• Isaac J. Wedig MS, CSCS

What are "Net Carbs"?

We've all seen the term "Net Carbs" on protein bars and various diet foods but what does it mean? Is it a marketing scheme or do some carbs really not count as calories?

The term “Net Carbs” is often used on protein bars and other artificially sweetened diet foods, such as diet ice creams, to make you feel like you’re eating a lower number of carbohydrates and calories.

For example, a typical Quest protein bar advertises on the front of the label to contain just 5g of active carbs or 5g of net carbs. However, if you turn the bar over and look at the nutrition label on the back, the total carbohydrate amount listed is 24g.

So how did they end up getting 5g? Isn’t that false advertisement? If you happen to be watching your calorie and carbohydrate intakes this can be a bit confusing. Should you count the protein bar as 5g of carbs or 24g?

Even further, if you do a little math, you’ll find that the macronutrient amounts listed on the nutrition label don’t add up to the calorie amount that is provided. A typical Quest bar lists a calorie content of 170 calories, containing 6g of fat, 24g of carbs, and 20g of protein.

We know that every 1g of carbohydrate yields 4 calories, 1g of protein yields 4 calories, and 1g of fat yields 9 calories. If you do the math, multiplying the total macronutrient amounts listed on the nutrition label by their respective calorie amounts, you get 230 total calories, not 170 calories.

So what the heck are net carbs? How do they calculate them? Should you count the bar as 24g of carbs and 230 calories or 5g of carbs and 170 calories?

Essentially, manufacturers calculate net carbs by taking the total amount of carbohydrates contained in their product and subtracting any carbohydrates that come from either fiber or sugar alcohols.

Net Carbs (g) = Total Carbohydrate (g) - ( Fiber (g) + Sugar Alcohols (g) )

Fiber is a somewhat indigestible carbohydrate that comes from plant sources. There are different kinds of fiber, soluble and insoluble, but we won’t get into the different types and their effects here.

Sugar alcohols are modified alcohol molecules that look like sugar and are often added to lower calorie foods to act as artificial sweeteners. Some common sugar alcohols that you might find in the ingredient list of various diet foods and even tooth pastes include erythritol, sorbitol, mannitol, and xylitol.

While fiber and sugar alcohols typically have little effect on blood sugar and don't yield as many calories as starchy carbohydrates and normal sugars, they still contain calories. The exact amount of energy supplied by them depends on the type of fiber and type of sugar alcohol, however, calculating these numbers is not an easy task or an exact science at this point in time. Typically, sugar alcohols tend to have about half the calories of normal sugar, so about 2 calories per gram. Fiber on the other hand can be a bit more difficult to estimate.

Here’s the take home message and my personal advice:

Count fiber and sugar alcohols as carbohydrates. They still contain calories and certainly aren’t “free foods”. Therefore, if you’re attempting to track calories or are watching your carbohydrate intake, they should be accounted for.

If you consume a Quest bar, I would count it as 24g of carbohydrate and 230 calories. If you go the net carb route, you’re only off by about 19g of carbs and about 80 calories, which isn’t a huge deal, but small inaccuracies can add up over the course of time.

Ultimately, whatever method you use to track foods with fiber and sugar alcohols, be consistent with it! If you track net carbs, then always track net carbs. If you decide to count fiber and sugar alcohols, then always count them. Consistency with how you track it will at least allow you to make manipulations to your diet down the road if you are either losing weight too fast or hit a plateau.


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