Ask Dr. Hirsch: Net Carbs

Q. I take insulin and use carb counting in the management of my diabetes. Recently I have noticed more food packaging claiming "NET CARB" values.  These do not always reflect the carb values that are on the smaller nutritional charts on the side.  How do these affect my concerns and my calculations? 

A.  Many people are confused by the terms net carbohydrate or impact carbohydrate which appear on some food labels.  Food manufacturers have identified this new category of carbohydrate, but there is no legal definition for this term. 

The only carbohydrate information regulated by the FDA is provided on the “nutrition facts” label, which lists total carbohydrates and then breaks carbohydrate down into dietary fiber, sugar and sugar alcohols. 

The concept of net carbohydrates is based on the idea that certain carbohydrates contribute to increased blood sugar levels while others do not. 

• Fiber - a non-digestible type of carbohydrate - and sugar alcohols such as sorbitol, mannitol and xylitol are not counted in net carbohydrates.
  
  
• Net carbohydrates are calculated by taking the total number of carbohydrates in a food item and subtracting fiber and sugar alcohols. While fiber does not affect blood sugar or supply calories, the same is not true of sugar alcohols.  Sugar alcohols do not raise blood sugar as much as the same amount of other carbohydrates, but they still need to be counted by someone with diabetes.
  
  
• Ideally, if you have diabetes and want to correctly account for the amount of carbohydrate which will have an effect on blood sugar, you should first check the nutrition facts label for total carbohydrate.
  
  
• Second, check the grams of fiber.  If there are more than five grams of fiber per serving subtract this from total carbohydrate.
  
  
• Finally, subtract half of the amount of sugar alcohols grams from total carbohydrate. For example if the total amount of carbohydrate in a serving of sugar free ice cream is 15 grams and there are 6 grams of sugar alcohol, then one serving of this ice cream is 12 grams of carbohydrate (15-3=12). 

Some other things to keep in mind about sugar alcohols is that they contribute ½ the amount of calories and can cause a laxative side effect (bloating, cramping or diarrhea) in some people.

If you have a question about diabetes care that might be of interest to the readers of this column, please e-mail it to askdrhirsch@bd.com. Dr. Hirsch cannot comment on individual medical cases.

Laurence J. Hirsch, MD Worldwide Vice President of Medical Affairs, BD Diabetes Care Dr Hirsch graduated from the University of Rochester and then attended Harvard Medical School.  He is board-certified in Internal Medicine and in Endocrinology/Metabolism. Prior to joining BD, he was Assistant Professor of Medicine at Northwestern University, and spent more than 17 years in various roles in clinical drug development at Merck.