Animal Tissue and Anatomy

Energy consumed by an animal is lost through feces, urine, methane gas production, heat increment during digestion, and physical movement. Only the remaining net energy is available for maintenance and production.

Pigs are monogastric (single-stomached) animals, meaning they cannot synthesize certain essential amino acids like ruminants can. Consequently, their rations must be specifically supplemented with essential amino acids such as lysine and methionine to support proper growth and development.

A slightly elevated body condition score (BCS of 6-7 out of 9) provides a nutritional reserve that can be protective in chronic diseases associated with cachexia, such as cardiac disease, renal disease, and cancer. This phenomenon is often referred to as the obesity paradox in veterinary medicine.

For canine weight loss diets, the recommended protein concentration is typically greater than 80 g/1000 kcal to preserve lean body mass. A target of more than 100 g/1000 kcal is generally reserved for feline weight loss diets, which have higher protein requirements.

Feline weight loss diets require a higher protein concentration, typically greater than 100 g/1000 kcal, to prevent the loss of lean body mass. A target of 80 g/1000 kcal is insufficient for cats undergoing weight loss, though it is appropriate for dogs.

According to AAFCO guidelines, a canned (wet) pet food can be labeled as 'low calorie', 'light', or 'lite' if it contains less than 900 kcal/kg for dogs and less than 950 kcal/kg for cats.

For dry pet foods, AAFCO regulations state that 'light', 'lite', or 'low calorie' diets must contain less than 3,100 kcal/kg for dogs and less than 3,250 kcal/kg for cats.

Therapeutic weight loss diets are formulated to be nutrient-dense so that when calories are severely restricted (such as when energy requirements are under 80% of RER or when a pet needs to lose more than 20% of body weight), the pet still receives all essential nutrients.

The safe and ideal rate of weight loss for both dogs and cats is 1% to 2% of their body weight per week. Losing weight too quickly can lead to loss of lean body mass and, in cats, increases the risk of hepatic lipidosis.

For obese cats, the initial caloric target is typically set at 80% of the Resting Energy Requirement (RER) calculated for their goal (ideal) body weight. This conservative restriction helps ensure safe, steady weight loss while minimizing the risk of hepatic lipidosis.

Cats generally have a lower maintenance energy requirement (MER) per kilogram of body weight compared to dogs. This is due to differences in metabolic rate, body composition, and activity levels between the two species.

If the current caloric intake is unknown, the initial Daily Energy Requirement (DER) for weight loss is typically set to the Resting Energy Requirement (RER) for the patient's goal weight. This provides a safe baseline to initiate weight loss.

If the owner has been accurately measuring and reporting the pet's current caloric intake, a standard and safe starting point is to reduce that intake by 20% to initiate weight loss.

L-carnitine plays a key role in fatty acid metabolism by facilitating the transport of long-chain fatty acids into the mitochondria for beta-oxidation. It also has potential anti-inflammatory properties in various disease states. However, clinical evidence regarding its efficacy for weight loss in obese pets remains limited, meaning more data is needed before recommending its widespread use for obesity.

Fiber is indigestible or only partially digestible, meaning it provides very little metabolizable energy while adding bulk to the diet. This bulk dilutes the caloric density of the food, allowing pets to consume a satisfying volume of food while consuming fewer total calories.