Total carbohydrates are determined by subtracting the grams of protein, fat, water, and ash from the total weight of the food. The Food and Drug Administration (FDA) requires that the total carbohydrate count include the full grams from both sugar alcohols and fiber. However, these carbohydrate sources have a much lower impact on your blood glucose levels than regular carbohydrates because they are only partially converted (if at all) to glucose by your body. Sugar alcohols are not completely digested by the body (nor is fiber), but they do contribute some calories. A gram of regular carbohydrate (from foods like grains, fruits, vegetables, dairy, sweets, etc.) yields 4 calories. However, sugar alcohols (scientific name "polyols") are a group of low-digestible carbohydrates that provide a range of calories per gram--from 0.2 to 3 calories/gram. They aren't completely calorie-free, but they provide fewer calories per gram than regular carbohydrates (4 calories/gram).
The words "net carbs" do not have a legal definition, and neither the FDA nor the American Diabetes Association uses the term. The idea behind net carbs is that food manufacturers subtract certain incompletely-digested carbohydrates--including sugar alcohols, fiber and glycerine--from the total carbohydrates (grams) because not all of the calories from those carbohydrates are completely absorbed by the body. For example, the term "net carbs" is often used on packages of foods that contain a large amount of dietary fiber or sugar alcohols. Sugar alcohols are used to sweeten a lot of sugar-free/no-sugar-added candies, gums, ice-cream, baked goods, and chocolate. However, subtracting all of the carbohydrate grams is inaccurate because a portion of them are absorbed.
For diabetics, if the food contains greater than 5 grams of sugar alcohols, subtract half of those from the total carbohydrates and use that number--which gives you net carbs--to adjust your insulin dosage or meal plan accordingly. If the only sugar alcohol on the ingredient list is erythritrol, subtract all of the grams of sugar alcohols.
For those worried about counting total grams of carbohydrate and/or calories, such as those trying to lose weight or maintain a healthy weight, don't concern yourself with calculating net carbs. Bottom line: Unless you have diabetes, calculating net carbs won't be useful for you. Chock all this label-lingo confusion up to food companies looking to make money off another fad diet.
Kari Hartel, RD, LD is a Registered Dietitian and freelance writer based out of St. Louis, MO. Kari is passionate about nutrition education and the prevention of chronic disease through a healthy diet and active lifestyle. Kari holds a Bachelor of Science in Dietetics from Southeast Missouri State University and is committed to helping people lead healthy lives. She completed a yearlong dietetic internship at OSF St. Francis Medical Center in Peoria, IL, where she worked with a multitude of clients and patients with complicated diagnoses. She planned, marketed, and implemented nutrition education programs and cooking demonstrations for the general public as well as for special populations, including patients with cancer, heart disease, diabetes, Alzheimer's disease, obesity, and school-aged children. Contact Kari at KariHartelRD@gmail.com.