Claudia A. Kirk, DVM, PhD, DACVN, DACVIM
Obesity is the most important malnutrition of companion animals. It can be a disabling medical condition when moderate to severe in scope. At current prevalence rates between 33–60%, pet obesity must be considered a significant hazard to dogs and cats. Increased emphasis on preventative health programs makes obesity prevention an important aspect of health maintenance programs for dogs and cats. Prescribing a successful, long term weight loss and maintenance program usually requires management of multiple, inter-related patient and client factors. In companion animals as in human medicine, obesity prevention is significantly easier than reversal.
Obesity is a condition of positive energy balance and excess adipose tissue accumulation with adverse effects on quality and quantity of life. While variable definitions exist, obesity is generally defined as body weight 20% above ideal weight due to the accumulation of excess body fat. Typical body fat content of normal lean animals is between 15–25% body fat. Body condition scoring systems are validated to the proportion of body fat with animal at 25–34% considered overweight and those at and above 35% body fat obese.
Pathogenesis of Body Fat Accumulation
The pathogenesis of obesity is not as simple and direct as uncontrolled gluttony. Obesity is a complex disorder of energy metabolism and satiety control with significant genetic components. Multiple genetic and environmental factors control regulation of food intake, resting metabolic rate, thermic effect of food, and energy expenditure and efficiency during work. Three common causes of obesity in pets are overeating, decreased exercise, and lower metabolic rate; however, genetic influence cannot be overlooked.
Identifying Risk Factors for Obesity
To develop a rational obesity prevention program for individual animals, the veterinarian first should identify obesity risk factors within the animal and environment. Risk factor evaluation begins with a nutritional assessment at each veterinary visit per the WSAVA Guidelines for Nutritional Assessment.
Risk factors associated with a specific age, gender, breed or housing cannot be eliminated but should serve as starting point for a tailored nutritional plan and ongoing monitoring. Other factors such as high fat diet and inactivity can be addressed early on. Neutering results in a significant risk for obesity, particularly in male cats and female dogs. Limited exercise with indoor housing may be addressed with owner-induced play or planned exercise in both dogs and cats.
Effect of Neutering
Neutering has been shown to reduce the daily energy requirement (DER) of adult cats by 24–33% compared to intact control cats. The decrease in DER does not appear to be influenced by age at neutering. Reduced energy requirements have also been noted in neutered dogs. The reduction in energy requirement is most likely attributable to a reduction in basal metabolic rate and/or increase drive for food intake. The mechanism of reduction in basal metabolism following neutering may be related to reductions in lean body mass or changes in thermogenic activity within the liver. The role of altered feedback inhibition of androgens on leptin has been suggested as a mechanism of increased food intake. Because reduction in DER without reduction in food intake will lead to obesity, it is imperative nutritional counseling is provided to owners at the time their pet is neutered. Owners need to control food intake and monitor BCS after neutering and be prepared to reduce intake at the first sign of weight gain.
Accurate Estimate of Ideal Body Weight and Caloric Needs
Weight and body condition score can be used together to more accurately determine ideal body weight. Ideal weight should be identified prior to the onset of obesity. Accurate identification of ideal weight helps to set acceptable boundaries for weight range and better estimates of daily energy requirements.
Accurate Estimate of Energy Requirement
Providing owners with target caloric intake can help establish a pattern of owner compliance with feeding plans. RER can be calculated using several well established formulas. We use: RER = 70 x WtKg0.75 using the ideal body weight in the calculation. Maintenance energy requirements (MER) are calculated from the RER multiplied by an activity factor. This factor is about 1.2 for a normal lean housecats and 1.4–1.6 for low-moderate activity dogs. These calculations should be considered a starting point and will not work in all animals. Ideally, establishing caloric intake needed to maintain ideal weight is best determined by a diet history and simple calculations. Educating clients as to their pet's individual ideal weight and energy needs sets the stage for long-term dietary compliance.
Feeding excess treats, table scraps and free choice feeding methods increase the risk of obesity. Because owners enjoy the human-pet interaction of treating or may use treats as training rewards, incorporating treats at 10% or less of total calories may be considered. Treats may include hand-fed regular diet, low calorie foods (carrot round, popcorn, or cooked vegetable) or limited commercial treats.
Food composition and food form may influence total caloric intake in dogs and cats. Cats consume more calories when fed dry commercial foods compared to canned foods. Dogs tend to have an increased appetite when fed canned and improved satiety when offered high protein/high fiber foods. Food ingredients that increase bulk (i.e., fiber and water) may help control caloric intake either through satiety or owner visual cues. An ideal nutritional profile has not been established. While low carbohydrate foods may be beneficial in some animals, the smaller food portion and higher fat levels may promote begging or weight gain over low calorie options.
Controlling caloric intake is key to obesity prevention for most animals. Two recent studies have identified challenges to controlling food intake. Owners were found to feed larger portion sizes to pets when using a larger feed scoops or food bowls compared to smaller feeding utensils. Even with the use of graduated measuring cups, food portions were unreliable compared to weighed food portions using a kitchen scale. Minor variations in food intake can lead to weight gain over time, particularly in the obese prone pet.
Food competition and multipet households present unique challenges to controlling food intake. Food competition often increase caloric intake in dominant animals as does unsupervised feeding of multiple pets. Helping owners provide individual food portions through adjusted feeding practices may be required.
Compliance can be enhanced by altering the external and internal factors that influence the desire to eat. The external factors are psychological, social and food related (palatability and feeding method). Most of the internal factors relate to the food itself and its presence in the GI tract. Chemical, neural and mechanical satiety signals influence the desire to eat and may promote behaviors, like begging. Despite conflicting data, increasing fiber in the diet is one effective means of decreasing voluntary food intake and the desire to eat, particularly in dogs. Dogs tend to be bulk feeders and here is where fiber can help. Feeding a single flavor of high moisture content canned foods seems to help in cats. Higher protein and low carbohydrate intake may help promote satiety in some animals by two proposed mechanisms: 1) Protein and fat stimulate increased release of CCK from the gut. CCK acts both peripherally and centrally to prolong a feeling of satiety; 2) Increased CNS concentrations of BHB associated with fat metabolism increase the relative neuronal satiety mediators both directly and indirectly.
Dividing the daily food allotment into multiple meals and appropriately timing these meals can influence hunger and the owner's perception of their pet's hunger, as well as waste a few calories via the thermic effect of food. Client education and assistance in working through the behavioral problems that may come from food seeking behavior is one of the most important aspects of successful weight control. Ongoing monitoring using regular nutritional assessments is important. During weight loss, we reassess progress initially every two weeks and then monthly for the duration of the weight loss program. For a preventative program, review progress according to the risks for obesity, but no less than annually.
Regular exercise expends energy, builds and maintains lean muscle mass and reduces boredom-related eating in people and in pets. Providing scheduled exercise, enrichment toys, or devising methods to capitalize on food seeking activities during feeding can result in weight loss in dogs and cats without further reduction of calories.
An owner's relationship to food or their pet may represent a significant risk factor for pet obesity. Owners who humanize their pet were much more likely to overfeed compared to typical pet owners. Client education, providing a nutritional and exercise plan, and identification of nutritional risk factors can help owners achieve compliance in maintain a healthy weight for their pet.
Prevention of obesity requires a regular nutritional assessment, a sound nutritional plan, and ongoing monitoring throughout the pets life. Early identification of obesity risk factors and client education will help assure success.
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