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  • UC Davis Vet School

Nutritional Management of Weight​​​​​​​

Overweight and obese pets are a growing concern among veterinarians. The abundant supply of highly nutritious and high calorie foods and treats, coupled with a less active lifestyle in many cases, inevitably results in the storage of the excess energy as fat. Over thousands of years, dogs and cats have been selected in part for their ability to efficiently accumulate this body fat in times of plenty in preparation for times of famine. Animals with the largest fat stores had the greatest likelihood of successfully surviving when food was scarce. Fortunately in the 21st century, we no longer undergo these once common periods of famine. Our pets are not adapted to this new era of constant feast and readily gain more and more fat. In fact, the excess of fat has become so commonplace that abnormally large accumulations of fat have become the accepted norm. Accumulations of fat over the ribs that prevent them from easily being felt and indistinguishable waistlines are often not recognized as cues that a pet is overweight or potentially obese.

Health Consequences of Obesity It is now known that overweight pets are at increased risk for developing many diseases such as diabetes mellitus, arthritis and breathing problems. In dogs it has been shown that they also have a shorter lifespan by up to two years. Thus, keeping pets lean can greatly improve both their quality of life and quantity of life. Few medical conditions with such severe adverse consequences can be so readily treated effectively. Veterinarians have become increasingly aware of the importance of weight management as a key component of preventative veterinary medicine.

Body Condition Scoring Prevention of obesity starts with close monitoring of every pet's amount of body fat through the use of a body condition score (BCS). A BCS is simply a number that describes the amount of fat that a pet has accumulated. Some systems use a 5-point scale and others use a 9-point scale. A BCS of 1 indicates that a patient is very thin and a score of 5 (5-point systems) or 9 (9-point systems) represents a patient that is obese. A patient that is a "3" (5-point systems) or a "4" or "5" (9-point systems) is an ideal body weight. Each point above or below 3 for the 5-point system is 20-30% over- or underweight, or 10-15% for each point above or below 5 on the 9-point system. Determining a pet's body condition score is much more useful than simply using their body weight as a guide to determine whether they are overweight since there can be a large variation in appropriate body weights for different sized pets. For example, it is difficult to know if a 65 pound Labrador Retriever or a 16 pound Maine coon cat are overweight, but if they each have a body condition score of 6 out of 9, we know that they are each approximately 10-15% overweight.

Tailoring Weight Loss Plans Pets that are overweight and at risk of becoming obese or pets that are already obese can benefit from a weight loss plan. Weight loss plans are designed to achieve steady weight loss while keeping the pet as comfortable as possible. It is generally recommended that pets lose no more than 2% of their body weight per week. Rates greater than 2% are associated with feeling (and acting) hungrier, a slowing of the pet's metabolism (making weight loss even more difficult), and preferential burning of muscle for energy rather than body fat. Consistently achieving this 2% rate of weight loss usually takes some tailoring. Surprisingly, some pets only need 50% of the calories calculated using body weight alone to maintain their weight while others need up to 50% more. Since there is such a large amount of variation from pet to pet, a veterinarian's best clue to the amount of calories that a specific pet needs is the pet's own current caloric intake. Getting an accurate and complete list of all foods and treats (a diet history) that the pet is currently fed allows the veterinarian to calculate the amount of calories the pet is receiving and to ensure that the weight loss plan does not excessively restrict or provide too many calories. There are occasions where a diet history cannot be completed. In those cases, the veterinarian uses the pet's current weight to create an initial recommendation. Whichever approach is utilized, the long-term success is completely dependent on following the pet's response to the recommendation. Even with the most accurate and complete diet history and the best calculations, the initial weight loss plan may not result in weight loss of around 2% of body weight per week and can even result at times in weight gain. Therefore, veterinarians use regular weight checks during the weight loss period to adjust the amount of calories fed to maintain a consistent rate of weight loss. It is not uncommon for pets just starting a program to need multiple weight checks to achieve the desired rate of loss. This period of adjustment is more common when a pet's diet history cannot be used for initial recommendations. This is why every attempt to determine a pet's current caloric intake is made prior to initiating a weight loss plan.

Diets for Weight Loss Since the amount of calories fed inherently must be reduced to result in weight loss, the volume of food will also need to be accordingly restricted if the pet's regular diet is to be used for weight loss. Veterinarians usually do not use a pet's current food for patient's undergoing weight loss in part to avoid this reduction in volume. The volume of food a pet receives has a direct effect on their sense of fullness (satiety). Smaller volumes do not distend the stomach as much and therefore can lead to the feeling of hunger. Therefore, most veterinarians initially choose to feed a special low calorie diet designed for weight loss and not the pet's regular diet. Most of these diets contain less calories per cup or can than a typical maintenance diet or even an over-the-counter "light" pet food. Switching the diet allows a similar volume of food to be fed while still reducing the amount of calories that the patient is receiving. These special weight loss diets have another advantage over a typical diet - almost all have increased amounts of essential amino acids, fatty acids, vitamins and minerals. Pets undergoing weight loss only need less calories, they do not need less essential nutrients. Feeding a typical maintenance diet in an amount necessary to cause weight loss places the animal at risk of developing multiple nutrient deficiencies. Pet food manufacturers design their food to contain a specific amount of a nutrient per calorie. If the amount of calories were to be reduced by 30%, then all of the nutrients are reduced by 30% as well. Although there is a small excess of each nutrient added for safety, the restriction in calories necessary for weight loss most often exceeds this safety margin, causing a standard diet to become deficient. Therefore, diets designed for weight loss are often prescribed to ensure that the pet feels as full as possible, as well as to ensure their nutritional requirements are met. A few diets designed for weight loss are not lower in calories but rather are lower in carbohydrate and higher in protein and fat to potentially change a pet's metabolism to utilize more fat. There are no published studies to date to support the use of these lower carbohydrate diets and they are usually used only when traditional, low calorie weight loss diets have failed.

Treats An equally important component of a pet's diet is treats. Treats provide a pet with feedback that they are important members of the family. Accordingly, veterinarians will often strive to include some treats in a weight loss plan. Although any treat can generally be fed, treats should be limited to no more than 10% of a pet's daily caloric intake. This decreases the potential of creating a nutrient deficiency since most treats are not complete and balanced foods. It can be surprising how many calories some treats contain compared to others. For example, 1 tablespoon of peanut butter has the same number of calories as 3 cups of air-popped popcorn without butter. Many people with pets are equally surprised to find out that pets will often eat lower calorie treats equally as well as those containing more calories.

Exercise An additional way to increase a pet's sense of being appreciated is to play or walk with them. This also has the added benefit of providing the pet with much needed exercise during weight loss, which assists with the burning of fat and the increasing of muscle mass. The use of laser pointers and feather toys to encourage stalking and predatory behavior in cats can be very useful in increasing activity. For dogs, retrieving thrown objects or taking them on progressively longer walks can be an effective means of increasing their activity.

Goal of Weight Loss Many people with pets wish to know what their pet's ultimate weight should be. Some veterinarians are reluctant to provide a weight because it focuses on a number rather than a meaningful measure of the pet's health. Achieving an ideal body condition score and/or an improvement in a health problem is a much more useful goal for most pets. For example, if a dog with arthritis that could barely walk around the block before weight loss is able to regain her ability to go on walks and play without as much pain, the program has been very successful regardless of the end weight. End weights can also be somewhat misleading as patients convert pounds of fat into pounds of muscle.

Weight loss plans end when the goals of the program have been achieved. That may in fact be a goal weight, but often that may be a body condition score or an improvement in a health problem. Regardless of the specific end point, success should be celebrated, and the habits and behavioral changes that achieved the weight loss should be retained for the rest of the pet's life.

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