Diet and Body Condition

The 2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats provide comprehensive recommendations for canine and feline nutritional management.²⁴ Senior pets may have changing energy and nutrition requirements and may experience muscle or overall weight loss due to changes in the senior body such as immunosenescence, inflammaging, or a disease process. Evaluation of muscle and body condition scores can help monitor normal aging and age-related disease changes and determine when nutritional adjustment may be needed. Maintenance energy requirements (MER) generally decrease over a dog’s lifetime. MER decrease in cats up to age 10, after which they start to increase.^25–27 However, published data on the effects of age on energy requirements are extremely variable in cats. Calorie-restrictive diets have been shown to increase dogs’ longevity,²⁸ with an ideal body condition score (BCS) of 4.5 to 5 out of 9. A cat’s ideal BCS, up to 6 out of 9, can be associated with increased longevity, with underweight cats having greater morbidity and mortality risks.²⁹

Senior cats may be less able to digest and utilize nutrients. Decreased food digestibility may contribute to weight and muscle loss. Proteins are less digestible in 20% of cats older than 11 yr, and fats are less digestible in up to 33% of cats.³⁰ Food digestibility may be less of an issue with dogs.^31,32 In a recent study, adding moisture to foods increased the digestibility of nutrients in senior dogs.³³

Reduced protein synthesis and increased turnover of proteins may contribute to the loss of lean body mass (LBM) in senior pets.³⁴ Sarcopenia is the anticipated loss of LBM with age, with up to 33% loss in cats from 10 to 15 yr of age.³⁰ Dogs tend to lose LBM and gain fat as seniors and incur overall weight loss with advanced age.³⁵ Senior pets, particularly cats, may need up to 50% more protein to improve or slow muscle loss.³⁴ Cachexia may also be present and refers to weight loss with excessive LBM loss due to severe or chronic disease, such as chronic kidney disease, heart disease, and neoplasia.

Senior pets may also develop obesity, which is more common in dogs. Increased BCS and obesity are known to affect mobility and contribute to inflammatory processes and diseases. Poor mobility and decreased activity are assessed in frailty scores and are associated with a shorter time to death.³⁶

Healthy Senior Nutrition

The Association of American Feed Control Officials does not currently have guidelines for senior nutrition. However, senior dogs have decreased MER and need less caloric density and more fiber to optimize BCS. A senior diet may include mild increases in protein content and quality to compensate for LBM loss.³⁷ Healthy senior cats may require higher-caloric-density, higher-protein diets with increased digestibility and enhanced palatability fed in smaller amounts more frequently to help them maintain adequate muscle and body weight.³⁴