Introduction
In the United States today it is estimated that at least 25% of cat cats are overweight. One older study done in the United Kingdom (Anderson, 1973) reported a prevalence of obesity in this species at 6 to 12%. In the last few decades, however, we have seen a steady increase in the popularity of cats as pets and an increase in the percentage of those cats that are confined indoors. In addition, more cats are neutered and there is increasing evidence that neutering has an impact on food intake (increasing it) and energy expenditure (decreasing it). The results of an epidemiological study of 2,053 cats living in the eastern U.S. in 1991–92, found that 20% of the cats examined were judged to be overweight (by a veterinarian) and an additional 5% were judged to be obese.
There are numerous documented adverse effects of obesity on the health of humans. Less information is available for our feline patients. In the study done by Scarlett and Donoghue, multivariate statistical analysis controlled for age showed obesity to be a risk factor for diabetes mellitus, skin problems, and lameness. The investigators also found that the middle-aged obese cats had a 2.7-times greater risk of mortality than cats at optimal body weight.
One consequence of obesity in cats is abnormal insulin secretion. There is a well-known association between obesity and non-insulin-dependent diabetes in people. Both obese dogs and cats have been shown to have glucose intolerance and hyperinsulinemia. The relevance of these findings to the pathogenesis of diabetes mellitus in cats is currently unknown but is under investigation at a number of veterinary institutions. In addition to diabetes mellitus, retrospective studies of feline lower urinary tract disease and feline idiopathic hepatic lipidosis have found obesity to be a risk factor for these diseases.
While the adverse effects of obesity on the health of pet cats may not be easily quantified, there is no good reason why these cats should be allowed to become overweight and run any risk at all. While their owners may struggle with a host of social, psychological, and physiological obstacles to maintaining an ideal body weight, it should be relatively easy to prevent their cats from becoming overweight. Cat owners need to be educated about the effects of neutering, how to objectively evaluate their pet’s body condition, and how to adjust feeding practices accordingly. Less than one teaspoon of a typical dry cat food a day more than a cat needs to meet its energy needs can add up to a pound of body fat in one year!
Designing a Weight Reduction Program
Animals become overweight when their energy intake exceeds their energy expenditure (i.e., the animal is in a positive energy balance). The excess energy is stored primarily as triglycerides in adipose tissue. Weight loss is achieved by putting the animal in negative energy balance. This can be done by increasing their energy expenditure, decreasing their energy intake, or doing both.
Increasing a cat's energy expenditure generally requires a greater commitment on the part of the owner and may meet with failure even when pursued with great dedication. Therefore, in most cases, the weight loss program will be centered on dietary intervention. The key in restricting energy intake is to have a notion of what the cat’s current energy intake is. This can be difficult to ascertain depending on whether the cat is given food other than commercial cat food, how many animals are in the household, and how many people are feeding the cat. In multi-cat households obtaining this type of information is often a challenge.
Obviously, the first thing to do before advising a client on a weight loss program is to do a complete physical exam and get a thorough dietary history. While probably only a very small percentage of overweight cats have an underlying endocrine problem like hypothyroidism, it is necessary to diagnose those cases and manage them appropriately in order to have any success with the weight loss program. The dietary history should consist of an accurate accounting of all foods fed to the cat on a typical day. This must include brand names of commercial cat foods and treats and specific amounts fed. Record the amounts of table food fed and if the diet is home cooked get a complete recipe. Find out if the cat has access to the food fed other cats in the household, whether there are other family members feeding the cat (especially small children), and whether the cat can roam to beg, hunt, or scavenge food. Don’t forget to inquire as to whether the cat is receiving any regular medications that are disguised with food. It may be impossible to quantitate the cat's energy intake from this information, but it will alert you and the cat owner to possible problems you may face in implementing the weight loss program. The owner may have to go home and keep a food diary for a few days before they can actually answer these questions.
There are several different ways of calculating the amount of caloric restriction a cat will have to undergo to lose weight. The first step for any of them is to decide upon your weight loss goal. This should not necessarily be based upon the cat's ideal body weight. Rather, it should depend more on just how overweight the cat is. It is more important to set a reasonable goal and accomplish it than to set an ambitious goal and have the client get discouraged and give up. It may be necessary to repeat a program several times for an individual animal in order to reduce it to an ideal body weight. Second, you need to have some kind of estimate of the caloric intake that is necessary to maintain the animal at its current weight. Ideally, you would calculate this from what the cat normally eats. If this is not possible then you must use one of the published maintenance energy formulas. Beware if you do this. Often, due to distorted body composition, lack of exercise, or individual metabolic efficiency, your estimate will be higher than the cat's actual requirement.
Finally, you have to decide just how much caloric restriction you will have to impose on the cat to meet your goal. This can be calculated two different ways:
1. Feed the cat 60–70% of its current intake.
2. Calculate the cat's energy requirement at its ideal weight. Feed the cat 60–70% of its goal energy requirement.
Whatever method you decide to use, you will need to educate the client thoroughly, enlist his or her complete cooperation, and monitor the cat regularly (every three to four weeks) in order to achieve success. The cat should be weighed on the same accurate scale (preferably an electronic baby scale) regularly to evaluate its progress. You may need to adjust your recommendations if the cat is not losing weight effectively and you are satisfied that the client is in compliance or if the cat is losing weight too rapidly. The cat should not be losing more than 3% of its body weight/week.
There have been few published studies evaluating the efficacy of these methods. The ones, which were done in a controlled setting (e.g., a pet food company’s research facility), have been reasonably successful. One study (Gentry, 1993) that evaluated a weight loss program in client-owned dogs and cats was less successful. All five cats and 15 dogs that stuck with a ten month program (three cats and five dogs dropped out) lost weight. However, these animals only lost, on average, 34% of their goal. Another, more recent, investigation had much better results (Center, 2000). Twenty-eight pet cats considered > 20% overweight were put on a weight reduction program for 18 weeks. Four of the cats dropped out due to owner compliance issues. Of the remaining cats, all lost weight and 14/24 attained > 90% of their targeted weight loss during the 18 week study period.
There are a few reported studies on the safety of weight reduction regimens for cats. One study (Watson et al.) involved 21 cats estimated to weigh > 115% ideal body weight. The weight reduction regimens were calculated at either 60% or 45% of calculated energy requirement at a goal weight. The goal weight was estimated as 85% of the current weight and the energy requirement was estimated as 60(BWkg). These were cats housed in a research facility and they were fed a prescription feline weight reduction diet for 18 weeks. Both groups of cats lost weight and remained healthy with no signs of impending hepatic lipidosis. The 45% restricted cats lost more weight (25% of starting body weight vs. 18%) than then 60% restricted cats. The authors conclude that energy restriction to this degree is a safe and efficacious method of managing obesity in cats. This study suggests that concerns that exist about the risk of inducing feline idiopathic hepatic lipidosis by a weight reduction regimen in an otherwise normal cat may be exaggerated.
There has also been some preliminary investigation into the effects of l-carnitine on facilitating rapid weight loss in dogs and cats. L-carnitine is a co-factor of fatty acid metabolism. It is obtained through both the diet and synthesized de novo. Center et al., investigated the effects of supplementing l-carnitine (250 mg/cat) in a randomized double-blinded placebo controlled study involving two groups of obese pet cats that were placed on a rapid weight loss regimen for 18 weeks (see above). Cats in both groups lost significant amounts of weight with no adverse effects. The cats that received the l-carnitine lost weight at a slightly more rapid rate than the cats that received the placebo.
Tips for Success
There are several tactics you can use to motivate the client toward success with a weight-loss program. First, recognize that feeding a pet is often a bonding activity. You must give the client and the cat alternatives to feeding calorically dense foods and treats for this activity. They could substitute low calorie treats, games, or grooming for table scraps. Begging for food probably has as much a behavioral component to it as a hunger component and ignoring the behavioral aspects of feeding will doom your program to failure. Giving cat owners a prescribed treat allowance can work in some cases. Most people know how to count calories, so tell them how many calories a day they can give as treats, and give them an idea of the caloric content of the cat treats they use or some alternatives. This will give them some flexibility in how they give treats from day to day.
Second, it may be helpful to feed the cat three or four small meals a day rather than one or two large ones. Many cats are used to being fed free choice (which probably played a part in their weight gain to begin with) and object to being switched to scheduled meals. Using food puzzles or some other type of ploy to make a cat work for its food may help to decrease begging (or, as is generally the case with cats, demanding) and provide an opportunity for exercise. One possible solution to the all too common problem of cats waking their owners up in the middle of the night looking for food, is to use one of the timed feeding mechanisms so that food can be made available while everyone else is sleeping.
Multi-cat households pose a special challenge, since in order for the weight reduction program to be effective, the different cats in the household must be fed individual portions. Some cat owners cannot (or feel that they cannot) separate their cats during feeding times. Also, sometimes there is an individual cat in the household that really needs to be fed free-choice. If possible, the free-choice food should be put some place out of reach of the dieting cat (on a counter or in a crate that only the smaller cat can fit into).
There are a number of reduced calorie cat foods currently on the market. Many of these foods are low fat and contain increased amounts of fiber. They have been formulated to contain greater amounts of protein, vitamins, and minerals to compensate for caloric restriction and possible decreased bioavailability of these nutrients due to the high fiber content. The hypothesis is that the fiber will help to satiate the cat eating the food. How well this ploy works depends upon the individual. There have been a few studies published to date that have looked at the impact of high fiber foods on food intake of dogs. Two investigations (Jewell and Toll; Jackson et al.) found that increasing the fiber content of canine foods decreased voluntary intake while the other (Butterwick and Markwell) reported the opposite finding. The major difference between the studies was that the one investigation that found no effect of fiber tried to mimic a weight reduction scenario by restricting food intake while the other two investigations allowed the dogs eat their fill.
Finally, the question that many people have been asking is what impact does feeding cats commercial food containing large amounts of carbohydrate have on promoting weight gain. In recent years, there has been the advent of several popular diets for humans that advocate low or at least controlled intake of carbohydrates. The rationale, in part, for these diets is that glucose is the principal stimulus for insulin release which in turn acts to promote the storage of nutrients absorbed from the diet, particularly in the form of body fat. The “Zone Diet” for example advocates eating a combination of foods that will keep your insulin secretion within an optimal zone to promote fat burning as opposed to fat deposition. Despite glowing testimonials, evidence is lacking that shows that these diets work in any way other than resulting in overall lower caloric intake and creation of a negative energy balance.
Glucose is also a potent stimulus for insulin release in the cat although blood amino acid levels are also important in modulating the second phase of insulin secretion. In addition, cats lack the enzyme glucokinase in their hepatocytes and pancreatic ß cells and it is believed that the lack of this enzyme plays a role in the tolerance of dietary carbohydrate and insulin secretion in cats. Recognition of these unique aspects of feline metabolism has led to speculation that increased carbohydrate intake could trigger excess insulin secretion and this could predispose to the development of obesity and in some cases diabetes mellitus in cats. It is important to keep in mind, however, that while it is true that cats foods, in particular dry (extruded) foods can contain a substantial amounts of carbohydrate, any link between carbohydrate consumption and predisposition to obesity or diabetes mellitus in cats is still just a matter of speculation. This is an area of ongoing investigation at a number of institutions, and hopefully, we will have a better understanding of feline energy metabolism in the coming years.
In conclusion, while it is possible to safely and effectively diet overweight cats, as small animal practitioners we should be doing our best to educate the cat-owning public so that they prevent their pets from becoming overweight in the first place.
REFERENCES are AVAILABLE ON REQUEST