A couple of weeks ago we talked about how, unlike many other species, cats need more protein when they enter their golden years (around 12 years of age). In the process of researching that article I came across some disturbing information. The recommendations for minimum protein levels in cat food put forth by the Association of American Feed Control Officials (AAFCO) and the National Research Council (NRC) may be too low.
The NRC’s recommended allowance for protein in adult cat food is 50 g/1,000 kcal metabolizable energy (ME). For kittens, it is 56.3 g/1,000 kcal ME. Now don’t go looking for these sorts of numbers on cat food labels, they’re not there. What does appear on the label is the minimum protein percentage; this is an AAFCO number. The least amount of protein allowable in AAFCO-approved cat foods is 26% for adult maintenance and 30% for growth and reproduction (on a dry matter basis). The AAFCO and NRC numbers are related in that AAFCO uses NRC guidelines to come up with their recommendations.
Research published in 2013 looked at how much protein is needed for cats to maintain their lean body mass (LBM) versus how much is necessary to maintain their “nitrogen balance.” The equation for nitrogen balance is essentially the amount of nitrogen taken in minus the amount of nitrogen lost from the body. A negative nitrogen balance (more lost than taken in) is obviously an unsustainable situation and is associated with protein-losing conditions or malnutrition.
Twenty-four adult, neutered male cats were included in this study. For one month, all of the cats ate a 34% protein diet. After this baseline period, the cats were fed a low protein (20%), moderate protein (26%), or high protein (34%) diet for two months. The results revealed that only 1.5 g protein/kg body weight was needed to maintain the cats’ nitrogen balance, while 5.2 g protein/kg body weight was necessary to avoid a loss in lean body mass. The authors concluded that:
This study provides evidence that nitrogen balance studies are inadequate for determining optimum protein requirements. Animals, including cats, can adapt to low protein intake and maintain nitrogen balance while depleting LBM. Loss of LBM and an associated reduction in protein turnover can result in compromised immune function and increased morbidity [disease]. Current Association of American Feed Control Officials (AAFCO) and National Research Council (NRC) standards for protein adequacy may not provide adequate protein to support LBM. The minimum daily protein requirement for adult cats appears to be at least 5.2 g/kg (7.8 g/kg(0.75)) body weight, well in excess of current AAFCO and NRC recommendations.
The take home message from this study? Most cats should be eating foods that contain significantly more protein than the minimum currently put forth by AAFCO. A precise number is hard to recommend, but personally I look for dry foods with at least 30% protein supplemented with a 40-50% protein canned food. When cats have access to both, they are very good at balancing their own diets.
Discrepancy between use of lean body mass or nitrogen balance to determine protein requirements for adult cats. Laflamme DP, Hannah SS. J Feline Med Surg. 2013 Aug;15(8):691-7.