Question
At the pet store this weekend, we were approached by a sales representative marketing a "gourmet" pet food brand. One of the biggest selling points was apparently that the food contains "wholesome whole grains, garden veggies and healthy fruit", in addition to meat.
While I understand that vegetable products such as corn meal are frequently used as fillers for dry pet food, I question the value of fruits and vegetables being added to cat food, since cats are obligate carnivores.
The main selling point was that the first ingredient on the list of each of their foods were "real meats" (as opposed to meat by-products), so presumably the food contains enough crude animal proteins to meet the cats primary dietary requirements, but does adding fruit and vegetables have any actual health benefits to a cat? Or is it just a marketing gimmick, playing on people's assumption that if the food sounds appealing to them, it might be more appealing to their cats?
Answer
Most of the relevant work seems to indicate that the nutrients found specifically in vegetables/fruits aren't digestible by cats, and the nutrients that they need are found in animal tissue (usually muscle or fatty tissue). So the inclusion of these ingredients in their food is not poisonous, but adds indigestible mass that they don't need.
For example, in The carnivore connection to nutrition in cats (JAVMA, Vol 221, No. 11, December 1, 2002) Dr. Debra L. Zoran states:
Vitamin A is found naturally only in animal tissues, and it must be provided as the biologically active form in diets formulated for cats because of the fact that cats cannot convert β-carotene (which is plentiful in plants) to retinol (the active form of vitamin A); this conversion is not possible, because cats lack the necessary intestinal enzyme.
In high enough levels, being unable to digest some materials can actually be harmful to the cat. For example, benzoic acid is one of the components in cranberries (a popular fruit to add to cat food because of its folklore status as a cure for urinary tract infections in humans). Too much benzoic acid can be fatal for cats.
Outbreaks of poisoning affecting 28 cats have followed ingestion of meat containing 2.39% benzoic acid. The effects were nervousness, excitability, and loss of balance and vision. Convulsions occurred and 17 cats either died or were killed. Autopsies showed damage to intestinal mucosa and liver. The sensitivity of the cat may be due to its failure to form benzoyl glucuronide and toxicity may develop with quantities greater than 0.45 g/kg single doses or 0.2 g/kg repeated doses (Bedford & Clarke, 1971).
However, you'd have to feed your cat a LOT of cranberries to get to this level of toxicity, so I don't believe your cat would be in any danger from a commercially produced food that included cranberry.
Cranberries are somewhat of an unusual case. Their inclusion is often to promote urinary health, not just to increase the "nutritiousness" of the food. Skepvet summaries his findings:
There is weak theoretical justification for using cranberry products for UTIs, though none of the supporting preclinical evidence involves dogs or cats. There is conflicting clinical trial evidence in humans, and no clinical studies in dogs and cats. There are weak theoretical safety concerns.
Peas and pumpkin can also be included not for nutritional value, but to bulk up the stool and relieve constipation. I don't generally recommend feeding fiber to an otherwise healthy cat and prefer to monitor the situation myself. GI symptoms can be the first sign of an illness, so I prefer to know as soon as possible that something may be wrong.
Answered By - Zaralynda