June 2012 Issue
Calculating a Dog Food Diets Protein, Fat, Carbs, and Fiber
It is not easy to figure out how much fat and other nutrients are really in the food you feed, whether it’s kibble, canned food, or a home-prepared raw or cooked diet. Here are some tips that can help.
Methods of Measurement
There are three different ways of measuring amounts of protein, fat, carbohydrates, and fiber in foods:
-Percentage of dry matter
-Percentage of calories (does not apply to fiber)
-Grams per 1,000 calories
Dry matter percentages are easiest to use for commercial foods. Grams per 1,000 calories or percentage of calories are simpler ways to measure nutrients in a homemade diet.
Pet food labels give you some, but not all, of the information you need in order to really know the nutritional composition of your dog’s diet.
-The percentages of protein, fat, and fiber shown on dog food labels are guaranteed minimums and maximums, NOT actual amounts. The real amount of fat in particular may be much higher than what is shown on the label of some canned and raw diets. If your dog needs a low-fat diet, look for products that are lower in calories than similar foods.
For more accurate information, contact the company that makes the food you’re interested in and ask them for a nutritional analysis showing the actual amount of protein, fat, fiber, ash, and moisture, as well as the number of calories in the food. Editor’s note: Some pet food makers (particularly small companies) may not have a complete nutritional analysis of their products. In our opinion, this reflects a lack of adequate research and investment in the product. When feeding a special needs dog, we’d look to a company who has this current information on hand.
-The percentage of carbohydrates is not included on most labels or nutritional analyses. To calculate the percentage of carbohydrates in a commercial diet, subtract the percentages of protein, fat, moisture, crude fiber (an indigestible part of carbohydrates), and ash from 100. This percentage may be shown as “nitgrogen-free extract (NFE)” on a nutritional analysis.
-Total dietary fiber is likely much higher than the crude fiber shown on the label. If dietary (soluble plus insoluble) fiber is not shown on a complete nutritional analysis, there is no way to calculate it.
When feeding a home-prepared diet comprised of fresh food ingredients, it can be a bit more challenging to calculate some of the nutrient values that you’d like to know when feeding a diabetic dog.
-To calculate the caloric content of the food, look up the ingredients or enter a recipe on NutritionData.com. The number of calories from protein, fat, and carbohydrates, along with the total calories, are given in the “calorie information” section, and the calorie percentages are shown in the “caloric ratio pyramid.”
-To calculate the grams of protein, fat, etc., per 1,000 calories, divide grams of any nutrient by total number of calories, then multiply by 1,000 to get grams per 1,000 kcal. For example, raw skinless chicken breast contains 6.5 grams of protein, 0.3 grams of fat, and 30.8 calories per ounce:
6.5 ÷ 30.8 x 1,000 = 211 grams of protein per 1,000 kcal
0.3 ÷ 30.8 x 1,000 = 9.7 grams of fat per 1,000 kcal (GFK)
=“as fed” versus “dry matter”
The percentages of protein, fat, etc., shown on a pet food label are expressed “as fed” – meaning, as the food is delivered in its package. Some percentage of the food is comprised of moisture (water), which of course contains no protein, fat, fiber, or other nutrients. Kibble generally contains about 10 percent moisture; wet foods (canned, frozen, or fresh) contain as much as 80 percent or more moisture.
So, think about it: When a label says that a food contains
(for example) 4 percent fat, in order to really understand how much fat you are about to feed your dog, you also have to know how much moisture is in the food. What you really want to know is how much fat (in this example) is in the food part of the food – the “dry matter.” Any serious discussion of nutrition, or comparison of dry and wet diets, then, requires the conversion of the nutrient values from “as fed” to “dry matter.” Don’t worry; it sounds technical, but it’s easy to do.
-To calculate dry matter (DM) percentages, first determine the amount of dry matter by subtracting the percentage of moisture from 100. Then divide the “as fed” percentage by the amount of dry matter to get the dry matter percentage. For example, if a canned food has 75 percent moisture and 4 percent fat:
100 - 75 = 25 percent dry matter
4 ÷ 25 = 16 percent fat on a dry matter basis
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