Way off topic: How many calories am I feeding my cat?

You may be asking: Why is Len Feldman writing about cat food? The reason is that I've stumbled onto a problem that a lot of people are likely to have with their cats and dogs, and in finding an answer, it might help others. My cat, KayTee, recently developed Type 2 diabetes because I've been giving her too much food. To be more precise, she sees me as a box that dispenses Mars's Temptations treats whenever she pushes my handle (yells at me). So, in addition to putting her on insulin (Sanofi's Lantus, which seems to be the most effective for cats), her vet had me switch her food to a Purina Veterinary Diet formula, DM (Dietary Management,) from Purina's Fancy Feast Chicken & Turkey dry food. (She only eats dry.) Unfortunately, everything is expensive--Lantus is $200 or more per bottle, depending on where I buy it, her syringes are around $25 per 100, and the DM food is over $30 a bag for 10 lbs.

I'm running out of her DM, and I temporarily can't buy another bag, but I do have a lot of the Fancy Feast left. The question is, can I safely substitute the Fancy Feast for the DM? While in some cases, veterinary foods are prescribed to address urinary, kidney or gastrointestinal problems, in this case the primary issue is regulating caloric intake. So, if I can match the calorie count of Fancy Feast to that of DM, I should be close enough for temporary use. (I'm not suggesting that you do this permanently, only in an emergency.) But, here's the problem: Purina publishes the calorie content of many of its pet foods, but not Fancy Feast--not on the bag, and not online. So, how can I figure out how much Fancy Feast to substitute for the DM?

It turns out that there are two methods:

1. Pet Obesity Prevention has published a list of dry cat foods with their calorie content per cup as a downloadable PDF file. This document lists hundreds of foods and flavors from dozens of different brands, so you may find your cat's food on the list. However, Fancy Feast isn't on the list.
2. All pet food manufacturers are required to publish standards for their foods for protein, fat, fiber, moisture, and (if relevant) ash. These numbers are provided in two forms: A "Guaranteed Analysis," and numbers calculated using Federal standards. The Federal standard numbers are more accurate, but the Guaranteed Analysis numbers can be used if the Federal numbers aren't available. Plug the numbers into an online calculator provided by the Feline Nutrition Awareness Effort, and it will tell you approximately how many calories your cat food has, per 100 grams and per ounce. Purina states the calorie count of its foods in cups, so multiply the per ounce value by 8 to get the calories per cup.

In my case, DM dry has 592 calories per cup. When I plugged the numbers for Fancy Feast into the calculator and multiplied the per ounce value by 8, I came up with 960 calories. (Which might explain why Purina doesn't list the calories on the label.)  Next, I took my vet's instructions to feed KayTee a half-cup of DM a day. 592/960 is about 62%, meaning that I should feed KayTee only 62% as much Fancy Feast per day to give her the same number of calories as DM. That works out to just under 1/3rd of a cup a day. So, instead of feeding her 1/4 cup of DM twice a day, I'll feed her 1/3rd cup of Fancy Feast once a day.

Again, I don't recommend that you do this other than as a temporary measure, and I definitely don't recommend that you do this if your cat has been prescribed food to treat conditions other than overweight or diabetes, because those prescription or veterinary foods have (or don't have) specific ingredients based on your cat's condition. In that situation, calorie counts alone are largely irrelevant. However, this exercise is helpful, even if you've got an overweight cat and you want to find a cat food with fewer calories, or if you need to bulk up an underweight cat.