When I was a veterinary student, I was taught that dietary fat and gastrointestinal disorders were often a bad combination. The rationale behind this had to do with the fact that fats are often considered to be the nutrient class that is most difficult to digest. Therefore, it’s not too surprising that many of the diets recommended for cats with digestive disorders are relatively low in fat.
I’m not sure what the foundation for this recommendation is. Perhaps some of the underlying facts were “borrowed” from human or canine physiology, but research casts doubts on the “fat as boogeyman” theory … for cats with chronic diarrhea, at least.
Scientists divided 60 cats with chronic diarrhea into two groups. One group was fed a low fat diet (24% of calories) and the other a high fat diet (45% of calories) for six weeks. Over that time, the owners kept track of the consistency of the cats’ feces. They used “an illustrated fecal score chart ranging from 0 (very watery) to 100 (firm and dry).”
According to the researchers:
Fecal scores improved significantly, with 78.2% of cats improving by at least 25 points on the 100-point scale or having a final fecal score of at least 66. Over one third of the cats developed normal stools. There were no differences in clinical responses between the diets. Clinical improvement was noted within the 1st week, and maximized within 3 weeks.
Interesting. So it appears that dietary fat content is not all that important of a consideration when it comes to improving chronic diarrhea in cats. So why did cats eating both high and low fat diets get better in this study? I think it’s because both the high and low fat diets were highly digestible.
Digestibility is a term that gets thrown around a lot in pet nutrition circles, but its actual meaning is not always well understood. Simply put, the portion of a food that is digestible is that which is absorbed into the body. The indigestible parts of the diet are eliminated from the body in the feces.
Pet food manufacturers can put a number to digestibility through feeding trials. For example, if a cat eats 50 grams of food per day and produces 5 grams of poop per day she is absorbing 45 grams of the food into her body.
45 grams/50 grams x 100% = 90%
This food is 90% digestible. (We’re ignoring water for the sake of simplicity, which is fine as long as we don’t try to compare dry and canned foods.)
You will not find actual numbers for digestibility on pet food labels, but if you call the manufacturer, they should be able to give them to you. Digestibility percentages of around 85-90% are a good starting point for cats with chronic diarrhea. Alternately, look for the terms highly digestible or low residue on the label (you’re most likely to find them on prescription diets). Unlike many phrases you find on bags and cans of cat food, these actually mean something.
Dr. Jennifer Coates
Effect of diets differing in fat content on chronic diarrhea in cats. Laflamme DP, Xu H, Long GM. J Vet Intern Med. 2011 Mar-Apr;25(2):230-5.