Info Calculating % Calories from Carbohydrates

A priority in managing feline diabetes is feeding a low carb, preferably canned or raw, diet. Information provided by commercial pet food companies can be confusing as to the % of calories from carbs, protein, and fat that are in a specific food.

Dr. Lisa has provided a wealth of information on the nutrient analysis of foods in her Cat Food--Nutritional Composition charts; however, how we do we determine this information for a food not listed on the charts or where the commercial pet food company has changed the formula of the food?

First, I'll explain the how to use information provided by commercial food companies and some definitions. Second, I’ll show you how to do the necessary calculations.

I. How to Use Information Provided by the Commercial Pet Food Company

Many websites and the cat food can (or bag) use the term “guaranteed analysis” (GA) with maximums and minimums. While the Scheyder calculator was developed by a non-FDMB layperson to try and convert GA values into values one would get if you had the as-fed or dry matter basis (DMB) values, I’ve found it to be inaccurate. With a little effort, more accurate calculations are attainable.

Pet food regulation require pet foods to list the GA which is shown as the guaranteed maximum or minimum for crude protein, crude fat, crude fiber, and moisture. For example, the GA for crude protein for Merrick’s Purrfect Bistro Cowboy Cookout is minimum 9%. That is all it is required to have but it could actually have much higher. Not all pet foods equate the GA to as-feds; a good explanation is provided in this detailed but enlightening article.

Commercial pet foods are also required to have a nutrient analysis conducted of the food based on testing of the food once it is made. They are not required to post it on their website or even provide it to a consumer who asks for it. If a commercial pet food company is not willing to share this information with a consumer, the consumer should think twice about whether they want to feed this specific food.

In most cases, the commercial pet food company will not provide this information on their website and does not provide it on the can/bag. Most will provide it if the consumer calls and asks for the “typical nutrient analysis”, not GA. However, there are some that will post it on their website specifically as “as-fed” or “DMB” separate from GA and some, like Merrick, will actually list their “as-fed” values as GA values, which is legal for them to do. It’s important to closely read the website to see how a specific company is listing their information.

Usually, for canned foods, the nutrient analysis is reported as "as-fed" or "as-served" meaning as it comes out of the can. Conversely, due to the lack of moisture in dry foods, the nutrient analysis for dry food is reported on a DMB.

Obviously, to compare the % of calories from carbs in a specific canned food with % of calories from carbs in a specific dry food, both foods must be considered from a DMB. Likewise, to compare two canned foods, they must be evaluated using either “as-fed” or “DMB” values (use the same basis for both foods). Confusion can further arise if a company provides values for a macronutrient both as “as-fed” and DMB without explaining that a conversion is necessary.

Using an example from information recently provided by Merrick, Purrfect Bistro Cowboy Cookout is 3.9% carbs on an as-fed basis and 21% carbs on a DMB. One might wonder how the two numbers can differ so drastically and which to use in determining whether this food is acceptable to feed to a diabetic kitty.

To compare them, first, take the moisture stated in the “as-fed” out by subtracting the % moisture from 100. In this case, the as-fed value for moisture in this canned food was 81%. The dry portion is calculated as:
100 - 81 = 19

Second, take each as-fed value provided and divide by 19 (the dry portion).
Protein: 9/19 = 0.47 or 47% on a DMB
Fat: 3/19 = 0.16 or 16% on a DMB
Carbs: 3.9/19 = 0.21 or 21% on a DMB

With this conversion, we can now see that, for this food, 3.9% carbs on an as-fed basis is the same as 21% carbs on a DMB.

However, the above information still does not actually tell us the % of calories from carbohydrates which is the crucial number we need.

II. Calculating the % of calories from each macronutrient both for as-fed and DMB.

There are two ways to calculate the % calories of a macronutrient (fat, protein, carbs). Both the as-feds or the DMB can be used but if comparing two foods, be sure to use the same basis (e.g. either as-feds for both or DMB for both).

For this example, I’m using Wellness Core Chicken, Turkey, and Chicken Liver canned food as the company includes both as-fed and DMB values on their website which affords the opportunity to see how the same % calories from a macronutrient is determined using either method.

Calculating from As-Fed Values

Step One: Protein, Fat, Carbs, Moisture, Ash and Fiber should equal 100.

Moisture = 72.27
Protein = 13.18
Fat = 8.54
Ash = 2.89
Fiber = 0.41
TOTAL = 97.29

Step Two: Because most companies won’t list carbs, estimate it by subtracting the other ingredients listed above from 100. Wellness provides the % carbs, but for this example, we will estimate it:
100 - 97.29 = 2.71

Step Three: Determine the calories from each macronutrient.

For pet food, there are 3.5 calories per gram of protein and also 3.5 calories per gram of carbs. There are 8.5 calories per gram of fat. Using this info, we can calculate how many total calories there are from protein, carbs, and fat in this food.

Protein: 13.18 x 3.5 = 46.1 calories
Fat: 8.54 x 8.5 = 72.6 calories
Carbs: 2.71 x 3.5 = 9.5 calories

Total the calories from above: 46.1 + 72.6 + 9.5 = 128.2 calories.

Step Four: Determine the % of each from total calories:

Protein: 46.1/128.2 = 36%
Fat: 72.6/128.2 = 57%
Carbs: 9.5/128.2 = 7%

This tells us that Wellness Core Chicken, Turkey, and Chicken Liver is a low carb food at 7% calories from carbohydrates.

This is almost identical to Dr.Lisa’s food chart (pg 56). The differences are likely because the food companies periodically retest the food and update the nutritional info based on the most recent testing.

Calculating from DMB

Step One: Protein, Fat, Carbs, Ash, and Fiber should equal 100.

Protein = 47.53
Fat = 30.8
Ash = 10.42
Fiber = 1.48
TOTAL = 90.23

Step Two: Because most companies won’t list carbs, estimate it by subtracting the other ingredients listed above from 100. Wellness provides the % carbs, but for this example, we will estimate it:
100 - 90.23 = 9.77

Step Three: Determine the calories from each macronutrient.

For pet food, there are 3.5 calories per gram of protein and also 3.5 calories per gram of carbs. There are 8.5 calories per gram of fat. Using this info, we can calculate how many total calories there are from protein, carbs, and fat in this food.

Protein: 47.53 x 3.5 = 166.4 calories
Fat: 30.8 x 8.5 = 261.8 calories
Carbs: 9.77 x 3.5 = 34.2 calories

Total the calories from above: 166.4 + 261.8 + 34.2 = 462.4 calories.

Step Four: Determine the % of each from total calories:

Protein: 166.4/462.4 = 36%
Fat: 261.8/462.4 = 57%
Carbs: 34.2/462.4 = 7%

As can be seen, we were able to calculate the % calories from carbs using either the as-fed or DMB values and obtain the same number.

 

Thank you, Marje!

 

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