Introduction

    In Canada today it is estimated that at least 20% of cats are overweight and 5% are obese, a risk factor for diabetes mellitus, skin problems, and lameness. Middle-aged obese cats have a 2.7-times greater risk of mortality than cats at optimal body weight.

One consequence of obesity in cats is abnormal insulin secretion and these 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.

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 great 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, but your veterinarian will need a thorough dietary history in order to devise a successful weight reduction program.

The first thing to do before embarking on a weight loss program is to have a complete physical exam at your veterinary clinic. 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 bring a complete recipe. Does the cat has access to the food fed other cats in the household, are other family members feeding the cat (especially small children), and does the cat roam to beg, hunt, or scavenge food? It may be impossible to quantitate the cat's energy intake from this information, but it will alert your veterinarian to possible problems you may face in implementing the weight loss program. You may have to keep a food diary for a few days before you 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 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 your veterinarian must use one of the published maintenance energy formulas.

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 it is important to 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 feeding amounts if the cat is not losing weight effectively or if the cat is losing weight too rapidly. The cat should not be losing more than 3% of its body weight/week.

There has 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 mainly through the diet as a special additive in some premium brands and investigators found that supplementing l-carnitine (250 mg/cat) causes cats to lose weight at a slightly more rapid rate.

Tips for Success

    Feeding a pet is often a bonding activity. You must find alternatives to feeding calorically dense foods or treats for this activity. You could substitute low calorie treats, games, or grooming, for feeding 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. Having a prescribed treat allowance can work in some cases. Knowing how many calories a day you can give as treats, and the caloric content of the cat treats used or some alternatives will give some flexibility in how you 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 a prescribed amount of 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.

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, it is far better to prevent your pet from becoming overweight in the first place.

Bill Golbeck BSc DVM