Personally I think that net carbs is a concept of little value. However, if you are subtracting the grams of fiber from total carbohydrates in a food in order to estimate the effect of that food on your blood sugar, be advised that recent research has changed how to do this.

The old method of determining net carbs was to subtract the amount of fiber from the total carbs if the amount of fiber in the food was greater than five grams (This is another thing that makes no sense to me. Why would you only subtract the fiber if it is greater than five grams?).

At any rate, if you had a food with 20 carbs and there were five grams of fiber in this food, then you would subtract 5 from 20 and the net effect, so to speak, would be 15 grams of carbs. The reason that you subtract the fiber is because the body does not fully absorb it. Now researchers are saying that the body is able to use about half the fiber through a process called anaerobic fermentation.

So now when you make your calculation, only subtract ½ the fiber that is listed. In our previous example that would leave a net effect of about 17.5 grams of carbohydrates.

Will this make any difference in calculating the number of carbs you consume per day? Not much, but every little bit helps. Whatever the food is and its fiber content, personal testing of how it affects YOU, is the most important thing and something that you should do on a regular basis for any foods that you eat.