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