Does diet matter when treating feline diabetes mellitus?Domestic cats (Felis catus) are amazing creatures that evolved from wild ancestors known to be obligate carnivores or hypercarnivores. November 1, 2019 By Aline Bomfim Vieira, DVM, MSc, PhDA recent study found an increased risk of diabetes with dry food consumption in lean cats. Domestic cats (Felis catus) are amazing creatures that evolved from wild ancestors known to be obligate carnivores or hypercarnivores. Obligate carnivores possess several physiologic adaptations to consume a diet based on prey, which have minimal amounts of carbohydrates. The term obligate carnivore is constantly used to describe animals that consume a diet composed of at least 70 percent animal tissue.1 What type of physiologic adaptations to a low-carbohydrate diet do cats demonstrate? First, while many humans (omnivores) experience cravings for sugar, cats demonstrate indifference toward it. Studies have shown they lack the expression of at least one gene (tas1R2) necessary to detect the taste of sweet.2,3,4 In addition, cats do not possess salivary amylase, an enzyme to initiate in the mouth the digestion of some types of carbohydrates.5 Another interesting difference between cats and omnivores is minimal to absent activity of glucokinase (GK) enzyme in the liver.6,7 This enzyme is important to catalyze the first reaction of glucose metabolism in cells, which is the phosphorylation of glucose to glucose-6-phosphate. In other words, GK is the first and the rate-limiting step in glucose utilization leading to glucose storage as glycogen. The conversion of glucose into glycogen is one of the key pathways by which the liver removes glucose from the portal vein after a meal. We still do not know exactly how glucose phosphorylation can efficiently occur in cats in the absence of GK. On the other hand, we do know cats have limited ability to rapidly minimize hyperglycemia from a large dietary glucose load. Considering all physiologic peculiarities of obligate carnivores, a lot of discussion has emerged over the past decade about which type of diet would better suit the domestic cat. With domestication and urbanization, cats have been exposed to a sedentary life full of carbohydrate-rich diets. This “new” lifestyle might be linked to the development of feline obesity and diabetes mellitus. The role of diet in the development of diabetes Diabetes mellitus is one of the most common endocrine disorders of domestic cats, but probably rare in free-living felids. In the U.S., a study showed an increase in feline diabetes mellitus prevalence over 30 years from one in 1,250 (0.08 percent) in 1970 to one in 81 (1.2 percent) in 1999.8 Although studies on environmental risk factors for diabetes in cats are scarce, the growth of prevalence is most likely associated to the increase in predisposing factors, such as obesity and physical inactivity. Obesity is a growing global health problem that includes domestic cats. When evaluating more than 8,000 adult cats in the U.S., a study found 35 percent of them were either overweight or obese.9 Being overweight is one of the most important risk factors for feline diabetes, and obese cats are known to have four times more risk of developing diabetes than lean cats.10 Although non-modifiable factors like genetics and age can play a role in the development of obesity, the excessive accumulation of adipose tissue is caused usually by an imbalance between energy intake and expenditure. It is logical to think diet, as a source of excessive calories, would play a central role in the development of obesity and consequently diabetes in cats. Here are some important points about diet and the risk of obesity and diabetes mellitus in cats: High-protein/low-carbohydrate versus high-carbohydrate diets The potential role of high-protein/low-carbohydrate diets in preventing diabetes mellitus in cats has not been shown yet. However, studies have found cats on high-carbohydrate diets may be prone to weight gain and fat accumulation.11 Therefore, a high-carbohydrate diet could directly induce obesity and indirectly increase the risk of diabetes in cats. In healthy cats, diets rich in carbohydrates lead to higher postprandial glucose and insulin concentrations, which are believed to be involved in beta cell failure and the pathogenesis of feline diabetes.12 We also know obese cats on high-protein/low-carbohydrate diets achieve weight loss more effectively, compared to cats on moderate-protein diets. High-protein diets preserve lean muscle mass and show a trend to maintain a stable weight after weight reduction.13 A high-protein and low-carbohydrate diet is defined as a diet containing ≥ 40 percent protein metabolized energy (ME) or protein content greater than 10g/100kcal and carbohydrate < 12 percent to 15 percent ME. This is easily obtained using canned/wet diets.14 Wet versus dry food Only two epidemiological studies so far have found wet versus dry food to be a determinant risk for diabetes in cats.15,16 The first found a consumption of a mix of wet and dry foods was associated with a lower risk for diabetes,15 while the most recent one showed an increased diabetes risk with dry food consumption in lean cats.16 To better elucidate the role of diet as a risk factor for diabetes, well designed studies are required. On the other hand, when treating obesity, a study showed wet/canned food provided more satiety (less begging behavior) to cats compared to dry, high-fiber diets. This is probably linked with the additional water intake and increased volume provided by wet foods.17 Table 1 lists some wet diets commonly used to treat obesity and diabetes mellitus in cats and their approximate nutrient content. Food amount Overfeeding is an important factor to induce obesity in cats, and consequently, could be linked to the development of diabetes mellitus. Free choice or ad libitum feeding of inactive, indoor cats must be avoided.14 A good dietary plan must include calculation of daily caloric requirements based on lean body mass. The next section presents dietary recommendations for diabetic cats. Energy intake versus expenditure is an important pillar of obesity. All epidemiological studies available so far agree that living indoors, physical inactivity, and increasing age are very important risks factors for feline diabetes.14 Physical activity in cats can be encouraged using environmental enrichment (e.g. vertical spaces that allow them to jump). In addition, the bouncing light of a laser pointer, as well as placing water and food in separate areas, could stimulate walking and increase activity levels. Dietary management Preventing feline diabetes and managing it do not necessarily require the same approach. Although we still have unanswered questions about the role of diet in the development of feline diabetes, we do have strong guidelines to treat the disease.18 Diabetes mellitus in cats usually resembles the disease in humans, and most patients have type 2-like diabetes mellitus. They present impaired insulin action in liver, muscle and adipose tissue (insulin resistance) combined with beta cell failure. The first step when treating feline diabetes is to initiate insulin therapy. For more about insulin therapy in cats, refer to American Animal Hospital Association’s (AHAA’s) 2018 Diabetes Management Guidelines for Dogs and Cats. Management of feline diabetes mellitus requires an individualized treatment plan, frequent reassessment, and modifications based on the cat’s response. The dietary therapy for diabetic cats should pay attention to the type and amount of diet to optimize the patient’s weight. In other words, it is important to induce weight loss in obese cats or stop diabetes-associated weight loss through the feeding of a high-protein diet.18 High-protein diets in the form of wet/canned foods are preferred over dry food when feeding a diabetic cat, since they provide lower carbohydrate content, good palatability, additional water intake, higher volume, and easier portion control (Table 1). Studies have shown a better glycemic control and higher remission rates when low-carbohydrate diets were combined with insulin therapy.19,20,21 Free choice feeding is acceptable for problematic cats. Preferentially, the total amount of food is divided into two meals that will be provided by the time of insulin injection. Any leftover food should remain available for the rest of the day/night. The following approach is recommended to initiate diet management in diabetic cats: Determine the patient’s body weight and use the same scale for future reevaluations Determine its body condition score (BCS) and recheck monthly to adjust diet therapy Calculate the amount of food based on resting energy requirement (RER) using the cat’s estimated ideal weight – RER (kcal/day) = (Ideal body weight kg x 30) +70 – For more information on how to estimate ideal body weight, see 2014 AAHA Weight Management Guidelines for Dogs and Cats Feed half the portion at the time of each insulin injection For overweight/obese cats, the weight loss goal is 0.5 to 2.0 percent reduction per week Feline diabetes mellitus is a complex and challenging disease requiring a committed effort by veterinarians and clients. Diabetic cats can now benefit from new insulin formulations and continuing glucose monitoring. The American Association of Feline Practitioners (AAFP) recently released the Diabetes Educational Toolkit to provide veterinarians with the most relevant diagnostic and treatment information for this disease. The toolkit is available online at bit.ly/2ESUjiT and can be downloaded and printed. Aline Bomfim Vieira, DVM, MSc, PhD, is assistant professor of veterinary physiology at Ross University School of Veterinary Medicine. She has a passion for teaching and has been a lecturer in the field of physiology, endocrinology, and metabolism since 2007. Dr. Vieira also is an active researcher and her interests include endocrine physiology and endocrine/metabolic diseases with a focus on obesity and diabetes mellitus. References 1 Holliday JA, Steppan SJ. Evolution of hypercarnivory: the effect of specialization on morphological and taxonomic diversity. Paleobiology (2004)30:108–28. 2 Bartoshuk LM, Jacobs HL, Nichols TL, Hoff LA, Ryckman JJ. 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