Obesity: the skinny on fat (Proceedings)
Obesity is the most important malnutrition of companion animals. It can be a disabling medical condition when moderate to severe in scope. At prevalence rate estimates of 10-40%, obesity must be considered a significant hazard to dogs and cats. Increased emphasis on pet health and preventative health programs makes obesity prevention an important aspect of health maintenance programs in dogs and cats. Treatment for obesity varies from frustrating to rewarding and evaluating and prescribing for successful, long term weight loss and maintenance usually requires management of multiple, inter-related patient and client factors. Diagnosis of disease secondary to obesity and the major task of client education and motivation is the provenance of the veterinarian.
Obesity is a condition of positive energy balance and excess adipose tissue accumulation with adverse effects on quality and quantity of life. Obesity literally means increased body fatness, but measurement of fat fractions of body composition is difficult in practice. Therefore, obesity can be defined as body weight in excess of 15 to 20 % of ideal, due to the accumulation of body fat. Negative health manifestations often begin at this level of weight excess and are a virtual certainty at a 30% excess over ideal weight.Pathogenesis of body fat composition
Pathogenesis of obesity is not as simple and direct as uncontrolled gluttony. The idea of human obesity as a syndrome caused by being "weak in will" has yielded to observations and reasoning that obesity is a complex disorder of 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 causes of initial obesity in pets are overeating, decreased exercise, and lower metabolic rate; however, genetic influence cannot be overlooked.
Risk factors for obesity
Gender is important in the development of adult obesity; females or neutered animals are more frequently affected with obesity than males or intact animals. In addition to gender, certain breeds are predisposed to developing obesity while other breeds appear to be resistant. Pet owner lifestyle is important, as overweight human beings are more likely to own an overweight pet. Apparently overweight owners provide opportunities that override normal internal and external satiety control signals for both themselves and their pets. Ad libitum feeding, improper meal feeding, inappropriate diet selection, supplementation, provision of home cooking, and the conditioning of abnormal feeding behavior all cause excess calorie consumption. Begging, competitive eating with other pets and specific food addictions are problems in some homes and are identifiable risk factors.
Body fat deposition
Body composition of 1-2% fat at birth increases rapidly to 10-15% by weaning at 4-6 weeks, and is 15-20% in normal dogs during the first year of maturity. Females have increased levels when compared with males. Twenty-five to 30% fat is normal in dogs 8-10 years of age as there is lower lean body mass and increased adiposity with ageing. The initial phase of obesity occurs during chronic, positive energy balance. A phase of static obesity follows when caloric expenditure equilibrates with intake and the animal maintains a stable, but altered body composition of increased adipose tissue. These phases may repeat many times during an animal's life leading to a gradual step-wise increase in body weight and body composition. Because fat-free mass appears to be an important determinant of resting energy, as more fat mass is acquired and as lean mass is lost, less energy intake is required to maintain the increased body weight (increasing fat mass). This explains why many obese animals do not appear to be eating "too much" or why owners often say "but my dog only eats a half of a cup of food a day".