the scientific study of pet nutrition by veterinary nutrition specialists and experts.
Carb Confusion: Part 2 – Measuring and Comparing Carbohydrate in Pet Foods
In part 1 of this topic, we defined the term carbohydrate and discussed whether pets need carbohydrates and reasons why carbohydrates are included in pet foods. For the majority of pets, the actual amount of carbohydrate in the diet doesn’t matter. But there may be some situations where this information could be useful. That leads us to what is probably the most frustrating aspect of carbohydrate in pet food – trying to figure out how much is actually in a specific food!
You may have noticed that while protein, fat, fiber, and moisture are always provided on the label of a pet food as part of the Guaranteed Analysis, carbohydrate is not listed. In very rare cases, you might see maximums for starch and dietary sugars, two types of carbohydrates, but we’re going to focus on the average pet food, which will not have this information.
The standard way to determine the amount of carbohydrate in a pet food is to measure the moisture, crude fiber, protein, fat, and ash (mineral) and then to assume that whatever is left is carbohydrate. The technical term for whatever is left after subtracting out all these other nutrient types is “nitrogen free extract” or “NFE”. NFE includes not only digestible carbohydrate, but also soluble fiber (which is missed in the crude fiber test), vitamins, and any errors or variation in the tests for the other nutrients. So, while a pet food manufacturer will tell you the NFE when you ask for “carbohydrates”, this number may overestimate the actual amount, especially in diets that are high in soluble fiber.
The NFE also doesn’t provide any information on how the body will handle the carbohydrate, or what type it is. Let’s use the example of a medium-sized apple. An apple has around 22 grams of carbohydrate (NFE) in it. This is the same amount of carbohydrate as in 5 & ¼ teaspoons of table sugar. However, table sugar and apples are not at all equivalent in terms of their nutritional properties – apples bring in fiber and a number of essential nutrients and healthy compounds, whereas sugar is just “empty” calories. Similarly, if we look at two different dry pet diets, and one has 30% NFE and the other has 40% NFE, that information alone doesn’t give us any information on how those diets will be metabolized by the pet because this will vary by the type and source of carbohydrate. Percentages are also not the best way to compare foods, regardless of the nutrient you are considering (check out our post on comparing foods).
The important thing to keep in mind is that in most cases, the amount of carbohydrate in a diet doesn’t really matter, so the lack of accuracy and specificity that is inherent with NFE is not important. However, if a pet has a health condition (e.g. a diabetic cat) that may benefit from a certain amount or type of carbohydrate, then it will be important to investigate diet options in much more detail. It is also wise to avoid getting hung up on small differences in the amounts of carbohydrates between diets as these differences may not be real or make any difference to your pet.
Rather than being measured directly, carbohydrates are determined “by difference” in pet food – by assuming that everything that isn’t fat, crude fiber, protein, moisture or mineral is carbohydrate. This measurement of “carbohydrate” is usually called the “NFE”. Unfortunately, the assumption that NFE equals digestible carbohydrate is not always accurate. Moreover, this value does not take into account the source of the nutrient, nor how it is metabolized. Thankfully, for most pets, the type and amount of carbohydrates usually doesn’t make any difference so precise measurements are unnecessary.
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