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25 NOVEMBER/DECEMBER 2017 ■ TVPJOURNAL.COM NUTRITION NOTES Many pets with diabetes have increased thirst or may experience polydipsia/polyuria, so fresh, clean water should be available at all times. Energy (calorie density) depends on body condition and whether the pet needs to gain or lose weight to obtain ideal body condition. Although not yet directly linked to outcomes in diabetes, protein and fat should be considered in pets with some comorbid conditions. For example, dogs with concurrent pancreatitis or hyperlipidemia may need dietary fat restriction, while overweight cats and dogs may need increased protein to ensure that their essential needs are met while they undergo calorie restriction. Chromium, a trace mineral, has been evaluated as a potential nutrient of concern because of its involvement in glucose regulation, but studies have not shown clinical benefit to supplementation. 1 Optimal levels of fiber and carbohydrates differ between species and are discussed in detail below. UNDERSTANDING FIBER Different types of fiber can have different properties and benefits (or adverse effects). Fiber types can be defined in a few ways. In a clinical setting, however, describing fibers by their solubility in water is the most relevant. Soluble fibers, such as pectins and gums, are best at absorbing water. Adding soluble fiber can promote healthy colonic mucosa and immune function in the colon, but this type of fiber is not as active in glucose control. Insoluble fibers, such as cellulose, have less water-holding capacity, but by adding bulk, they can slow absorption of dietary carbohydrate, which can be a benefit to glucose regulation in diabetic dogs. Some ingredients, such as beet pulp, are mixed-fiber sources and may have some of the benefits of both soluble and insoluble fibers. Although the term "high-fiber diet" can be confusing, a rough estimate of the amount of insoluble fiber in a food is the crude fiber content. Of note, percentages on pet food labels are "guaranteed analyses" and thus indicate only a maximum or minimum; they cannot be compared between diets of different moisture or calorie content. a CANINE DIABETES Although terminology varies, this article uses the clinically applicable terms insulin-dependent diabetes mellitus (IDDM) and non–insulin-dependent diabetes mellitus (NIDDM). Dogs are more commonly diagnosed with IDDM; thus, while diet can play an integral role in management, it should be used in conjunction with medical management. The first aspect of dietary management to consider should be calorie density. Dogs with diabetes can present underweight, overweight, or even at ideal weight, so focusing on achieving or maintaining ideal body weight can guide diet choice based on calorie density. Calorie density is also intricately associated with another important nutrient of concern for diabetic dogs, fiber, which is commonly used to dilute calorie density. Diet selection based on individual pet needs can therefore be critical. For example, a food high in fiber and low in calorie density would be contraindicated for an underweight dog that cannot eat enough of the food to meet its energy needs. The Case for Fiber Although it would seem logical to reduce dietary carbohydrates in both dogs and cats for better glucose control, research has shown that for dogs, carbohydrate content in diets is not as clinically beneficial as fiber content. In fact, a study showed no difference in diabetic control in dogs fed canned diets that differed in carbohydrates by a factor of 9 (ie, 2% carbohydrate metabolizable energy [ME] vs 26% ME). 2 Research shows that the effect of insoluble fiber on diabetic control in dogs is more promising. Researchers found that dogs with naturally occurring IDDM had better fasting blood glucose and urinary glucose excretion while on a high-fiber diet (6.0 g/100 kcal) compared with a lower-fiber diet (2.6 g/100 kcal). 3 Another clinical trial comparing diets with differing soluble and insoluble fiber concentrations showed that dogs with naturally occurring IDDM had better glycemic control while on the diet with high insoluble fiber. 4 A challenging confounder in these studies is the correlating caloric dilution that results from the addition of fiber. It is not known whether the mechanism of action providing benefit is the addition of insoluble fiber itself, the subsequent lower calorie density, or the combination of the two. For dogs in which higher fiber is not contraindicated, the evidence suggests that diets with higher insoluble fiber may help with diabetic control after dogs are stabilized with medical management. a For more information on fiber and comparing fiber contents of diets, see "Featuring Fiber: Understanding Types of Fiber and Clinical Uses" in the 2017 January/February issue of Today's Veterinary Practice on tvpjournal.com .