We like to think we've got a handle on this carb-counting thing. But the truth is, most of us have very little clue -- not least because nutrition labels on packaged products are so darn confusing. One of our beta testers over at the new community recently posted this query:

When I'm counting carbs I often read the "category" of carbs that are in the food I'm eating (i.e. Dietary Fiber, Sugar, Other Carbohydrates, etc.). I have noticed that often they don't quite add up to the Total Carbohydrate amount.

Maybe this is a stupid question with an obvious answer but:

Does anyone know what these "mystery carbs" are or where they come from?

Not a stupid question at all. I couldn't answer it off-hand. Why are we consuming more carbs than appears necessary or possible based on the corresponding food data? For some insight, I turned to local San Francisco nutrition expert Norae Ferrara. Of course, nothing is simple with diabetes. The answer was much more than I bargained for. Here's what this food whiz had to say:

Label reading can be tricky because the original purpose which is to provide accurate, useful, information is also clouded by marketing strategies of most companies who may add more information than is required, or practice "rounding" of values to emphasize or de-emphasize certain components.

To further explain:

Definition of Carbohydrates

Carbohydrates are made up of: 1) Complex Carbohydrates, 2) Simple sugars (or sugar), and 3) Dietary fiber (sometimes separated into soluble and insoluble on the label)

Required Labeling of Carbohydrates in the US:

United States Federal Law requires that companies state on the nutrition facts label the total grams of carbohydrates, dietary fiber, and sugars. This makes listing the content of complex carbohydrates as optional, which in most cases, will make up for the difference between total carbohydrate, and the sum of dietary fiber and sugars.

A truly complete label for a breakfast cereal might look like this (remember, each time a component is listed as a subgroup--underneath and indented to the right--it means that it is included in the total listed above):

Total Carbohydrate 24g

Dietary Fiber 3g

Soluble Fiber 1g

Insoluble Fiber 2g

Sugars 10g

Other Carbohydrate 11g

While the more common food label will list only what is required, for example the same product might also be listed as:

Total Carbohydrate 24g

Dietary Fiber 3g

Sugars 10g

Rounding:Companies may choose to round up or down to the nearest .5g. They may choose to round .3g fiber up to .5g, or just call it "less than 1g", when it is a desired component, or they may choose to round .3g sugar to 0g, for example, when the component is not highly desirable.

That sounds pretty sneaky to me. Might be OK for enticing dieters to eat their products, but a veritable nightmare for anyone attempting to dose insulin based on that information. No wonder I manage to make frequent "mistakes" even when I'm eating neatly labeled foods. I know what you're thinking: don't trust the packaging, learn to estimate carbs yourself -- within a fraction of .5g. Correct. Great strategy. But it seems like that could take a lifetime, and a lot patience that I do not possess. *Sigh*

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This content is created for Diabetes Mine, a consumer health blog focused on the diabetes community. The content is not medically reviewed and doesn't adhere to Healthline's editorial guidelines. For more information about Healthline's partnership with Diabetes Mine, please click here.