It is generally accepted that the prevalence of overweight and obese pets has increased in recent years. Excess weight is the most common medical condition in companion animals and has a number of health and wellness implications for both pets and their owners.

Certain behaviors predispose dogs to weight gain. In Part 1 of this two-part series, we explore common causes of weight gain in dogs and the consequences of dogs being overweight or obese. In Part 2, we discuss treatment and monitoring strategies.

DEFINING OVERWEIGHT AND OBESE

Obesity is defined as excessive white adipose tissue.1 Human epidemiologic data show increased morbidity and mortality with increasing body fat mass.2 The most commonly used measure of body fat in people is the body mass index (BMI: weight [kg] divided by height2 [m]). People are defined as

• Underweight (BMI < 18.5)
• Normal (BMI = 18.5 to 24.9)
• Overweight (BMI = 25 to 29.9)
• Obese (BMI = 30 to 39.9)
• Extremely obese (BMI ≥ 40).3-6

Individuals who are overweight or obese have an increased risk of cardiovascular disease and certain cancers and of overall mortality.7-10

Data from companion animals are more limited, and the definition of obesity is more arbitrary. Dogs are overweight when their weight is > 15% above ideal and are obese when their weight is > 30% of ideal.11,12 However, these criteria have not been confirmed with rigorous epidemiologic studies, and limited data exist on the definition of an optimal body weight. In most animals, obesity results from an imbalance between energy intake and energy expenditure.

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