Diabetes mellitus (DM) is the second most common endocrinopathy in cats, estimated to affect 0.5 percent of cats (O’Neill et al., 2016). In comparison to dogs, where type 1 DM accounts for the majority of diabetic cases, type 2 DM is the most common form in cats, affecting 80 to 95 percent of feline diabetics (Rand et al., 2004), with beta cell loss or dysfunction caused by insulin resistance, islet amyloidosis or chronic pancreatitis. Remission is possible and is often a key aim of nutritional management, unlike in dogs, where remission is very rare. In addition to insulin injections, nutritional support can have an important role in the management of diabetic cats, and this article will give an overview of key factors to consider.
Optimising body weight
Optimising body weight is a crucial goal of nutritional management in cats. Where DM-associated pathological weight loss is present, this should be halted. Obesity significantly reduces insulin sensitivity; overweight cats are up to four times more likely to develop DM (Prahl et al., 2007) and obesity will contribute to ongoing insulin resistance. Increased incidence of obesity is thought to be one of the main factors contributing to the increased incidence of diabetes being recorded (Prahl et al., 2007). Appropriate weight loss can help glycaemic control and aid the likelihood of remission in cats (Sparkes et al., 2015) and may be a key aim in many diabetic cats. Body weight and body condition should be monitored regularly (eg every one to two weeks) in all diabetic cats. In many cases, this can be done at home; for example, owners can be educated to use a body condition scoring chart appropriately, and some cats may be amenable to being weighed in a bowl on kitchen scales. A weight loss goal of 0.5 to 1 percent per week is reasonable.
Choosing the right diet
Managing protein and carbohydrate intake is important to minimise post-prandial hyperglycaemia.
Diabetic cats should be fed a high-protein diet (defined as at least 40 percent protein on a metabolisable energy (ME) basis; Behrend et al., 2018). This can maximise metabolic rate, limit the risk of hepatic lipidosis during weight loss, improve satiety and prevent lean muscle mass loss. Protein helps to normalise fat metabolism and helps provide a consistent energy source. Protein also delays the time to peak glucose levels in the blood, which can reduce the likelihood of glucosuria and associated clinical signs (Frank et al., 2001).
Carbohydrate intake should be restricted because carbohydrates may contribute to hyperglycaemia and glucose toxicity (Behrend et al.,
2018). By limiting dietary carbohydrate, blood glucose is maintained primarily by hepatic gluconeogenesis, which releases glucose into the circulation at a slow steady rate, avoiding post-prandial fluctuations in blood glucose concentrations. The optimal dietary carbohydrate level has not been determined, although diets of 12 percent ME carbohydrates or less have been recommended (Sparkes et al., 2015; Behrend et al., 2018). Further studies, however, are required to determine the optimal level of restriction.
Cat foods with a higher carbohydrate level (including most dry foods, except therapeutic dry cat foods specifically designed for the management of DM) are not recommended as a first choice (Sparkes et al., 2015). Diabetic cats have reported remission rates of 15 to 100 percent when given a combination of a high-protein/low-carbohydrate diet and insulin, and obtaining good glycaemic control within the first six months after diagnosis is a key predictor of likelihood of remission (Behrend et al., 2018). If remission is achieved, cats should remain on the diabetic diet long term.
A number of studies have demonstrated the role of high-protein/low-carbohydrate diets in the control of feline DM, and some of the main ways a high-protein/low-carbohydrate diet can help are detailed in Box 1. Frank et al. (2001) fed adult cats with DM of at least four months’ duration a commercial high-fibre/moderate-fat canned diet for one to two months during the standardisation period. All cats were then transitioned to a commercial high-protein/low-carbohydrate diet for three months. During the study period, exogenous insulin requirements decreased in 89 percent of cats, insulin injections were stopped (remission achieved) in 33 percent of cats and exogenous insulin could be reduced by over 50 percent with no loss in glucose control, as measured by serum fructosamine. The test diet used is available as a therapeutic diabetic diet within the UK.
High-fibre diets are not typically recommended for cats with DM, in contrast to dogs. Frank et al. (2001) demonstrated these to be inferior to the use of high-protein/low-carbohydrate diets in diabetic control. In another study of 63 diabetic cats receiving insulin and maintaining a stable body weight during the study, cats were significantly more likely to revert to a non-insulin-dependent state when fed a canned low-carbohydrate/low-fibre food compared to a medium-carbohydrate/ high-fibre food (Bennett et al.,
Consideration of the format of the diet is important. Where possible, wet foods (pouches or cans) are preferred over dry foods since they have reduced carbohydrate levels. They also contain a lower caloric density which is desirable during management of obesity: cats can eat a higher volume of canned food and obtain the same caloric intake as smaller volumes of dry food (Sparkes et al., 2015). For owners, wet foods can make portion control easier and may help compliance during weight management programmes. Feeding a 100 percent wet diet can also support hydration status (Greco et al., 2014), which is particularly desirable when clinical signs of DM such as polyuria remain.
Timing and frequency of feeding is less important in cats compared to dogs, although at this stage optimum feeding regimes are poorly investigated (Sparkes et al., 2015). Timing of meals does not need to be matched to insulin injections given the lack of post-prandial hyperglycaemia in cats, although for many owners injecting insulin at a meal time may be easier (Sparkes et al., 2015). The frequency of feeding is also not critical, and where cats have previously been “grazers”, continuing with this routine is recommended in many cases. Minimising the number of changes to a routine that an owner has to make may also help with owner compliance. Accurate portion control is important, particularly during management of obesity and in order to enable owners to accurately monitor food intake and appetite. In such cases, use of timed feeders may help (Behrend et al., 2018).
With respect to diet transition, any transition made in a diabetic cat (or dog) should be relatively slow, given that it may impact on glycaemic control. However, because of the potential for remission in diabetic cats, this diet transition should be done over a prolonged period of time (eg 28 days). Where possible, owners should test the urine of a diabetic cat for glucose daily; if it becomes negative, this suggests a potential reduction in exogenous insulin requirements and should prompt assessment by the veterinarian (Sparkes et al., 2015). Monitoring water intake at home can also be a good indicator of response to insulin and of remission for owners. If remission does occur, cats should remain on a low carbohydrate diet long term, rather than revert to a diet designed for a healthy cat. As in dogs, providing a written dietary plan for the owner, including the type and amount of food to be fed daily and an area for notes with respect to the amount eaten, clinical signs (for example, water intake), insulin dose and body weight (particularly where weight loss is a goal) can be helpful.
The key nutritional factors, timing and frequency of feeding differ between cats and dogs with DM, as has been discussed in these two articles. However, dietary modification plays an important role in the management of DM to help maximise glycaemic control in both species, and in cats also to potentially achieve remission. In cats, the nutritional profile of the food has a particularly significant role, whereas the timing of feeding and consistency of routine is of lesser importance in the cat compared to the dog. Dietary support can also have a key role in supporting any coexisting conditions that may complicate diabetic control and should always be considered in the management plan of any diabetic patient.