Carbohydrates aren't just one simple nutrient. So that's why the number of total carbohydrates you see on a food's nutrition facts label includes the sugar, fiber, starch as well as sugar alcohols.
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If you're trying to reduce your sugar intake, knowing what percentage of your carbohydrate intake is sugar allows you to track how you're doing and adjust your eating habits if necessary. The nutrition facts label on a product has all the numbers you need to do some simple math to get your answer.
Carbs to Sugar Conversion
Our bodies break down sugars and starch into a simple sugar called glucose, which we use for energy. One gram of sugar on a nutrition label equals one gram of carbohydrate.
Within 15 minutes of eating carbs, your body will begin to convert them into glucose, causing your blood sugar to begin its rise. About 90 minutes after a meal, most of the carbs will have broken down, and your blood sugar will be at its highest point, per the University of Maine Extension.
Calculating Sugar Totals
1. Look at the Nutrition Facts Label
Read the nutrition label and find the line for the "Total Carbohydrates" and the line for "Total Sugars." The total carbohydrates will have both a percentage and a number in grams. Find the grams of total carbohydrates and the grams for total sugars.
Let's use this example: A label lists 28 grams of total carbohydrates and 6 grams of total sugars.
2. Divide Total Sugars by Total Carbs
Divide the number of grams of total sugars by the number of grams from the total carbohydrates line.
For this sample label, you would divide 6 by 28 to get 0.214.
3. Change to Percentage
Move the decimal point two spaces to the right or multiply by 100, if you prefer using an equation, to get you the percent form of the number.
Using the 0.214 from Step 2, you'll end up with 21.4 percent of the total carbohydrates coming from sugar.
Sugar Alcohols and Fiber
Sugar alcohols and fiber are also listed on nutrition labels, but these nutrients are not digested the same or used by the body in the same way as sugars and starches.
Sugar alcohols sweeten foods without adding calories because they can't be fully digested, according to the Cleveland Clinic. Common sugar alcohols include xylitol, sorbitol, erythritol and mannitol.
Fiber can be in the form of soluble fiber or insoluble fiber and is found in foods like fruits, vegetables, whole grains and legumes. The small intestine can't break down and absorb fiber the same way it does sugars and starches, so fiber doesn't affect blood sugar levels in the same way, per the Centers for Disease Control and Prevention (CDC).
Calculating Net Carbs
To calculate the total carbohydrates that will affect your blood sugar — which are also called net carbs — just subtract the fiber and sugar alcohols from the total carbohydrates.
So if a food has 30 grams of total carbohydrates, 5 grams of fiber and 3 grams of sugar alcohols, then the number of carbohydrates affecting your blood sugar would be 30 grams (total carbohydrate) - 5 grams (fiber) - 3 grams (sugar alcohols) = 22 grams net carbohydrates.
Remember that all sugars are counted in the Total Sugars line on the nutrition label — that includes natural sugars. Added sugars can be found in a separate line under the total carbohydrates.
- United States Department of Agriculture: "Dietary Guidelines for Americans 2020-2025"
- Cleveland Clinic: "What You Should Know About Sugar Alcohols"
- CDC: "Fiber: The Carb that Helps You Manage Diabetes"
- University of Maine Extension: "Diabetes, Carbohydrates and You: Paying Attention to Carbohydrate"