Obesity is a growing problem in cats worldwide, but, in Western societies, the incidence of excess weight and obesity in cats is reaching truly worrisome numbers.
Obesity is a growing problem in cats worldwide, but, in Western societies, the incidence of excess weight and obesity in cats is reaching truly worrisome numbers. Studies have indicated that 15% to 35% of cats in the United States are overweight or obese, and practitioners estimate even higher percentages in some areas.1 Obesity is defined as having a body weight 20% or more above the ideal weight. In other words, a 4-kg (9-lb) cat that gains 1 kg (2 lb) is considered obese. Using this definition, it would not be surprising for feline obesity to approach 70% in some practices. Furthermore, obesity is not just a cosmetic problem. In cats, it increases the risk of diabetes and hepatic lipidosis and is associated with increased incidences of many other conditions, such as lower urinary tract disease and osteoarthritis.2 This serious medical condition not only increases morbidity, but can also shorten life span. Considering the number of affected cats and the challenge of getting a seriously obese, 12-kg (26-lb) cat to weigh 4.5 kg (10 lb), it is obvious that the situation demands our full attention.
To successfully address feline obesity, practitioners must recognize obesity as more than just overeating but as an endocrinopathy, and they must be able to develop safe and effective weight loss programs and help every member of the veterinary team understand how important it is to prevent young cats from gaining excess weight in the first place.
The most obvious reason for any animal becoming obese is that it is consuming more energy than it is expending. In cats, this energy imbalance can occur when there is an excessive intake of calories (food or treats) or a reduction in energy expenditure (reduced activity because of an indoor lifestyle, illness, or injury). However, there are many other factors that play significant roles in the development of obesity. These factors include genetic predisposition, sex, neuter status, hormonal disturbances, and other conditions that can influence or control appetite, metabolism, and homeostasis. As a result, it is important to:
In other words: act before the cat is obese! Obesity prevention must start early, and the veterinary team is essential to recognition, early intervention, and successful lifestyle changes.
For both male and female cats, neutering is an important risk factor for obesity.3,4 Many cats gain significant weight after neutering or during adolescence, and it had been believed that this gain was due entirely to the type or amount of food fed and not due to other factors. However, several recent studies have shown that multiple hormonal changes occur immediately after removal of the sex organs, and these changes have a significant effect on appetite, metabolism, and other hormones determining metabolic status.3,5-7
The metabolic changes include alterations in levels of leptin, progestins, estrogen, prolactin, insulin-like growth factor (IGF-1), and other hormones.3,5-7 The results are an increase in appetite, a reduction in energy metabolism, changes in glucose tolerance and lipid metabolism, and in the case of IGF-1, an increase in the number and size of adipocytes.
Spayed and neutered cats undergo a startling series of hormonal changes that affect food intake (they have an increased appetite) and energy metabolism (their energy needs are decreased) that results in an increase in body fat mass that may be inevitable unless appropriate measures are taken to monitor and limit intake — particularly in indoor or sedentary cats. To prevent obesity in these cats, careful control of intake (no free-choice feeding) immediately after neutering (a reduction in intake of at least 25% to 30% is essential) and close monitoring of body weight and body condition score (BCS) are necessary to make the appropriate adjustment. Several studies have evaluated the role of different amounts of dietary components (e.g. fat or carbohydrates) in relation to obesity, but the key factors that result in increased body weight are gonadectomy and freechoice feeding.5,8-10
Another consideration is that feeding cats according to traditional maintenance energy calculations will result in significant overfeeding and development of obesity. Those equations were based on intact cats, and the amounts recommended are 25% to 35% higher than most housecats need. Nutritionists continue to debate what is an appropriate number of calories for maintenance energy intake in cats, and numbers range from 20 to 100 kcal ME/kg/day. Multiple papers have suggested that 70(BWkg)0.75 represents resting energy requirements, and 94 to 125(BWkg)0.75 are accepted ranges for maintenance energy intake for cats.11 However, recommendations from the National Research Council (NRC) recommend 130(BWkg)0.40 for obese cats and 100(BWkg)0.67 for lean cats.12 Feeding studies of neutered cats have shown that feeding cats typical maintenance amounts of food results in weight gain and, more importantly, fat mass gain.5,10 In an analysis of the caloric needs of colony cats, it was reported that neutered female cats required 100(BWkg)0.40 and neutered males required 120(BWkg)0.40 to maintain ideal body condition.13 In other recent studies, investigators determined that neutered cats consuming more than 50 to 60(BWkg)0.67 gained weight, and their BCS increased from ideal to obese in just three months.14
From these data it can be concluded that most average-sized, indoor, neutered cats weighing 4 to 5 kg (9 to 11 lb) need to eat less than 200 kcal/day to maintain lean body condition. And, neutered males, in particular, may need to eat even less (approximately 180 kcal/day). This represents a critical change in feeding recommendations for cats and will be difficult to achieve if the cat is being fed a calorie-dense (high-fat, energydense) dry food or is allowed free access to ANY dry food.
For indoor cats, inactivity and reduced energy expenditure are important problems for weight management. It is difficult to increase energy expenditure in cats through induced exercise; however, the sedentary lifestyle of many indoor cats is detrimental to their physiologic and psychological health and wellbeing. Exercise is vital to health because it maintains and strengthens lean muscle tissues, promotes cardiovascular health, provides mental stimulation, reduces stress, improves quality of life, increases energy expenditure and fat oxidation, and increases the metabolic rate.
If feasible, cats should be given access to a protected outdoor area, which is a great stimulus for play or exercise. Cats that are unable to be outdoors should be given other opportunities to fulfill their physiologic needs for climbing, balancing, scratching, and exercise. This requirement can be met in many ways and can be tailored to the cat's needs and the situation. For example, cat toys may work well for some, cat trees or play stations are excellent for others, and interactive toys that reward the cat with food can also stimulate activity. Owners don't need to turn mice loose in their house to encourage play, but they do have to engage cats to create play opportunities. Play and activity are essential to a healthy feline life and necessary for indoor cats to have an improved lifestyle, increased muscle mass, and a reduced risk of obesity.
Another risk factor for obesity in cats is the preferred feeding method of many cat owners: freechoice dry food. There are several reasons that this feeding method is not appropriate for many cats, particularly indoor, neutered, inactive cats. First is the risk of overeating, which, even in small amounts, can cause the cat to exceed its appropriate caloric intake and gain weight. The second problem is that control of intake is essential for neutered cats because they have an altered hormonal balance that results in increased appetite and decreased energy expenditure rate. A further problem with this feeding method is that it is impossible for owners to determine a cat's daily food intake, and one of the best ways for owners to assess the health status of their cats — especially in multicat households — is to monitor their appetite and intake. Subtle signs of illness may be easily missed with free-choice feeding.
Finally, because free-choice feeding requires cats to consume dry food, it creates two other potential problems — reduced water intake and a preference for dry food only. Cats normally consume a large portion of their water in their diet and often do not adequately compensate for the absence of water in dry food. Cats fed dry foods have to drink at least 2 ml of water per gram of dry food consumed.15,16
Research on feline drinking behavior shows us that even though cats fed dry foods do drink more, they generally do not take in the same amount of water as cats that eat canned food. Cats that eat canned food consume significantly greater amounts of water per gram of dry matter in the food. Further, dietary studies show that water intake is significantly increased in cats consuming diets high in protein (> 45% ME) and less in cats consuming typical dry foods.16,17 Inadequate water intake can increase the risk for dehydration, constipation, urolithiasis, and other lower urinary tract conditions. However, adding canned foods to the diets of adult cats is not that easy.
Cats develop strong food preferences early in life. These food preferences influence what cats will eat later in life, and these behaviors are learned, highly conserved, and intense. If a cat does not eat canned foods early in life (at weaning and the first months after weaning) and then does not continue to eat them, it often refuses to consume them later. Cats that develop conditions requiring canned foods for disease management (e.g. lower urinary tract disease, constipation, diabetes, kidney disease) often will not consume them if they have been fed only dry foods previously. This is because their food preferences were ingrained when they were kittens and became habituated when they were adults.
Veterinarians need to understand this feline behavior and instruct owners to expose cats to multiple types and flavors of food early and throughout their lives. That will make it possible to change a cat's diet later should it become necessary. In summary, freechoice dry food feeding is not an appropriate feeding method for optimal nutrition for indoor, neutered cats — even if they are of optimal body condition.
A number of factors contribute to the development of feline obesity, but diet is an important component in any prevention or treatment plan. Cats, unlike most domestic species, are true carnivores. They must consume animal flesh and fat to meet their nutritional needs, or their diets must be supplemented with the amino acids and fatty acids that they are unable to synthesize from other food sources. Nevertheless, the most commonly used foods for cats are dry, extruded diets. Though these commercial cat foods meet NRC minimums, are nutritionally complete and balanced, and are readily available, easy to use and store, and palatable, they bear little resemblance to the diet of a natural carnivore. These considerations should be taken into account whenever a weight loss or maintenance diet plan is being prescribed.
Cats, as obligate carnivores, use protein as an energy source, even when other energy sources such as fat or carbohydrates are available.
In the past, most veterinary researchers have focused on fat and carbohydrate energy sources and their roles in preventing and managing obesity. Although it is essential to reduce caloric intake to achieve weight loss in cats, in the process, many have overlooked protein's role in feline metabolism and overall health. Hoenig and coworkers showed that cats fed high-protein diets (> 45% ME) had increased energy metabolism, higher fat oxidation, and improved glucose tolerance, while cats consuming high-carbohydrate diets had lower energy metabolism, required fewer calories to meet needs, and gained fat mass.18 Other researchers have shown that, as obese cats lose weight, higher protein levels result in greater loss of fat mass and better preservation of muscle mass.19-21 Repeatedly studies have shown that the amount of protein is key in weight loss diets, since even cats consuming protein at 45% ME lost some muscle mass during diet restriction. This suggests that even higher amounts of protein may be needed during weight loss because of the severe intake restriction needed to reduce calories and lose weight. Particularly in cats, preserving muscle mass is essential to controlling obesity, as muscle mass is a major determinant of basal metabolism and insulin resistance.
Thus, even though lean cats appear to adapt to lower-protein, higher-carbohydrate diets, cats on high-protein diets have improved insulin sensitivity and have greater energy and fat metabolism. This results in greater loss of fat mass during calorie restriction and weight loss. Increased protein intake may be particularly important in cats following weight loss, as research shows that energy expenditure remains decreased.22,23 Therefore, a high-protein diet (> 45% protein ME) is essential for treating obese cats to preserve lean body mass during calorie restriction and weight loss and for increasing insulin sensitivity, helping to prevent further development of glucose intolerance.
Protein is only one part of the feline diet. Carbohydrates are a major component of most dry and some canned commercial diets because of processing, preservation, and cost issues. Carbohydrates serve two major purposes: they are an energy source (e.g. simple carbohydrates and starches, such as cereal grains) and they are dietary fiber (complex carbohydrates) fed for their actions in the bowel. In the discussion of feline obesity, those digestible carbohydrates serving as an energy source should be addressed. While the digestibility and glycemic index of dietary carbohydrates can vary by source, carbohydrates in high-quality commercial foods are generally highly digestible and provide a readily available energy source. In fact, the role of carbohydrates in any diet, whether for dogs or cats, is as an energy source. If the cat is active and needs energy, the carbohydrate will be used efficiently. However, if the cat is sedentary, the carbohydrate that is not used for energy will be stored as fat. The amount and type of carbohydrates in the feline diet are important for several reasons:
1. Cats' ability to handle dietary carbohydrate loads is very different than that of omnivores.
2. Since cats use protein for energy, even in times of excess energy in the diet, sedentary or inactive indoor cats often do not utilize the carbohydrate energy in the diet.
3. High-carbohydrate diets reduce the resting energy metabolism, so cats must consume less food to maintain appropriate body weight.
The difference in feline metabolism does not mean that cats are unable to use carbohydrates — quite the contrary — cats can digest, absorb, and use carbohydrates quite well. The type of carbohydrate is important, though, as there are significant differences in glycemia, postprandial glucose levels, insulin secretion, and food intake between normalweight and obese cats. However, a recent study also showed that cats allowed outdoor access (or that had increased activity) and only fed amounts necessary to maintain a BCS of 5/9 can be fed dry diets quite effectively without an increased risk of diabetes.24 The key point is that carbohydrates fed to cats that are active and receiving appropriate portions of food probably will not lead to obesity or diabetes; however, the amount of protein in the diet and their activity level are crucial. Unfortunately, the circumstances of many cats today are that they are neutered, sedentary, and consume large amounts of their diets (35% to 50%) as carbohydrates in a free-choice or poorly controlled feeding regimen. The result is weight gain.
The role of dietary fat is another consideration in feline obesity, since fat provides the most energy per gram of food. Consequently, there are a number of low-fat commercial diets available for calorie control in cats. Several recent studies have shown that controlling calories from fat in weight loss programs is essential to achieving weight loss.5,10 Dietary fat plays many roles in metabolism, beyond being a powerful source of energy, and there are key differences in feline requirements for fat that must be considered when choosing a diet. For example, cats require supplementation of some fatty acids and fat-soluble vitamins that would naturally come from prey.
Furthermore, cats will often reject diets with too little fat or diets in which the fat is oxidized, as fat is a major palatability enhancer. Yet, while reducing fat in feline diets is an important method of controlling calories, there are no studies showing the ideal amount of fat in a feline diet. Ideally, feline diets for weight loss should be higher in protein (> 45%, to attain the metabolic and muscle-preserving aspects of protein), lower in fat (to control calories) but with enough high-quality essential fatty acids to meet cats' requirements, and lower in carbohydrates (to avoid reduced energy metabolism and prevent conversion of excess carbohydrates to body fat).
The final component to consider in feline weight loss diets is fiber. Most weight loss diets contain insoluble or mixed sources of fiber, such as cellulose or beet pulp. Dietary fibers have been used in weight loss diets for many years because they dilute calories and provide fill so that larger volumes can be fed during energy restriction. Fiber aids in both glycemic and weight control by promoting slow, sustained absorption of glucose (and other nutrients) from the gastrointestinal tract and by increasing the speed at which food passes through the small intestine. Whereas this effect is beneficial for weight loss, it reduces the digestibility of the dietary protein and may result in other untoward effects. However, a recent study comparing diets differing only in whether they had high-moisture or high-fiber content on their effects on food intake and body weight in cats showed that high-moisture foods resulted in maintenance of weight with much less begging and more effective control of calorie intake than high-fiber foods did.25
Further, many owners and cats do not tolerate diets with moderate to high levels of dietary fiber (> 15% dry matter) because they can cause increased fecal volume, constipation, food refusal, and dry skin.
No studies have been done to determine an optimal amount or type of dietary fiber for use in cat foods; however, a moderate amount of mixed fiber (5% to 12% dry matter) may be better than very high fiber amounts. If fiber is added to the diet, the effects on protein digestibility must be considered, and protein may need to be added to prevent a reduction in protein availability or protein deficiency. High fiber in the diet should not be considered a "cure-all" for weight loss in cats, but increased fiber can be part of the overall approach to controlling caloric intake if the diet also contains increased amounts of dietary protein.
Weight loss in an obese cat is absolutely possible but requires patience, goal setting, frequent monitoring, and readjustment of feeding strategies. You and your clients need to understand that reversing obesity is a difficult challenge similar to the management of any other chronic endocrinopathy — persistence and diligence are essential. The key is to set a target calorie intake, then weigh the cat weekly, and adjust the amount of food monthly based on the weight loss. The most appropriate rate of weight loss is debated, but it is generally accepted that 1% weight loss per week or 3% to 4% per month is a safe target. If, during monitoring, this weight loss goal is not being achieved, calorie intake must be reduced further (by 5% to 20%). Any adjustment in diet should be accompanied by careful monitoring of overall health and weight loss.
Healthy weight loss requires loss of adipose tissue along with maintenance of lean body mass, since lean body mass is an important controller of basal energy metabolism. So, ideally, weight loss diets should have protein levels higher than 45% ME and should be low in calories (i.e., low in fat and carbohydrates). The number of dry food choices with this profile is extremely small. Most high-protein, low-carbohydrate dry foods are formulated as either diabetic diets or kitten foods and, thus, are high in calories (and many are also high in fat and energy dense). For example, a typical dry diabetic or kitten food contains 500 to 600 kcal/cup of food. In an obese cat, the target intake may be as low as 130 to 150 kcal/day, so the amount of the high-calorie diabetic dry food fed at a meal will be quite small (< ⅛ cup twice daily). This amount is probably too small to achieve any sense of fullness and will likely result in annoying begging behavior that reduces owner compliance. The best commercial diets for achieving a high-protein, low-carbohydrate, moderately low-fat profile are canned cat foods. A typical diabetic (high-protein and low-carbohydrate) canned food contains from 165 to 190 kcal/5.5-oz can. Thus, when the target for caloric intake is no more than 140 to 150 kcal, it is easier to achieve the high protein necessary to preserve muscle mass in a portion-controlled diet with this food. While there are many canned foods that have a high-protein, low-carbohydrate profile, it is not universal. Canned foods can be high in carbohydrates, low in protein, or have poor-quality ingredients, resulting in ineffective or unhealthy weight loss. Remember that "one size does not fit all" in cat foods. Read the labels carefully to help determine the protein, carbohydrate, and fat levels.
The goals of a weight-reduction program are much easier to achieve if a cat starts a weight loss program when it only needs to lose 4 to 5 lb. A morbidly obese cat that weighs more than 9 kg (20 lb) (and thus is 50% body fat) will require a much more concerted and sustained effort to achieve even modest success. Remember, to lose fat mass and preserve muscle, a weight loss program must consider the cat's body condition at the start, the degree of energy restriction required, the rate of weight loss that you plan to achieve, and the cat's environment and the ability to increase its exercise.
Although the strategy is relatively straightforward, it requires patience, careful and long-term monitoring, encouragement and support for the owner, and frequent assessment and readjustment to meet the individual cat's needs.
There are a number of weight loss programs available to help veterinarians and clients manage their obese patients, such as the Nestlé Purina Veterinary Feeding Guide and Weight Management Program. The Purina program is a computerized feeding program that customizes patient feeding recommendations and produces professional feeding plans for most Nestlé Purina diets. You can create patient feeding plans for effective, individualized weight loss and management.
For obesity prevention or correction, the key is balancing the energy intake-energy expenditure equation. Obesity is incredibly difficult to reverse in the excessively obese adult cat and, in many cases, requires lifelong management. Therefore, obesity prevention is essential. All neutered cats are at risk of developing obesity because of changes in their hormonal balance that affect appetite, energy balance, and fat metabolism.
Because of these changes, food intake must be carefully restricted following gonadectomy in all cats, and free-choice feeding of dry foods is strongly discouraged. For indoor cats, where exercise is reduced, energy restriction is also needed for obesity prevention or correction. High-protein, lowcarbohydrate, low-fat diets are ideal for weight loss in cats because they preserve muscle mass while restricting energy sources that will induce fat loss. However, portion control is ultimately the key to controlling energy intake — and the easiest way to achieve portion control is to feed canned food with a protein content greater than 45% ME and a low level of carbohydrates (< 10% ME). Canned foods are also better at providing satiety in cats than highfiber foods are, so switching to a canned diet is an important strategy.
By Debra L. Zoran, DVM, PhD, DACVIM
Department of Small Animal Clinical Sciences
College of Veterinary Medicine and Biomedical Sciences
Texas A&M University
College Station, Texas
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