Feline diabetes mellitus: From diagnosis to therapy (Proceedings)
Overview of diabetes mellitus in cats
Like the disease in humans, diabetes in cats is a multi-factorial process combining genetic factors with environmental ones. However, there are two factors that likely have a crucial role in determining whether or not diabetes develops, and if diabetes does occur, whether or not it is insulin dependent. The first of these determining factors in the majority of cats is the presence of persistent hyperglycemia (either as a result of the phenomenon of glucose toxicity or due to one of many factors causing insulin resistance), which is general believed to be the first step in the development of diabetes in the majority of cats. Second major factor that influences the course of the disease is the duration and severity of disease that ultimately results in beta cell damage or destruction. Once islet destruction has commenced, the disease becomes less likely to have a reversible outcome and the need for chronic insulin therapy to achieve control of blood glucose is assured. Thus, the classification of diabetic cats into Type I (insulin dependent or IDDM), Type II (non-insulin dependent or NIDDM) or transient diabetics can be very difficult, frequently confusing, and often in error, because some cats appear to not require insulin initially, and then progress to insulin dependency later. Other cats flip back and forth between insulin dependency and not, as the severity of the impairment of beta cell function, insulin resistance, and other factors wax and wane. These apparent flip-flops are understandable when one realizes the huge variation that occurs in these three things that are important in determining the diabetic state in cats: 1) islet pathology may be quite variable (mild to severe, static to progressive), 2) the ability of the pancreas to secrete insulin is dependent on the degree of islet pathology (which can change with time), and 3) the peripheral tissue responsiveness to insulin, which varies due to many factors (e.g. obesity, inflammatory, infectious, neoplastic or hormonal disorders). Each of these different variables can affect the need for insulin, the dose of insulin, and the overall ease of patient management.
PathophysiologyWhile figures vary, recent studies indicate that greater than 35-40% of cats in the United States are overweight or obese. There are a large number of factors that contribute to this problem, including sex (intact vs. neutered, male vs. female), age, activity (indoor vs. outdoor), and feeding style (meal feeding vs. free choice). However, the fact remains that obesity is a significant contributor to morbidity in middle aged to older cats. Further, as we are all aware, "it is much harder to take it off, than it is to put it on". One factor that is increasingly being considered, both in the development of and treatment of obesity, is the role of carbohydrates (CHO) as excess calories in diet. Because of the preference for cats to utilize protein as an energy source, CHO in the diet that are not immediately used for energy (e.g. via exercise or other utilization for energy) will be stored as fat. Recent studies have also shown that cats consuming diets containing moderate levels of CHO had lower resting energy rates than cats on high protein, low CHO diets – thus creating the situation that even requires an even lower intake to prevent over-nutrition. Furthermore, diets higher in CHO can be a major contributing factor to development of glucose toxicity which can lead to the development of islet malfunction and ultimately, pre-clinical diabetes mellitus. These factors will be further discussed in the sections below.
Recent studies indicate that 25-40% of cats in the United States are overweight or obese. There are a large number of factors that contribute to this problem, including sex (intact vs. neutered, male vs. female), age, activity (indoor vs. outdoor), and feeding style (meal feeding vs free choice). In a recent paper studying the effects of neutering on hormones and obesity, two very important findings were uncovered: 1) after neutering a rapid increase in IGF-1 and prolactin occurs that is closely followed by an increase in body weight, and 2) dysregulation of glucose metabolism (in association with increases in leptin levels that are significant enough to cause insulin resistance). Thus, to prevent the deleterious effects of these hormonal changes, prevention of obesity by reducing food intake and careful monitoring of body weight becomes essential. Further, because "it is much harder to take it off, than it is to put it on" – it is important to control weight and diet from the onset (in kittens). Another factor that is increasingly being considered, both in the development of and treatment of obesity, is the role of CHO in the feline diet. Because of their metabolic requirement to utilize protein as an energy source, CHO in the diet that are not immediately used for energy (e.g. via exercise or other utilization for energy in addition to the protein they utilize for energy) will be stored as fat. Successful weight loss requires loss of adipose tissue as well as maintenance of lean body mass, as lean body mass is the driver of basal energy metabolism (loss of lean body mass is a major contributor to weight regain as appetite is not reduced and satiety not reached). Several recent studies have evaluated use of a high protein, low CHO diet (protein 45% or higher) for weight loss in cats, and in those studies, all cats lost weight, but maintained lean body mass. Importantly, high protein, low carbohydrate diets not only result in sustained weight loss in these cats, but also in normalization of appetite (reduced urge to eat constantly because they are satiated). Because dry foods must be extruded to form the kibble, CHO are required in the cooking process, and thus, the best commercial diets for achieving a high protein, low CHO profile are canned (e.g. may be adult or kitten) foods. However, it must be stated that high protein, low CHO diets are not "magical" – their profile is ideal for cats, but the number of calories consumed is the critical key to appropriate weight reduction and control. High protein/low CHO dry foods are generally very calorically dense (m/d has 485 kcal/cup, DM has 580 kcal/cup, Ennova ENO has 540 kcal/cup, etc), and can be difficult to feed in appropriate amounts to achieve target calories. On the other hand, canned foods have lower calories/unit (m/d canned has 165 kcal/can, DM has 180 kcal/can, etc). An important consideration is that most cats need to eat no more than their resting energy requirement to stay at their ideal body weight. However, in cats for which weight loss is needed, a reduction of 60-80% of RER will likely be necessary to achieve weight loss. What does this mean? The veterinarian must counsel cat owners both on the type of food and the amount of food they feed their cats to not only prevent obesity, but to treat it when it is present.