If you routinely read food labels, then you’ve probably come across the term “net carbs.” The Food and Drug Administration (FDA), the agency responsible for what items are included on food labels, only recognizes total carbohydrate, dietary fiber, and sugars. The concept of net carbs was first introduced in 2002 in the book Dr. Atkins’ New Diet Revolution as a way to minimize the impact of carbohydrate on blood sugar levels and insulin production. Although the FDA allows “net carbs” to appear on food packages, it doesn’t have a legal definition for this term.

What Are Net Carbs?

The simple definition of net carbs is total carbohydrate. In this usage, fiber and sugar alcohols are also net carbs. This is based on the principle that not all forms of carbohydrate affect the body in the same way.

“Carbohydrate” is the umbrella term for starch and sugar. It can be further divided into simple and complex carbs based on the chemical structure of the carbohydrate in the food. Foods that contain more simple carbohydrates — think white bread and white rice as well as foods that are high in sugar — are digested quickly and cause a rapid increase in blood sugar after eating. Highly refined snack foods like potato chips and pretzels also fall into this “simple carbohydrate” category.

Foods higher in complex carbohydrate such as whole grains, fruit, vegetables and legumes are all digested more slowly, which in turn leads to a smaller impact on blood sugar levels. Fiber in foods is only partially digested, so fiber also causes a smaller impact on blood sugar. Sugar alcohols, a.k.a. polyols are also incompletely digested and have a much lower blood sugar impact than simple sugars. Some foods (cherries, peaches, plums, mushrooms, avocado for example) naturally contain polyols, and polyols are also added to foods to replace sugar to provide the sweet taste we love with fewer calories. 

However there are nuances to fiber and sugar alcohols that make a simple net carb calculation inaccurate. Even though they are incompletely digested, sugar alcohols and fiber contain carbohydrate, which means they have some impact on blood sugar. Also, incomplete digestion can lead to side effects such as gas, bloating, and diarrhea. While eating more fiber is a healthy strategy, sometimes food manufacturers add inexpensive types of fiber to make their products look healthier. The recommendation to consume 25-35 grams of fiber per day is based on fiber that naturally occurs in foods like vegetables, whole grains, legumes, and fruits – not on isolated forms of fiber added to highly processed foods.

Reasons to use net carb information:

• Net carbs are a quick and simple way to choose foods with less absorbable carbohydrate to help manage blood sugar and weight.

• If you’re following a very low-carbohydrate eating plan such as keto or Atkins, using net carbs will help you find foods that meet your carbohydrate goals.

Reasons to not use net carb information:

• Foods that list net carbs are typically highly processed, and limiting processed foods is one key health strategy.

• Some types of sugar alcohols can lead to diarrhea, gas, and bloating.

• If you’re following a FODMAPS diet, most sugar alcohols are off-limits due to negative gastro-intestinal side effects.

• While regularly consuming foods that naturally contain fiber is an important health strategy, adding fiber to processed foods hasn’t been shown to improve health.

• Just because a food is low in net carbs doesn’t mean that it provides the nutrients our body needs for good health.

References:

1. Food Consulting Company. Food Labelers Beware:  Carbohydrate Labeling is Tricky. https://www.foodlabels.com/press-release-carbohydrate-claims published 3-1-2004; accessed 12-20-22

2. WebMD. When a Carb’s Not A Carb: The Net Carb Debate. https://www.webmd.com/women/features/net-carb-debate  accessed 12-20-22

3. Atkins. What are Net Carbs? https://www.atkins.com/how-it-works/library/articles/what-are-net-carbs  accessed 12-20-22

4. Monash University. What are Polyols? https://www.monashfodmap.com/blog/what-are-polyols/ posted 4-17-16; accessed 12-20-22

5. U.S. Food and Drug Administration. Questions and Answers on Dietary Fiber. https://www.fda.gov/food/food-labeling-nutrition/questions-and-answers-dietary-fiber#define_dietary_fiber  Updated 12-17-21; Accessed 12-20-22

6. Calorie Control Council. Polyols. https://polyols.org/about-polyols/  Accessed 12-20-22