Cat food brands are required to give some nutritional details on cat food labels.
They must give a “Guaranteed Analysis” showing the amount of:
Unfortunately, they’re not required to provide you with the carbohydrate levels.
This can make it hard to truly compare two foods to find out which one is lower carb and, therefore, healthier for your cat.
It’s part of the reason we embarked on our huge cat food database project, too. We performed this equation on thousands of cat foods to figure out which ones were low carb.
Luckily, it’s an easy equation.
The Equation To Find Out The Amount of Carbs in Cat Food
100% – Crude Protein% – Crude Fat% – Fiber% – Moisture% – Ash% = Carbs
(If Ash is not listed, assume 8% for dry food and 2 or 3% for wet food)
Here’s an example of a dry cat food we can work through together:
Plugging the numbers from the above cat food label into our formula, we get the following equation:
100% – 43% – 20% – 3.5% – 9% – 8% = 16.5% Carbs
So, this food is roughly 16.5% carbohydrates.
Why This Is Not A Perfect Equation (But Also Why It’s Good Enough)
Unfortunately, the Guaranteed Analysis is a range of minimum and maximum levels.
The actual levels might be a few points higher or lower when the food is actually manufactured, meaning the best way to find out precisely what the macronutrient levels are is by looking at a lab test done of each food.
Sadly, not many brands offer this information.
In some quality cat foods, the number you get from this equation will be a negative number. That just means that there’s probably less fiber or moisture than the maximum Guaranteed Analysis in the actual manufactured food.
Nitrogen-Free Extract (NFE)
The formula above technically gives you the Nitrogen-Free Extract amount, or NFE for short.
NFE basically gives you the carbohydrates, sugars, starches, and a portion of materials classed as hemicellulose.
For our purposes, this just means carbohydrates, so don’t worry too much when you come across a calculation or study online that gives NFE rather than Carbs.
Why The Equation is Good Enough
As noted, you’ll get an imperfect number due to the fact that the Guaranteed Analysis is a range of maximums and minimums, not the actual amount of macronutrients.
However, since all cat foods give measurements in a range, and since this is usually the only data we have to work with, it is as good of a formula as we can hope for.
How To Compare Two Cat Foods, Especially Wet vs. Dry
Using this formula, we can more easily compare two foods by knowing all of the important macronutrients:
However, comparing cat foods is not so simple.
The moisture content in each food varies and makes it hard to compare apples to apples.
To truly compare how good each food is, you need to convert them to a Dry Matter Basis.
This just means you need to remove the moisture from the equation and compare only the dry ingredients left behind.
This way, you can compare wet and dry foods that otherwise look quite different.
For example, is a dry food with a Guaranteed Analysis of 40% protein really better than a wet food with a Guaranteed Analysis of 12% protein?
Since wet food has so much moisture, it’s not a fair comparison. Your cat needs moisture (and should definitely be eating a wet food), but that still doesn’t tell us how much protein she’ll potentially be digesting and absorbing.
To calculate macronutrients into their Dry Matter number, we simply need to remove moisture from the equation.
What we’re left with is the true percentage of protein in a given recipe.
Here’s an example:
Food A: Dry Food, 40% protein (guaranteed analysis), 12% moisture
Food B: Wet food, 12% protein (guaranteed analysis), 80% moisture
We want to know, out of the entire food (100%), what is the percentage of protein out of the digestible portion of the food? (i.e., without water, how much is actually protein?)
Equation: Dry Matter Protein % = (Protein% (Guaranteed Analysis) / (100% – Moisture% (Guaranteed Analysis)) x 100
Food A Dry Matter Protein % = (40 / (100-12)) x 100 = 45.45%
Food B Dry Matter Protein % = (12 / 100-80)) x 100 = 60%
We can see that Food B actually has more protein than Food A.
Doing the same with fat (from the Guaranteed Analysis) and carbs (from our calculations above), we can get a fairly accurate idea of just how much protein, fat, and carbs are in each food, and truly compare the two.