What Are Net Carbs and How to Calculate Them

In calculating net carbs, the formula takes into account how much of an impact fiber has on blood glucose. esolla/Shutterstock

As a way of bolstering the low-carb craze of the past decade, food manufacturers have coined the term "net carbs," which practically guarantees dieters can eat the sweet and salty foods of their dreams without counting their true carbohydrate load.

"This term was invented by food manufacturers during the low-carb craze of the 2000s," says Michelle Dudash, a registered dietitian and author of "Clean Eating for Busy Families." "There is no legal definition for net carbs; therefore it’s not regulated by the FDA on food labels and calculations can vary by each manufacturer."

The only carb information regulated by the FDA is provided on the Nutrition Facts label of foods, which lists total carbohydrates and breaks them down into dietary fiber and sugars.

Dudash says people often go on low-carb diets to lose body fat or to "get cut" before body competitions. "The problem is that going on a low-carb diet typically includes cutting out food groups like grains, fruit and some vegetables, so important nutrients can be overlooked."

The appeal? Calculating a food's net carbs allows you to potentially include more foods in your diet, since the lower the carbs, the better the chance it won’t put you over your carb count for the day. "It’s a numbers game," says Dudash.

How to calculate net carbs

nutrition facts label
Calculations for net carbs start with the nutrition facts label under 'carbohydrates.'. Felix Mizioznikov/Shutterstock

Net carbs is a calculation representing mostly just the starches and sugars in a food after some fiber and sugar alcohol contents have been subtracted. Some types of carbohydrates do not affect blood sugar in the body as much as others, so the thought is that net carbs only account for carbs that affect blood sugar.

This is why food manufacturers include the term "net carbs" on packaged foods marketed as low carb or low sugar — because they are typically designed to appeal to people on low-carb diets.

To calculate net carbs, first subtract all of the insoluble fiber (if listed) from the total carbs and total fiber. If more than 5 grams of total fiber remain, you can also subtract half of the remaining fiber from total carbs. Then look at the sugar alcohols. If there are more than 5 grams of sugar alcohols, subtract half that amount from the total carbohydrates. If erythritol is the only sugar alcohol listed, you may not subtract any sugar alcohols.

“Most manufacturers subtract all of the fiber and sugar alcohols to arrive at net carbs, which isn’t completely accurate,” warns Dudash.

Back when the Atkins diet was really popular, it was all about net carbs, says Leah McGrath, a registered corporate dietitian with Ingles Markets.

Net carbs were originally used for diabetics. For example, when they’re taught carbohydrate counting, dietitians typically teach that if the fiber is 5 grams or greater, subtract that amount from total carbohydrates to get a net carb amount, McGrath explains. "This is mostly useful for Type 1 diabetics, as a higher fiber amount would mean a slower release in carbohydrates."

The formula:

Total carbohydrates per serving minus number of grams of fiber (soluble and insoluble) per serving
minus 1/2 the number of grams of sugar alcohols if 5 or more from total carbohydrates
= net carbs

It's worth noting that Dudash says Atkins oversimplifies the definition of net carbs as total carbs minus dietary fiber and sugar alcohol equals net carbs. She uses the American Diabetes Association rule since there is no legal definition.

Most definitions on food packaging aren’t entirely accurate either since some of the sugar alcohols and fiber are absorbed by the body and can affect blood glucose. However, she says most people don’t need to subtract grams of fiber or sugar alcohols from total carbohydrate when carb counting.

For foods that don't have labels, the calculations aren't so simple. Some people just rely on calculators, like the Atkins Carb Counter.

The value in counting net carbs

"Increasing fiber intake is important for all of us but there is little use in calculating net carbs unless it is for a Type 1 diabetic to plan for insulin release," McGrath says.

Dudash agrees. "People do not need to calculate net carbs. Someone that is following a low-carb diet may want to calculate net carbs since it will allow them to include more carb-containing foods in their diet that they ordinarily wouldn’t be able to."

However, the American Diabetes Association does not recommend using net carbs for meal planning purposes. Instead consumers should use the Nutrition Facts label (which is somewhat regulated by the FDA) and look at the total carbohydrates. If someone is on intensive insulin management therapy and has an advanced knowledge of carb counting, ADA says it is OK to use the calculation above.

For the average person just trying to shed pounds, a much better and more easily tracked approach is to eat mostly fruits and vegetables, a moderate amount of whole grains (cut out refined junk food), a serving of nuts or seeds, and a moderate amount of protein foods.

"I think we have seen a shift from net carbs to glycemic index to now consumers being concerned about sugar," McGrath says.