Q&A with Sally Perea, DVM, MS, DACVN (sponsored by Iams)

Q: How does aging affect protein metabolism in dogs and cats?

A: With age, we see a decline in protein turnover and synthesis that can result in loss of lean body mass.1 In a study by Hayek and Davenport, a loss of lean body mass was seen in both older dogs and cats.2 The data showed that young cats had a lean mass of 69%, while cats older than 7 years had a lean mass of 64%. Young dogs had a lean mass of 79%, while dogs older than 7 years had a lean mass of 70%. Veterinarians see this clinically when they notice older pets losing muscle mass as they enter their senior years.

Sally Perea

Q: How do age-related changes in protein metabolism affect the protein needs of healthy older dogs and cats?

A: When considering minimal protein needs, studies have shown that older dogs require about 50% more protein than younger dogs do. This was demonstrated in one study that compared protein requirements of senior dogs (12 to 13 years old) with those of younger counterparts (1 year old).3 Young dogs were more efficient, requiring 0.4 g of nitrogen/kg body weight/day to replace liver and muscle protein reserves versus 0.6 g nitrogen/kg body weight/day in senior dogs.

In another study, young adult and senior dogs were fed foods that contained 16% or 32% protein, supplied as either chicken or chicken plus corn gluten meal.4 After seven weeks of feeding, the senior dogs that were fed the 32% protein diet had increased percent lean body mass compared with senior dogs that were fed the lower-protein diet. The younger dogs did not show a change in lean body tissue in response to the increase in dietary protein.

Therefore, it is important to maintain protein intake in aging pets to help ensure that their amino acid requirements are met for repair of tissues, support of the immune system, and ability to respond to stress. This becomes especially true as we consider that aging pets often start to decrease food intake and, thus, protein intake because of lower energy needs. Therefore, I always recommend that senior pets be fed diets that provide slightly boosted protein levels compared with adult maintenance formulas.

Q: Is there any evidence that healthy older dogs and cats benefit from being fed lower protein levels?

A: No, there is no evidence to suggest that lower protein levels should be fed to older pets. In the past, this approach had been taken because it was thought that it might help address early renal disease in older pets. However, reducing protein intake does not protect senior pets from developing renal disease, and unnecessarily restricting protein may have other negative effects such as loss of muscle mass.5

Sally Perea earned her DVM and Master's in nutrition degrees from the University of California, Davis (UCD). She is board-certified by the American College of Veterinary Nutrition. She has worked as a principal veterinary nutrition consultant for Davis Veterinary Medical Consulting, served as an assistant clinical professor at the UCD School of Veterinary Medicine, and was senior nutritionist at Natura Pet Products. She is currently a senior scientist for P&G Pet Care R&D.

References

1. Richardson A, Birchenall-Sparks MC. Age-related changes in protein synthesis. Rev Biol Res Aging 1983;1:255-273.

2. Hayek MG, Davenport GM. Nutrition and aging in companion animals. J Anti Aging Med 1998;1:117-123.

3. Wannemacher RW, McCoy JR. Determination of optimal dietary protein requirements in young and old dogs. J Nutr 1966;88:66-74.

4. Davenport G, Gaasch S, Hayek MG, et al. Effect of dietary protein on body composition and metabolic responses of geriatric and young-adult dogs. J Vet Intern Med 2001;15:306.

5. Laflamme, DP. Pet food safety: dietary protein. Top Compan Anim Med 2008;23(3):154-157.