What to Feed Diabetic Dogs: An Evidence-Based Approach

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What to Feed Diabetic Dogs: An Evidence-Based Approach
ACVIM 2003
Linda M Fleeman, BVSc, MACVSc
Brisbane, Australia

GENERAL GOALS OF NUTRITIONAL THERAPY FOR CANINE DIABETES

Evidence based on expert opinion, clinical experience, and pathophysiological rationale

The food fed to diabetic dogs should provide adequate calories to achieve and maintain optimal body condition. Dogs with poorly controlled diabetes have a decreased ability to metabolize the nutrients absorbed from their gastrointestinal tract and lose glucose in their urine, so require more calories for maintenance than healthy dogs. The diet fed should be nutritionally balanced and needs to be palatable so that food intake is predictable. Meals should ideally be timed so that maximal exogenous insulin activity occurs during the postprandial period.1 Because the daily insulin-dosing regimen tends to be fixed for diabetic dogs, it is also important that a predictable glycemic response is achieved following each meal. Consequently, every meal should contain roughly the same ingredients and calorie content, and should be fed at the same times each day. The owners of diabetic dogs should be aware that a consistent insulin-dosing and feeding routine is optimal.

DIETARY FIBER AND CANINE DIABETES

Evidence based on pathophysiological rationale and a randomized, controlled trial in non-diabetic dogs

Dietary fiber can be characterized by degree of solubility, which is a reflection of its properties in an aqueous media. Soluble fiber has great water-holding capacity, forms a viscous solution in water, and is readily degraded by colonic microflora in dogs to produce short-chain fatty acids that are absorbed across the intestinal mucosa. Dogs fed diets with increased viscosity may have more rapid postprandial glucose absorption, resulting in higher total postprandial glucose absorption, and are more likely to develop secretary diarrhea than dogs fed diets with lower viscosity.2 This suggests that only diets with an intermediate viscosity level may be associated with a delay in gastrointestinal transit time and optimal glucose homeostasis in dogs. Dogs cannot digest the insoluble fiber component of their diet and it is excreted in the feces. In contrast to soluble fiber, insoluble fiber seems to exert relatively little physiological effect in the canine gut and can be tolerated in fairly high dietary levels.3

Dietary fiber can be characterized by degree of fermentability, as well as solubility. Fermentable dietary fiber is associated with increased intestinal glucose transport capacity, increased glucagon-like-peptide-1, and increased insulin secretion in non-diabetic dogs.4 The overall effect is a significant reduction of area under the blood glucose concentration versus time curve during oral glucose tolerance testing. As diabetic dogs lack the capacity to increase insulin secretion and match increased intestinal glucose transport, it needs to be investigated whether they benefit from diets containing high levels of fermentable fiber or whether these diets may contribute to glucose intolerance.

Randomized, controlled evaluation in non-diabetic dogs of the effects of diets containing different fiber types (highly-soluble, highly-fermentable guar gum, poorly-soluble, poorly-fermentable cellulose, and mixed soluble-insoluble, moderately-fermentable sugar beet fiber) at three different dietary concentrations has helped to clarify some of the issues relating to the putative glucoregulatory effects of dietary fiber in dogs.5 Compared with control diets, there were no significant differences in physical findings, serum glucose and insulin concentrations during oral glucose tolerance testing, serum triglyceride concentrations, or cholesterol content of HDL, LDL, and VLDL associated with feeding any of the fiber-modified diets. The only significant findings were that total serum cholesterol concentrations were lower in dogs fed sugar beet fiber and higher in dogs fed cellulose fiber, compared with control diets. Although it was not objectively measured, it was noted that the dogs' hair coats seemed to become dull and lusterless when they consumed the fiber-modified diets. The authors proposed that this might have been due to an inhibitory effect of fiber on the absorption of minerals and vitamins.

Evidence based on various clinical trials in diabetic dogs

Studies in diabetic dogs indicate that high-fiber diets may be associated with improved glycemic control.6-11 When dogs were fed a single meal containing increased soluble fiber or increased insoluble fiber, a greater reduction of postprandial hyperglycemia was seen with the meal containing soluble fiber.6 However, when comparison was made following long-term feeding of diets high in soluble fiber or insoluble fiber for 1or2months7,10, a tendency for improved glycemic control and fewer side effects was seen with the diets containing increased insoluble fiber. In particular, significantly lower glycosylated hemoglobin7 or fructosamine10 levels were recorded. A diet containing a blend of soluble and insoluble fibers resulted in significantly improved glycemic control in a group of diabetic dogs that had previously been fed commercial dog food supplemented with bread or biscuit.11 Regardless of the composition of the high-fiber diet or the length of time over which the dogs are monitored, no significant difference in daily insulin requirement7-12 or fasting triglyceride7,9,11 between groups of diabetic dogs fed low-fiber and high-fiber diets has been found. Glycemic control is statistically similar when diabetic dogs are fed diets containing different quantities of fiber and different fiber sources, although results suggest that soy fiber might be preferable to cellulose in moderate-fiber diets.12

Importantly, there seems to be marked variation between the responses of individual diabetic dogs to dietary fiber. In one study9, significant improvement of all indices of glycemic control, including lowered daily insulin requirement, was seen in 9 of 11 dogs when they were fed a high-fiber diet. The remaining 2 dogs were found to have improved glycemic control on the low-fiber diet. In another study of 12diabetic dogs12, glycemic control was best in 6dogs when fed a soy-based, moderate-fiber diet, in 4dogs when fed a cellulose-based, high-fiber diet, in 1dog when fed a cellulose-based, moderate-fiber diet, and glycemic response to diet could not be ranked in the remaining dog. A similar situation exists for people because high-fiber diets do not have a uniform effect in all diabetic subjects.13 This may be partly due to the side effects that are sometimes associated with high-fiber diets, which include poor palatability, poor weight gain, poor hair coat, vomiting, voluminous feces, flatulence, diarrhea, and constipation.

Evidence based on a randomized, controlled clinical trial in diabetic dogs

A randomized, controlled trial was performed to assess the influence of canned, high-fiber, moderate-starch diets on insulin requirement and glycemic control of dogs with stabilized diabetes.14 The two trial diets had high-fiber and moderate-starch content, but varied in fat. The control diet was a commercial dog food with moderate-fiber, low-starch, and higher fat content. Diabetic control evaluated every 2weeks included history, physical examination, and 2-hourly blood glucose measurements over 12h. Insulin dose was adjusted based on standardized criteria to maintain control of glycemia. At the end of each 2-month feeding period, glycemic control was evaluated by plasma fructosamine, glycosylated hemoglobin, and 48h serial blood glucose measurements. No significant differences in insulin requirement or glycemic response among diets were found. It was concluded that, for stable diabetic dogs, high-fiber, moderate-starch diets offer no significant advantage for insulin requirement or glycemic control compared to a commercial diet with moderate-fiber and low-starch content.

DIETARY CARBOHYDRATE AND CANINE DIABETES

Evidence based on randomized trials in non-diabetic dogs

Little is known about the glycemic responses of diabetic dogs to various carbohydrate-containing foods. The amount of starch in the diet has been shown to be the major determinant of the glycemic response of healthy dogs across a wide range of typical commercial dog foods.15 A study examining the postprandial effects of five diets with equivalent starch content (30%) from different cereal sources found marked differences in the glucose and insulin responses of healthy dogs.16,17 The rice-based diet resulted in significantly higher postprandial glucose and insulin responses. Sorghum generally caused the lowest postprandial glucose response while barley produced the lowest insulin response. These findings form an interesting basis for future study on the effects of diets containing sorghum in diabetic dogs and the effects of diets containing barley in bitches with diestrus-induced insulin resistance, but more work is required before specific recommendations can be made. It is worth noting that studies in humans have found a marked variability in the glycemic response to different types of barley18 and rice. 19

DIETARY FAT AND CANINE DIABETES

Evidence based on expert opinion, clinical experience, and pathophysiological rationale

Altered lipid metabolism occurs with insulin deficiency in dogs, yet there are minimal published data on the influence of dietary fat on diabetic dogs. In humans, the lipid disorders that occur in association with diabetes are arthrogenic and predispose to coronary artery disease.20 Restricted-fat diets reduce cardiovascular morbidity and mortality in diabetic people. Although artherosclerosis and coronary artery disease are not usually a concern in diabetic dogs, artherosclerosis has been reported in association with spontaneous canine diabetes.21 Perhaps of greater clinical relevance is that diabetes secondary to exocrine pancreatic disease appears to be common in dogs, and the diabetic state may also be a risk factor for pancreatitis. High-fat diets and hypertriglyceridemia have been proposed as possible inciting causes of canine pancreatitis22,23, and low-fat diets are recommended for dogs with chronic pancreatitis and exocrine pancreatic insufficiency. As it can be difficult to identify those diabetic dogs with subclinical exocrine pancreatic disease24, it may be prudent to consider feeding a fat-restricted diet to all diabetic dogs. This may have the added benefit of improving insulin sensitivity in animals with insulin resistance-associated diabetes and reducing the risk of overt diabetes in bitches during diestrus.

Evidence based on a randomized, controlled clinical trial in diabetic dogs

The same randomized, controlled trial that assessed the influence of canned, high-fiber, moderate-starch diets on insulin requirement and glycemic control of dogs with stabilized diabetes also assessed the influence of dietary fat.14 Different amounts of dietary fat in the high-fiber, moderate starch diets had no significant influence on insulin requirement or glycemic control of the dogs. Lower dietary fat content was associated with significantly improved lipid profiles. The low fat, high fiber, moderate starch diet resulted in significantly lower mean total cholesterol concentration compared with either of the other diets, and significantly lower mean LDL-cholesterol, total glycerol, and free fatty acids than the commercial diet. It is unknown whether any health benefits for dogs may be attributed to these improvements in the lipid profile. Significant weight loss occurred when the dogs were fed the low-fat, high-fiber, moderate-starch diet, whereas maintenance of weight was achieved with both of the other diets. It was concluded that diets with lower fat content may result in improved lipid profiles in diabetic dogs, but may contribute to weight loss.

DIETARY PROTEIN AND CANINE DIABETES

Evidence based on pathophysiological rationale

The protein composition of the recommended diet for people with diabetes is the same as that recommended for the non-diabetic population.25 However, if microalbuminuria or persistent proteinuria develop, then protein restriction may help slow the progression of diabetic nephropathy in these people.26 The optimal dietary protein for diabetic dogs has not been determined. Microalbuminuria and proteinuria do occur in diabetic dogs27 and lower dietary protein intake may be indicated in these animals.

DIETARY CARNITINE AND CANINE DIABETES

Evidence based on pathophysiological rationale

Carnitine is a conditionally essential, vitamin-like nutrient that plays a pivotal role in fatty acid metabolism. Supplemental carnitine suppresses acidosis and ketogenesis during starvation in dogs.28 Carnitine supplementation at 50ppm of diets fed to dogs enhances energy derivation from fatty acid oxidation and protects muscles from catabolism during weight loss.29-31 In cats, dietary supplementation of carnitine also provides a protective effect on liver function during fasting.32 Dogs with poorly controlled diabetes experience weight loss, altered fat metabolism, ketogenesis, and hepatic changes, and so are likely to benefit from dietary carnitine supplementation. The majority of diabetic dogs are middle-aged and older and can be expected to already have reduced lean body mass33 before the onset of diabetes-associated weight loss. Consequently, it is important to consider any dietary intervention, such as carnitine supplementation, that promotes maintenance of lean body mass in these animals.

DIETARY CHROMIUM AND CANINE DIABETES

Evidence based on pathophysiological rationale and a controlled clinical trial in diabetic dogs

Chromium tripicolinate is a dietary mineral supplement that has been shown to increase the clearance rate of glucose from the blood by approximately 10% in healthy dogs.34 Chromium is an essential nutrient, not a drug, and therefore supplementation may only result in benefits if the individual is deficient or marginally deficient in chromium. It is now clear that dietary chromium levels of most people in industrialized countries are sub-optimal.35 Similar information is not available for dogs and further studies are warranted to try and establish the minimum recommended dietary chromium intake for healthy dogs. Chromium is thought to potentiate insulin's ability to store glucose and would theoretically be useful in dogs with insulin resistance or as an adjunct to exogenous insulin therapy. It is also possible that inadequate dietary intake of chromium by dogs may increase their risk of developing diabetes. It has been postulated that some insulin-dependent diabetic people may lose their ability to convert inorganic chromium to the biologically active form and may actually need to consume foods that contain active forms of chromium.36 At this stage, there is little information available on the effects of chromium supplementation in human patients requiring insulin therapy.37,38 Supplementation with chromium picolinate capsules has been found to not improve glycemic control in insulin-treated dogs.39 The influence of chromium supplementation on bitches with diestrus-induced insulin resistance is unknown.

SUMMARY OF DIETARY RECOMMENDATIONS FOR CANINE DIABETICS

The American Diabetes Association uses a grading system to rank the scientific principles of their nutritional recommendations. The highest ranking, A, is assigned when there is supportive evidence from multiple, well-conducted studies; B is an intermediate rating; C is a lower ranking assigned to evidence such as that not reported in peer-reviewed publications; and E represents recommendations based on expert consensus. If this grading system is used to rank the scientific basis of the nutritional recommendations for canine diabetes, current evidence can be summarized:

The diet fed to diabetic dogs should be palatable so that food intake is predictable (Grade E).

The diet fed to diabetic dogs should be nutritionally balanced (Grade E).

The nutritional requirements of any concurrent disease should take precedence over the dietary therapy for diabetes (Grade E).

As a regimen of fixed daily insulin dosages is typically used to manage diabetic dogs, it is rational to provide a consistent amount of carbohydrate in the meals fed each day (Grade E).

Controlled evaluation in non-diabetic dogs of diets with different amounts and types of fiber indicate that increased fiber intake has no significant influence on glucose homeostasis, compared to typical diets formulated for canine adult maintenance (Grade B).

Although several studies in diabetic dogs indicate that high-fiber diets, compared to low-fiber diets, may be associated with improved glycemic control (Grade B), randomized, controlled comparison identified no measurable benefit for insulin requirement or glycemic control in diabetic dogs, compared to a conventional, moderate-fiber diet formulated for adult maintenance (Grade C).

High-fiber diets do not significantly improve hypertriglyceridemia in diabetic dogs but may lower serum cholesterol concentrations (Grade B).

There seems to be marked variation between the responses of individual diabetic dogs to dietary fiber (Grade B).

When moderate-fiber diets are fed to diabetic dogs, a blend of soluble and insoluble fibers (such as soy fiber) might be preferable to insoluble fiber alone (Grade C).

Comparison in non-diabetic dogs found that a rice-based diet resulted in significantly higher postprandial glucose and insulin responses, while a sorghum-based diet caused reduced glucose responses, and barley produced lower insulin responses (Grade C).

Diets with lower fat content may result in improved lipid profiles in diabetic dogs, but may also contribute to weight loss (Grade C).

The optimal dietary protein for diabetic dogs has not been determined. Lower dietary protein might be indicated in diabetic dogs with microalbuminuria or proteinuria (Grade E).

Diabetic dogs may benefit from dietary carnitine supplementation (Grade C).

Supplementation with chromium capsules has been found to not improve glycemic control in insulin-treated dogs (Grade B).

References