By: Wendy Simpson DVM
Everyone is concerned these days about what to feed their cats. It can be very overwhelming and hard to understand when you start reading the labels. We will explain how to analyze the nutritional composition of a bag or can of food.
Cats are metabolically designed to utilize protein and fat as their primary sources of energy. In the wild cats eat rodents and birds composed of mostly fat and protein and the only carbohydrates ingested would be the plant material that is in the gastrointestinal tract. Cats have a very limited ability to process carbohydrates. In fact, they can only utilize up to about 10% of their diet from carbohydrates and any surplus is stored in the body as fats.
Cat foods are typically in either a dry kibble form or a wet canned form. Foods consist of water, protein, fat, carbohydrates, and other supplements such as vitamins and minerals. Most cat food labels list their nutritional value on an “as fed basis” that includes the moisture level. However, because the water content can vary dramatically between diets from less than 5% to more than 80%, we have to remove this component so we can compare them on the same moisture level. This is called a “dry matter basis” and this allows you to analyze all types of food in the same level. The pet food labels are always listed on the box or the bag on an as fed basis. To get the information on the dry matter basis, you can call the pet food companies and ask for this information or you can analyze the label on the package yourself. To convert a label with the “as fed” information to a “dry matter” basis, we just need to remove the water component.
Brand A Canned Food
Guaranteed Analysis (from label)
Crude Protein: Min 11%
Crude Fat: Min 4%
Crude Fiber: Max 1.5%
Moisture: Max 78.0%
Net weight: 85 grams (3 oz can)
Brand B Dry Food
Guaranteed Analysis (from label)
Crude Protein: Min 32%
Crude Fat: Min 16 %
Crude Fiber: Max 4.5%
Moisture: Max 10%
Net Weight: 454 grams
Brand A is 78% moisture or water and the can’s net weight is 85 grams. Since 78% of that 85 grams is water, that means that the remaining 22%, or 18 grams, is the rest of the nutrients. The dry matter composes therefore 22% of the total can.
Brand B dry food is 10% water and the bag weight is 454 grams. That means that the reaming 90% of the bag or 408 grams is the rest of the nutrients. So, the dry matter composes 90% of this diet.
Now that we have this information, we can start to compare the nutrient levels of the two foods. Let’s start with protein. Looking at the label as is, it looks like the Brand B dry food has three times more protein at 32% than Brand A canned food which has only 11%. If we take out the water component, we can compare the protein on the same level.
To compare the protein levels on a dry matter basis, we take the protein and divide it by the percentage of dry matter in each food.
Ex. Brand A canned food protein content = 11 (percent protein) / 22 (dry matter) = 50%
Ex. Brand B dry food protein content = 32 (percent protein) /90 (dry matter) = 35%
The canned food has the higher protein count than the dry food once they are compared on a dry matter basis.
You can repeat this to analyze the fat and fiber percentages as well. You may then notice that these numbers don’t add up to 100%. What is remaining when you add the protein, fat and fiber is the carbohydrates percentage!!