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Obesity and Weight Management in Cats

Adopted from: Fat Cats: Understanding Feline Nutrition, Western Veterinary Conference 2010, Debra L. Zoran, DVM, PhD, DACVIM-SAIM

Obesity is a growing problem in cats worldwide. Depending on the study cited, the number of obese or overweight cats ranges from 15% to 35%, with practitioners estimating even higher numbers in some areas. Obesity is defined as an excess of body fat, with a body weight of greater than 20% over the ideal weight of the cat being generally accepted as obese.

Key Points:

  1. Obesity prevention must start early, and your team of veterinarians and technicians are essential to recognition, early intervention, and success

  2. Neutered cats are far more prone to obesity than intact cats

  3. Prevention of obesity in neutered cats requires careful control of calorie intake beginning immediately after neutering

  4. Most average sized, indoor, neutered cats weighing 4-5 kg (9-11 lb) need to eat less than 200 kcal/day and many (especially males) may need even less than 180 kcal/day to maintain lean body condition

  5. High protein, low carbohydrates, low fat diets are ideal for weight loss in cats because they preserve muscle mass while restricting energy sources that will induce fat loss

Obesity is just not a cosmetic problem as it increases:

  1. the risk of development of diabetes

  2. the risk of hepatic lipidosis

  3. the incidences of many other conditions such as lower urinary tract disease and osteoarthritis in cats

  4. it also will shorten their life span

The cause of obesity in any animal is that they are consuming more energy than they are expending. Unfortunately, it is not that simple. There are many other factors that may control or play significant roles in appetite, metabolism, and the development of obesity. It is important to for us to develop a concerted effort to recognize risk factors, monitor young and middle-aged cats carefully, to catch weigh gain early, promote the importance of obesity prevention and the health benefits of weight control. To this end we have provided the information below. Obesity prevention must start early, and your veterinary team is essential to recognition, early intervention, and success.

There is now ample evidence in both male and female cats, that neutering is an important risk factor for obesity in the feline. For some time, we have recognized that many cats had significant weight gain after neutering or during their adolescent years, but most believed this was due entirely to the type or amount of food fed, and not due to other factors. Several recent studies have shown that multiple hormonal changes occur immediately following removal of the sex organs that have a significant effect on feline metabolism.

The key factor for prevention of obesity in neutered animals appears to be careful control of calorie intake immediately after neutering (no free choice feeding, reduction of intake by 25% to account for the hormonal changes resulting in reduced energy needs), and close monitoring of body weight and Body Condition Score (BCS) to allow adjustments in intake if needed.The key factors that result in increase in body weight are castration and free choice access to food.

In simple terms, most average sized, indoor, neutered cats weighing 4-5 kg (9-11 lb) need to eat less than 200 kcal/day and many (especially males) may need even less than 180 kcal/day to maintain lean body condition. This is a significantly smaller amount of food than often recommended and represents a critical change in feeding recommendations for cats–one that will be extremely difficult to achieve if the cat is being fed a calorie dense (high fat) food or is allowed free access to dry food.

Problems of “free choice” method of feeding

Because the preferred feeding method of many cat owners and veterinarians is feeding “free choice” (available all of the time) dry food, this practice must be addressed. There are several reasons that this method of feeding is not an appropriate method of feeding for many cats, and particularly indoor, neutered, and inactive cats.

The first, and potentially most important problem with this feeding approach is the risk of overfeeding (or overeating), which even in very small amounts can exceed appropriate caloric intake and result in weight gain.

The second, and potentially equally important issue with “free choice” feeding is that there is no way for owners to assess a cat’s intake on a daily basis. One of the most important ways for owner to assess the health status of their cats–especially in households with multiple cats–is to monitor their appetite and intake.

Finally, because free choice eating requires cats to consume dry food as their sole food source, it creates two other potential problems that may not be immediately obvious: reduced water intake and preference for dry food only. While this situation does not create a problem for all cats, and it may not seem like an important issue at first glance, there are insidious concerns that may occur with this approach.

What diet should I feed?

Cats, unlike most domestic species, are true carnivores, and thus must either consume animal flesh and fat to meet their nutritional needs or their diets must be supplemented appropriately with the necessary amino acids and fatty acids that they are unable to synthesize from other food sources like omnivores. Nevertheless, the most commonly used food for cats is a dry, extruded (vegatable based) diet. While these commercially available cat foods are nutritionally complete and balanced, are readily available, easy to use and store, and are quite palatable, they bear little resemblance to a diet of a natural carnivore. It can be argued that cats have done quite well on this feeding approach–as their lifespan has increased from single to double digits, as they die less of injury, infectious disease, or predation, but from diseases of aging: cancer, kidney disease, and other chronic conditions. While it is clear that easy access to affordable, balanced nutrition for cats is a great benefit to both cats and their owners alike, it is also becoming increasingly obvious that diet and lifestyle factors have resulted in major new health risks for our cats.

Examples of diseases or disorders that may be associated with the type of diet are:

  1. the rising percentage of obesity

  2. the increase in diabetes mellitus

  3. the number of cats with chronic (diet induced) diarrhea or inflammatory bowel disease (IBD)

We have an obesity crisis, and we need to rethink how we feed our cats, and consider that just because “that’s how we have always done it”, it is not too late to re-evaluate our approach to feeding cats.


Repeatedly, investigators have shown that the amount of total protein in the diet is a key aspect of success in weight loss. When restricting calories for weight loss, it may be wise to even increase the protein content of the diet fed to a very high level.diets Otherwise, cats will experience muscle wasting. This is an important point because loss of muscle mass during weight loss is detrimental to general well being, is a major determinant of metabolism, and in cats in particular, may be one the keys to eventual success. Obese cats on high protein diets not only have improved insulin sensitivity, they have greater energy metabolism and fat burning–resulting in great loss of fat mass during calorie restriction and weight loss.

Conclusion: High protein diets are vital in obese cats. High protein is essential for preservation of lean body mass during calorie restriction and weight loss, and is important for increasing insulin sensitivity–a key means of preventing further development of glucose intolerance (pre-diabetes)


Carbohydrates are a major part of most dry and some canned commercial diets due to issues of processing, preservation, and cost. Carbohydrates serve two major purposes: they are an energy source (simple carbohydrates and starches such as cereal grains are examples) or they are complex carbohydrates typically described as dietary fiber and present for their actions in bowel as fibers. Carbohydrates in high quality commercial foods are generally highly digestible and provide a readily available energy source. The problem is that most indoor cats are relatively sedentary, the carbohydrate that is not used for energy will be stored as fat. Cats can digest, absorb and use carbohydrates quite well. In a recent study investigators showed that cats allowed outdoor access (or at least had enhanced activity) and fed only carbohydrates at levels necessary to maintain a Body Condition Scor of 5/9 can be fed dry diets (higher in fiber and carbohydrates) quite effectively without an increased risk of diabetes or obesity.

The key point is that carbohydrates fed to cats that are active and receiving appropriate portions of food will likely not lead to obesity or diabetes; however, this aspect is crucial to their ability to consume carbohydrates in their diet. Unfortunately, the circumstances of many cats today are that they are neutered, indoor and sedentary. Consuming large amounts of their diets (e.g., 35-50%) as carbohydrates in a free choice will result is that they will gain weight.


The role of fat in diets is extremely important in feline obesity, as fat provides the greatest amount of energy per gram of diet. As a result, there are a number of low fat diets commercially available for calorie control in cats. Further, several recent studies show that controlling calories from fat in weight loss programs is an essential part of achieving successful weight loss. That being said, dietary fat has many roles in metabolism beyond being a powerful source of energy, as there are key differences in feline requirements for fat must be considered when choosing a diet. In cats, being a carnivore also means that they require additional supplementation of fatty acids (especially arachidonic acid) and fat-soluble vitamins in their diet that normally would come from the fat stores of prey. Further, cats will often reject diets with too little fat or diets where the fat is oxidized, as fat is a major palatability enhancer. So, while reducing fat in feline diets is an important method of controlling calories in feline diets, there are no studies in cats showing the ideal amount of fat in the diet. And, as with protein and carbohydrate in the diet, it is essential to consider that whole diets for weight loss in cats should ideally be higher in protein, lower in fat (to control calories), but containing essential fatty acids in enough quality to meet their requirements, and lower in carbohydrates (to prevent reduction in energy metabolism, and conversion of excess carbohydrates to fat).


The final dietary component to consider in weight loss diets is dietary fiber. In general, most weight loss diets add insoluble or mixed sources of fiber to the ration, such as cellulose or beet pulp or other fiber mixtures. Dietary fibers have been used in weight loss diets for many years due to their ability to dilute calories and provide fill to the diet so that larger volumes of food could be fed during energy restriction. Fiber aids in both glycemic and weight control by promoting slow, sustained glucose (and other nutrients) absorption from the gastrointestinal tract, and by increasing the speed of passage of food through the small intestine. However, this effect, while beneficial for weight loss, results in reduced digestibility of protein and may result in other untoward effects. Many owner and cats do not tolerate diets with moderate to high levels of dietary fiber (>15% dry matter) as it can cause increased fecal volume, constipation, food refusal and dry skin. There are no studies available that demonstrate an optimum amount or type of dietary fiber for use in cat foods for any purpose; however, a moderate (5-12% dry matter) amount of mixed fiber may be best. If fiber is added to the diet, the effects on protein digestibility must be considered, and an appropriate amount of additional protein added to the food to prevent a reduction in protein availability. High fiber in the diet should not be considered a “cure all” for weight loss, but it can be included as part of the overall approach to controlling caloric intake in cats if the diet contains increased amounts of dietary protein.

Calculating Calories

Successful weight loss in an obese cat is possible, but requires patience, setting goals, frequent monitoring, re-adjustment, and appropriate understanding. The key is to set a target calorie intake, then weigh the cat monthly, and adjust the amount of food based on weight loss. While the most appropriate rate of weight loss is debated, most agree that a goal of 1% weight loss per week or 3-4% per month is a safe target. If, during periods of monitoring, this goal is not being achieved, a reduction in calories (by 5-20%) must be done to meet the weight loss goals.

The number of dry diets that meet this profile is extremely small, primarily because most high protein, low carbohydrates dry foods are formulated either as diabetic diets or kitten foods, and may contain too many calories.

For example, a typical dry diabetic or kitten food contains 500-600 kcal/cup of food. These diets are extremely calorie dense due to their high fat content, and as a result, it is extremely difficult to feed an appropriate amount to a cat that requires weight loss. For example, in an obese cat, the target intake may need to be as low as 130-150 kcal/day, so the amount of the high calorie diabetic dry food fed at a meal will be quite small.

The best commercial diets for achieving a high protein, low carbohydrates, low to moderate fat profiles are canned cat foods.

For example, a typical diabetic, or high protein/low carbohydrates canned diet will have from 165-190 kcal per 5.5 oz can. When the target for caloric intake is 180kcal or less, it can be easier to achieve the high protein necessary to preserve muscle mass in a portion controlled diet with this approach. While there are many canned foods that have a high protein/low carbohydrates profile, it is also important to recognize that it is not universal–canned foods can be high carbohydrate, low protein, or have poor quality ingredients resulting in ineffective or unhealthy weight loss. The key is to remember that “one size does not fit all” in cat foods–and careful reading of the label can help determine the protein, carbohydrate and fat levels, which is the start of the process.


The key point for obesity prevention (or correction) is balancing the energy intake / energy expenditure equation. Because obesity is incredibly difficult to reverse in the adult cat, prevention is an essential goal. All neutered cats are at risk for development of obesity due to the changes in their hormonal balance that affect appetite, energy balance, and fat metabolism. Because of these changes, food intake must be carefully restricted following castration or spaying in all cats, and free-choice feeding of dry foods is to be strongly discouraged. In indoor cats, where exercise is reduced by the nature of the lifestyle, energy restriction also becomes paramount to obesity prevention or correction. Energy restriction can be achieved by low fat – high fiber diets, but many of these diets are not high enough in protein to preserve muscle and thus, result in loss of muscle mass and result in an unhealthy weight loss and a strong tendency to regain weight (muscle mass loss will always increase the likelihood of regain). High protein, low carbohydrates, 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 of >45% ME, and a low level of carbohydrates (< 10% ME) and fat. The key to any successful weight loss program is:

  1. patience and persistence

  2. frequent and careful monitoring and assessment

  3. and readjustment of the caloric intake and diet as needed to achieve fat loss and preserve lean muscle tissue.


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