If you are keeping an eye on your carb intake to control your blood sugar levels or weight, you are probably familiar with carb counting. Although fiber does not "cancel out carbs" -- that is, you can't eat a bowl of ice cream and cancel it out by eating a cup of oat bran -- the fiber in a food is considered part of the total carb count. That means, if you're counting the type of carbs that affect your blood sugar, you can subtract the grams of fiber from the total grams of carbohydrate to get a more accurate picture.
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Carbohydrates and Fiber
When you look at a nutrition facts table, you will typically find the suggested serving size at the top of the table and the grams of total carbohydrates per serving lower in the table. Below the total carbs, you will see the fiber content listed in grams. Fiber is accounted for as part of the total carbohydrates found in a food. In other words, it's listed twice -- once in the listing under "fiber" and once as part of the total carbohydrate count, which also includes starches and sugars.
Available Carbs and Your Health
Although starches, sugars and fiber are all part of the total carbohydrates, they are not handled the same way in your body. Sugars and starches elevate your blood sugar levels and can be stored as fat. by contrast, fiber is not absorbed at all and stays in your gastrointestinal tract until it moves through and is eliminated. If you are watching your blood sugar levels or weight, you are typically only concerned with the portion of the carbohydrates that affect your blood sugar levels and weight -- the total carbs, minus the fiber. This calculation is sometimes also referred to as "available" or "net" carbs.
Calculating Available Carbs
You can usually easily calculate net carbs by subtracting the fiber from the total carbs in a serving of food. Other times, it's a bit trickier. For example, certain foods, such as ice cream with no sugar added, use a type of carbs called "sugar alcohol" to provide sweetness. Like fiber, "sugar alcohol" is used differently in the body, and many people don't count these carbs as part of their net carbs.
A medium pear has a total carb content of 27.5 grams and a fiber content of 5.5 grams. All you need to do to obtain the available carbs is subtract the 5.5 g of fiber from the 27.5 g of total carbs, which gives you a total of 22 g of net carbs. The fiber doesn't really "cancel out" the other carbs -- that fiber never affected your blood sugar to begin with, so it's simply a more accurate way of looking at the carbs you consume.