These days, just about every drug, supplement, grocery, and department store sells tasty protein snacks claiming that large portions of their carbohydrates don’t “count.”

While one of these bars might list 25 grams of carbohydrate on the nutrition facts panel (which the FDA regulates), the packaging copy (which it doesn’t) offers the friendly reminder that only a few grams of these are “net” or “impact” carbs.

This marketing ploy has been around for a while (Atkins might have started it?), but it’s in the limelight again due to the popularity of the Quest Bar, which is now the subject of a class-action lawsuit (and which I actually like and recommend as a product, despite the misleading marketing).

What’s the real story of the “net carb” and its cousins, “impact” and “active?” Let’s find out.

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The Curious Case of the Disappearing Carbs

We know the sales pitch–eat a delicious, high-protein bars or other type of treats that “cost” only a few of our precious daily carbs–but how does this work, exactly?

What is a net carb and what are the rest? Where do they “disappear” to in our bodies if they aren’t metabolized normally?

Well, these questions lead us to the first problem: these “special” types of carbs have no legal definition and the FDA doesn’t evaluate any claims using them.

What most manufacturers do to calculate them, however, is take the total number of carbohydrates a product contains and subtract fiber and sugar alcohols like sorbitol, maltitol, and xylitol, and list the difference as the “net,” “active,” or “impact” number.

The reason often given for this “adjustment” is that these types of carbohydrates don’t impact blood sugar levels like other types of sugars and thus “don’t count.”

While there’s some truth in this–fiber and certain sugar alcohols like xylitol and erythritol have little effect on blood sugar levels–what most people don’t know is they still contain calories.

That is, the majority of these “invisible” carbohydrates are metabolized by the body and do count to your daily calorie intake.

For example, only insoluble fiber can’t be processed by your body and goes right through you. Soluble fiber turns into a fatty acid in the gut and contains somewhere between 2 and 4 calories per gram (scientists aren’t sure yet).

If you knew how many grams of insoluble fiber were in these products, you could subtract them from the carbs that “count,” but it wouldn’t be more than a few grams at most.

This also applies to your meal planning. If you really wanted to, you could sit down and work out how many grams of insoluble fiber you’re eating every day and subtract that number from your daily carbohydrate intake, but in my opinion it’s not worth the trouble to find out that you can take a few extra bites of food every day.

Like soluble fiber, sugar alcohols contain calories as well, ranging from the 4.3 calories per gram of glycerol (more than sucrose, ironically) to the 0.2 calories per gram of erythritol.

(As an aside, if you want a truly 0-calorie natural sweetener that also comes with some nice health benefits, check out stevia.)

So, all this is why I often hear from people baffled as to why they’re not losing weight despite following their “macros” perfectly, only to find a handful of improperly-accounted-for “net carb” products lurking in their meal plans.

The bottom line is you can eat these foods if you’d like but I recommend you count all the carbs listed on the nutrition facts panel and ignore the marketing buzzwords.

What are your thoughts on net carbs, impact carbs, and the like? Have anything else to share? Let me know in the comments below!