Q & A: Best Diet for Dogs with Diabetes Mellitus

I have a 10-year old, male, 4-kg Miniature Pinscher that has been on twice daily NPH insulin injections (0.75 U/kg per injection) for the last 6 months. Because of his diabetes, we have been feeding Hill's Prescription w/d diet. Overall, the serum glucose curves are quite good, the polyuria and polydipsia have resolved, and the dog seems to feels great. However, despite being well controlled, the dog has been losing weight and has lost over 1.5 kg since diagnosis.

The main problem is that the dog continues to be ravenous and is loosing weight. Despite being well controlled on his blood glucose curved, the dog has lost over 1.5 kg since diagnosis.

Am I feeding the wrong diet? I thought that all diabetic dogs did best when fed a high fiber diet such as Hill's w/d.

My Response:

First of all, there is not one type of diet that is recommended for all dogs with diabetes. Diabetic dogs can do well when fed a number of diets as long as they are nutritionally complete and balanced, do not contain simple sugars, are fed at consistent times in consistent amounts, and are palatable to ensure a predictable and consistent appetite. As we all know, it's difficult enough to regulate a diabetic when they are eating consistently well— if they refuse to eat their diet, adequate glucose regulation can become next to impossible.

In many newly diagnosed diabetic dogs, I don't change their diet at all.  The most important dietary factor in the diabetic is consistency, so that you can match your insulin dose to the degree of post-prandial hyperglycemia. The owner must understand that the key is to feed the same amount of the same diet at the same time every day!

In general, the goals of dietary therapy in canine diabetes mellitus are four-fold:

1. Optimize the dog's body weight and body condition score (i.e., weight loss versus weight gain, as needed)
2. Minimize post-prandial hyperglycemia
3. Control hyperlipemia and hypertriglyceridemia
4. Modify the diet based any concurrent conditions (e.g., pancreatitis, kidney disease, gastrointestinal disease)

Optimize Body Weight
In diabetic dogs that are obese, I always recommend feeding a reduced calorie diet designed to help the dog lose weight. The high fiber diets are good for this purpose (1-4). No matter what diet is fed, however, it's also important to limit the amount of fat in the diet when weight loss is the goal. To me, an appropriate weight loss diet should contain restricted amounts of fat — less than 30% on a metabolizable energy (ME) basis, which means <30% of the calories in the diet supplied by fat.
(For more information about how to calculate ME values for fat, protein, and carbohydrates, see Calculating the Metabolizable Energy (ME) Values of a Dog Food, below.)

In underweight dogs with diabetes, the goal of dietary therapy is the complete opposite. In these thin dogs. our priority is to normalize body weight and restore and preserve muscle mass. These dogs may never regain the weight needed if a food with moderate to high amounts of fiber is fed — they may even continue to progressively lose even more weight. Therefore, these thin to emaciated dogs should be fed a high-quality, higher energy diet that can contain a slightly increased fat content to ensure that they regain their lost body weight (3,4).

Minimize Post-prandial Hyperglycemia
Several "older" landmark studies showed that feeding high-fiber diets can improve glycemic control in dogs with diabetes (1,2). The extra dietary fiber slows the digestion and absorption of carbohydrates, and thereby helps to minimize post-prandial hyperglycemia (1-4).

However, there are disadvantages in feeding all diabetic dogs a high-fiber diet. Again, because these diets tend to promote weight loss, they are not suitable for the thin or emaciated dog with diabetes (5). In addition, the high dietary fiber content of the food can result in unwanted side effects, including inappetence, diarrhea, and flatulence in some dogs.

Other more recent studies fail to show a clear-cut clinical benefit of feeding a high-fiber diet over a typical adult maintenance diet with moderate-fiber content to diabetic dogs.  In one study, no significant differences in insulin requirements or glycemic control were found in dogs fed a high-fiber, moderate-carbohydrate, moderate-fat diet versus an adult maintenance diet with moderate fiber, lower carbohydrate, and higher fat (5). As expected, weight loss occurred when the dogs were fed the high-fiber diet, whereas body weights were maintained with the moderate-fiber diet.

For any dog food, the major potential influence on the postprandial glycemic response is the dietary carbohydrate source (6-8). Foods and snacks containing simple sugars which rapidly increased blood glucose should always be avoided, of course. Feeding carbohydrate sources that have a low glycemic index (e.g, sorghum and corn) are preferred for diabetic dogs. Carbohydrates with a higher glycemic index (e.g., rice) are best avoided (6).

Because dogs are omnivores, they can tolerate higher amounts of carbohydrates better than do diabetic cats. Therefore, I recommend a diet that is moderately restricted in carbohydrate content — that is, a diet with <30% metabolizable energy (ME) as carbohydrates— for diabetic dogs to limit their post-prandial glucose load and help control hyperglycemia.

Control Hyperlipemia and Hypertriglyceridemia
A diet containing restricted amounts of fat (again, <30% ME) should be fed to diabetic dogs with concurrent hypertriglyceridemia or hyperlipidemia (4,9).

The presence of hyperlipidemia (i.e., hypertriglyceridemia and, to a lesser degree hypercholesterolemia) has long been associated with pancreatitis in dogs (9). Hyperlipidemia is common in untreated or poorly controlled diabetes mellitus and may contribute to the concurrent pancreatitis that can develop in these diabetic dogs. For my diabetic patients with concurrent pancreatitis, I've had good luck with the Royal Canin Veterinary Diet Gastrointestinal Low-Fat LS diet — it contains the lowest amount fat of any of the commercial diets (15% ME for fat), and most dogs find it quite palatable.

However, some dogs with diabetes secondary to chronic pancreatitis also have partial loss of exocrine pancreatic function and can be at risk for excessive weight loss when fed a low fat diet. One approach for the underweight diabetic dog with hypertriglyceridemia is to consider restricting dietary fat intake only after adequate glycemic control has been established. In these dogs, both body weight and serum triglyceride concentrations are followed carefully, and dietary adjustments are made as needed.

High Protein Diets in Canine Diabetes?
The optimal dietary protein for diabetic dogs has not been determined. But it does not appear that the protein requirement for a diabetic dog would be much different than a non-diabetic dog. However, because we frequently aim for either carbohydrate or fat restriction (or both), dietary protein will often provide a substantial source of calories for diabetic dogs (for example, protein >30% ME).

Calculating the Metabolizable Energy (ME) Values of a Dog Food
The most accurate way to evaluate pet foods and their composition is to consider the calories or metabolizable energy (ME) that comes from the protein, fat, and carbohydrate fractions (10). This allows us to compare various diets without worrying about their different fiber, ash, or moisture content.

Remember that the percent carbohydrates, fat, and protein of any diet can be expressed in at least 3 ways — as fed, on a dry matter basis, or on a metabolizable energy (ME) basis. Depending on how the diet composition is expressed, the same food may list a percent carbohydrate value that appears to be very low to rather high (for example, 5% or 25%). As an analogy, if you buy hamburger at the grocery store and the label says it's 90% lean and 10% fat, you might determine that it is composed mostly of protein and is low in fat. But if you calculate the composition of the hamburger on a caloric or energy basis (ME), the hamburger is actually half fat and only half protein. That's why the ME basis is the best to really determine what we are actually feeding.

However, unless you are able to obtain the ME values for a diet from the company (always the best way), you may need to estimate the values from the guaranteed analysis (GA) listed for the diet. I like to use the Guaranteed Analysis Converter found on the Balance IT Professional web site to help make this calculation easier (11). The actually calculations are not that difficult but are somewhat cumbersome to perform (10).

The Bottom Line
Dogs should never be fed a high-fiber diet just because they have diabetes. Many dogs do just as well on other maintenance diets containing lower amounts of fiber and carbohydrate and higher amounts of protein. A consistent diet —that is, the type, amount, and time of feeding —is generally much more important in diabetic regulation than any particular fiber content or specific type of diet.

References:

1. Nelson R, Duesberg C, Ford S, et al. Effect of dietary insoluble fiber on control of glycemia in dogs with naturally acquired diabetes mellitus. Journal of the American Veterinary Medical Association 1998;212:380–386. 
2. Graham PA, Maskell E, Rawlings L. Influence of a high fibre diet on glycaemic control and quality of life in dogs with diabetes mellitus. Journal of Small Animal Practice 2002;43:67–73. 
3. Rucinsky R, Cook A, Haley S, et al. American Animal Hospital Association.AAHA diabetes management guidelines. Journal of the American Animal Hospital Association 2010; 46:215-224. 
4. Zicker SC, Nelson RW, Kirk CA, et al. Endocrine Disorders. In: Hand MS, Thatcher CD, Remillard RL, Roudebush R, Novotny, BJ (eds), Small Animal Clinical Nutrition. Mark Morris Institute. 2010; 559-584.
5. Fleeman LM, Rand JS, Markwell PJ. Lack of advantage of high-fibre, moderate-carbohydrate diets in dogs with stabilised diabetes. Journal of Small Animal Practice 2009;50:604-614. 
6. Rand JS, Farrow HA, Fleeman LM, et al. Diet in the prevention of diabetes and obesity in companion animals. Asia Pacific Journal of Clinical Nutrition 2003;12 Suppl:S6.
7. Elliott KF, Rand JS, Fleeman LM, et al. A diet lower in digestible carbohydrate results in lower postprandial glucose concentrations compared with a traditional canine diabetes diet and an adult maintenance diet in healthy dogs. Research in Veterinary Science 2011;96; 288-95. 
8. Nguyen P, Dumon H, Biourge V, Pouteau E. Glycemic and insulinemic responses after ingestion of commercial foods in healthy dogs: influence of food composition. Journal of Nutrition (12 Suppl):2654S-2658S. 
9. Xenoulis PG, Steiner JM. Lipid metabolism and hyperlipidemia in dogs. The Veterinary Journal 2010;183:12-21. 
10. Laflamme DP. Determining metabolizable energy content in commercial pet foods. Journal of Animal Physiolology and Animal Nutrition (Berlin). 2001; 85:222-230. 
11. Balance IT Professional Website. Guaranteed Analysis Converter.