Diet and Diabetes

Chapter 46


Diet and Diabetes



Diabetes mellitus in dogs and cats is a complex, multifactorial disease that develops secondary to a relative or absolute insulin deficiency or a dysfunctional response to insulin. The disease affecting dogs is primarily one of absolute insulin deficiency that occurs as a result of the complete loss of insulin production, most commonly caused by immune-mediated destruction of pancreatic β cells. The disease in cats is quite different and is similar to insulin-resistant (type 2) diabetes associated with chronic hyperglycemia, hyperinsulinemia, and obesity-induced insulin resistance that is seen in adult humans. Nevertheless, the end result in both forms of diabetes is persistent hyperglycemia and a relative or absolute lack of insulin that ultimately leads to abnormal lipid and protein metabolism that creates a catabolic state sometimes termed starvation in the face of plenty.


Insulin therapy is the mainstay of treatment for both diabetic dogs and cats (see Chapters 44 and 48), but because diabetes is a disease of disordered metabolism, nutritional therapy is a key component of the management of these patients. Although different mechanisms for development of diabetes exist for dogs and cats, concurrent pancreatitis or other conditions (e.g., obesity) may be important factors for both species that influence the nutritional plan. The general goals of dietary therapy in any diabetic dog or cat are broad based and include the following:



Although more studies (especially in cats) have been forthcoming in recent years, well-designed dietary studies in diabetic dogs and cats remain sparse, and dietary recommendations cannot be based solely on research. In addition, there are important differences between dogs and cats in dietary management strategies for this disease. This chapter reviews the most relevant aspects of nutritional management of diabetes, the major differences between dogs and cats, and the role of specific nutrients in the management of diabetes.



Dietary Management of Canine Diabetes Mellitus


Dogs with diabetes typically are presented for examination because of polyuria, polydipsia, polyphagia, or weight loss; many diabetic dogs have a thin body condition at the time of diagnosis. The goal of achieving optimal body condition in a diabetic dog requires a dietary strategy that not only assists in the control of postprandial glycemia but also allows the dog to regain its normal body weight (BW). Alternatively, some diabetic dogs are obese or have a normal body condition; in these dogs, the dietary strategy is still focused on achieving optimal body condition, but the type and amount of diet may differ from the diet for a dog that is very thin and needs to gain weight. No single dietary strategy works for all diabetic dogs; clinicians must tailor their dietary recommendations to fit the specific needs of the individual dog.



Dietary Fiber


For many years, diets containing increased amounts of dietary fiber have been recommended for dogs with diabetes because such diets may improve postprandial glycemia, presumably by delaying gastric emptying, slowing carbohydrate digestion and absorption, and altering gut hormones. No standards are set for what is considered to be high versus low fiber, just generally agreed-on ranges. Generally, high fiber is assumed to be greater than 15% dry matter (similar to many weight-loss diets); medium fiber, 5% to 15% dry matter; and low fiber, less than 5% dry matter. In addition, the term “dietary fiber” encompasses a wide variety of complex carbohydrates that have widely varying effects in the gastrointestinal (GI) tract. It is necessary to understand how dietary fiber is characterized and how these qualities affect glycemic control in diabetic dogs.


Dietary fiber is characterized by its degree of solubility, which also generally reflects both its degree of fermentability (i.e., how completely the intestinal bacteria can break it down) and its properties in water (e.g., intestinal juice). Highly soluble fibers, such as guar gum, have a great water-holding capacity and form a viscous gel-like solution in the lumen of the intestine. Conversely, insoluble fibers, such as cellulose, increase bulk and reduce intestinal transit time (i.e., increase speed of transit of ingesta through the small intestine), making nutrients (including starch) less available for digestion. In normal dogs fed diets high in soluble fibers, more rapid glucose absorption occurs because of increased intestinal glucose transport, glucagon-like peptide-1, and insulin secretion. However, it is unknown whether these same effects occur in diabetic dogs.


In studies comparing the effects of diets with soluble, insoluble, or mixed fiber in dogs with diabetes, there was no significant difference between the effects of diets on oral glucose tolerance testing; serum triglyceride levels; or the cholesterol content of high-density lipoproteins, low-density lipoproteins, or very-low-density lipoproteins. The only significant difference created by the diets was that total serum cholesterol concentrations were lower in dogs fed the diets containing mixed fiber.


Additional studies in diabetic dogs suggest that diets high in insoluble or mixed fiber may be associated with improved glycemic control. Insoluble-fiber diets appear to exert little physiologic effect on the canine GI tract compared with soluble-fiber diets and are not fermented by the bacterial flora; higher concentrations of these fibers may be added to diets with fewer side effects (e.g., diarrhea, flatulence). In other studies comparing a mixed-fiber diet with a lower fiber maintenance diet, diabetic dogs had significantly improved glycemic control when fed the mixed-fiber diet. However, regardless of the type or concentration of fiber added to the diet or the duration of time over which the diabetic dogs were monitored, there ultimately was no significant difference in the daily insulin requirement or fasting triglyceride levels.


Finally, there is a highly variable difference between dogs in their response to dietary fiber—in other words, there does not appear to be a uniform effect of fiber in all diabetics, and the effect of a type or amount of fiber in a diabetic dog is unpredictable. An investigation in diabetic dogs comparing a canned, high-fiber, moderate-starch diet with a diet that contained a moderate amount of fiber and starch found no significant difference between the diets in insulin requirements or glycemic response. The decision to use a diet with increased dietary fiber in the therapy of a diabetic dog should be based on individual circumstances because there is no clear indication that these diets are beneficial in all cases. For example, in dogs that may need to lose weight or dogs with poor glycemic control with a normal maintenance diet, diets containing increased insoluble or mixed fiber may be a reasonable choice. Alternatively, if the dog does not tolerate or refuses to eat a diet with increased amounts of fiber, the clinician should choose a maintenance or weight-loss diet containing lower fat and high complex carbohydrates. Table 46-1 lists different diets, both fiber-containing veterinary diets and non–fiber-containing diets, that may be considered for use in diabetic dogs (this is not an exhaustive list).




Dietary Carbohydrates, Fat, and Protein


The glycemic index classifies food based on its potential to increase blood glucose after absorption from the GI tract. To create diets that result in a lower, less prolonged postprandial blood glucose concentration, the glycemic index of the type of starch ingested can be considered when choosing a diet for a diabetic dog. In healthy dogs, the amount of starch in the diet is a major determinant of the glycemic index, no matter what type of dog food is tested. In one study of healthy dogs, rice-based diets resulted in significantly higher postprandial glucose levels, whereas sorghum-based diets (especially barley) resulted in the lowest glycemic response. However, predicting the glycemic index of food is based not only on the type of starch present in a diet but also on the matrix in which the carbohydrate is found, the type of processing the carbohydrate has undergone, and the total amount of carbohydrate consumed. Data about the responses of diabetic dogs to different diets and different types of carbohydrates are sparse, and it is difficult to make specific evidence-based recommendations for dogs with diabetes. However, because highly digestible diets designed for GI disease often contain rice-based carbohydrate sources, these diets may not be ideally suited for diabetic dogs.


Diabetic dogs also have abnormalities in lipid metabolism secondary to the lack of insulin production, including hypertriglyceridemia; hypercholesterolemia; and increases in lipoproteins, chylomicrons, and free fatty acids. In contrast to humans, who have increased risk of cardiovascular disease and stroke secondary to hypertriglyceridemia, the major consequence in dogs is the increased risk of pancreatitis, which complicates the management of diabetes and increases the risk for secondary complications and morbidity (see Chapters 58 and 137). In most diabetic dogs, the lipid values improve with the administration of insulin and feeding a diet containing lower fat and higher fiber content. Current recommendations by nutritionists suggest feeding a diet that contains less than 30% of metabolizable energy from fat; however, there are very few published data on the influence of dietary fat or the optimal level of fat in dogs with diabetes.


In humans with diabetes, supplementation with omega-3 fatty acids has been recommended to reduce serum lipid levels, blood pressure, and platelet aggregation—all benefits that are important to reduce the risk of stroke and cardiovascular disease. However, in some humans with diabetes, consumption of increased amounts of omega-3 fatty acids results in increased blood glucose concentrations and an overall reduction in glycemic control. The effects of omega-3 fatty acids have not been adequately evaluated in dogs with diabetes and it is unknown whether or not these same effects occur in dogs.


Finally, l-carnitine is a conditionally essential vitamin-like nutrient that has an essential role in fatty acid metabolism. Dog with poorly controlled diabetes are prone to ketogenesis, weight loss, and altered fat metabolism—all factors that can be attenuated by improved lipid metabolism that may occur with supplementation of l-carnitine. The amount of l-carnitine that is needed to achieve this effect in diabetic dogs is unclear, but in one report 50 ppm added to a canine diet improved lipid parameters in normal dogs. l-Carnitine supplementation is not routinely recommended for diabetics, but it could be considered in a patient with complications of lipid abnormalities (e.g., pancreatitis).


Protein catabolism occurs when insulin concentrations are low or ineffective. Catabolism of muscle proteins is a protective mechanism designed to supply substrate (amino acids) that can be used for gluconeogenesis. In diabetic dogs that are unregulated, not eating well, or being fed inadequate protein in the diet, muscle proteins are used. To prevent this loss of essential tissue, it is necessary that both an adequate quality and quantity of protein be supplied in the diet. In general, diets for diabetic dogs should contain a highly digestible (85% to 90%), high-quality protein (18% to 25% on a dry-matter basis) to reduce muscle catabolism. Such diets also provide adequate protein for maintenance and repair but do not appear to increase the risk of diabetic nephropathy.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Diet and Diabetes
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