 DM in people center on unhealthy lifestyles, including inactivity and obesity. Similarly, for cats, inactivity and obesity are significant risk factors for DM and type 2 DM is also on the rise. As companion animals, cats’ lifestyles often reflect those of the people they live with, enabling the cats to enjoy a sedentary life with access to excess calories. Many cats are kept indoors and lack access to activity. In addition, because cats often prefer to graze—eating small amounts of food throughout the day—many people keep dry food available for their cats to consume ad libitum. This combination of a sedentary lifestyle and constant access to calorie-dense dry food contributes to obesity in cats, which can then result in the development of type 2 DM.
WHAT DIET REGIMEN SHOULD I RECOMMEND FOR MY DIABETIC PATIENTS?
After a diagnosis of DM has been made, affected dogs and cats should be fed twice a day, when they receive their insulin injection. This regimen helps ensure that the animal eats enough to use the exogenous insulin. At 4 to 8 hours after injection, when the insulin is working, the animal may have a snack; however, clients should control the animal’s calorie consumption to avoid weight gain. The daily caloric requirement, especially for overweight animals, should be divided into the requisite meals and snacks. For cats, rather than trying to change their preference for grazing (an exercise in futility), work with the client to develop an optimal feeding strategy. Most diabetic cats can do well with insulin injections and food left out for grazing. If possible, the cat’s caloric requirements should be divided into 2 meals per day and the cat should be allowed to nibble on the food throughout the day.
WHAT FOOD SHOULD I RECOMMEND FOR MY DIABETIC PATIENTS?
For dogs with DM, the optimal diet is high in insoluble fiber. This diet controls glucose absorption from the gut and minimizes postprandial hyperglycemic peaks. For optimal DM control, clients are instructed to feed and give the dog insulin twice daily. As the insulin begins to be absorbed after injection, it should allow the glucose absorbed from the food to be used or stored appropriately. A high-fiber diet also helps the dog lose weight, which can have a beneficial impact on DM control. Food choices for diabetic dogs are much less important than those for cats. For dogs, it is more important that they eat regularly than be strictly limited to certain foods.
For cats with DM, diet is much more important and can significantly affect DM control. For these obligate carnivores, the optimal diet contains 12% metabolizable energy (ME) of carbohydrates. In addition, to prevent loss of lean body mass, a high-protein diet with at least 40% ME protein is recommended. There are many prescription diets on the market that have a low carbohydrate load and are formulated especially for cats. If clients will not purchase prescription low-carbohydrate diets, they can feed nonprescription canned foods; besides being generally less calorie dense, canned cat food also tends to be lower in carbohydrates. For diabetic cats in whom DM is stable and serum blood glucose is less than 300 mg/dL, a low-carbohydrate diet may be tried initially before insulin therapy to determine if remission can be achieved. However, if diet alone does not lead to euglycemia in 2 to 4 weeks, insulin therapy should be started. Insulin therapy should also be initiated if the cat is ketotic, even if eating and drinking normally.
WHAT IF THE DIABETIC PATIENT WILL NOT EAT?
Anorexia can lead to ketosis, which is an emergency situation. Ketosis is a metabolic condition resulting from an increased concentration of ketone bodies, which cause hyperosmolality and acidosis and can lead to a rapid decline in clinical condition. Ketosis occurs when the body’s balance of insulin and glucagon is altered, either from decreased insulin or increased glucagon in the bloodstream. Because one cannot remove glucagon from the system, supplementing with insulin is the best way to reverse the abnormal insulin:glucagon ratio and treat ketosis. The rule of thumb is that ketosis indicates that the patient needs more insulin. Conversely, abrupt withdrawal of insulin can alter the insulin:glucagon ratio and result in development of ketone bodies. Therefore, if a diabetic animal will not eat, it should be given half its normal insulin dose to prevent ketosis. Doing so will usually not result in hypoglycemia. If the animal continues to not eat well, it should be taken to the veterinarian to check for ketosis, hypoglycemia, or concurrent disease.
WHAT IS THE OPTIMAL FOOD FOR THE DIABETIC ANIMAL WITH A COMORBID CONDITION?
Some DM patients have a concurrent disease and would benefit from feeding recommendations other than those for DM alone. For these patients, the food choice should be based on which disease would benefit the most from nutritional intervention.
For instance, what is the appropriate food choice for a dog with inflammatory bowel disease (IBD) and DM? For a dog with IBD, a limited-antigen or hydrolyzed diet can significantly decrease gut inflammation and may reduce or eliminate the need for medical therapy; however, for a dog with DM, a diet high in insoluble fiber is ideal for slow glucose absorption. For a dog with both of these diseases, the need to control the IBD outweighs the need to control the DM, so the dog should be fed to manage the IBD.
Another example is a cat with DM and stage 2 chronic kidney disease (CKD). Dietary therapy plays an important role in preventing progression of CKD. Therefore, although a low-carbohydrate/high-protein diet can significantly affect glucose control in diabetic cats, it is more beneficial to feed to prevent CKD progression. Therefore, a cat with these comorbidities should be fed a renal diet, and the insulin dose should be increased to compensate for lack of glucose control.
- Behrend E, Holford A, Lathan P, et al. 2018 AAHA diabetes management guidelines for dogs and cats. JAAHA 2018;54(1):1-21.
- Hamper B. Current topics in canine and feline obesity. Vet Clin North Am Small Anim Pract 2016;46(5):785-795.
- International Renal Interest Society. Guidelines on the treatment of chronic kidney disease. iris-kidney.com Accessed May 2019.
- Kimmel SE, Michel KE, Hess RS, Ward CR. Effect of dietary insoluble fiber versus dietary soluble fiber on glycemic control in dogs with naturally occurring insulin-dependent diabetes mellitus. JAVMA 2000;216:1076-1081.
- Sparkes AH, Cannon M, Church D, et al. ISFM consensus guidelines on the practical management of diabetes mellitus in cats. J Feline Med Surg 2015;17:235-250.
- Verbrugghe A, Hesta M. Cats and carbohydrates: the carnivore fantasy? Vet Sci 2017;4(4):55.