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What are soluble fiber, insoluble fiber and impact carbs?

By Shereen Jegtvig, About.com

Updated February 13, 2008

About.com Health's Disease and Condition content is reviewed by our Medical Review Board

Fruits and vegetables are sources of both soluble and insoluble fiber.

Fruits and vegetables are sources of both soluble and insoluble fiber.

Photo © Richard Styles
Question: What are soluble fiber, insoluble fiber and impact carbs?
I have read about the importance of fiber and have discovered the classification of "Soluble" and "Insoluble" fiber. What is the difference and should there be an attempt to obtain both types into our diets? If so, how much?

I've recently noticed on health bars the introduction of the term, "Impact Carbs" and "Sugar Alcohol." Are these marketing ploys which give a false sense of security for those of us who are reducing our complex and simple carb intake?

C Anderson - About.com User

Answer: Fiber is the part of plants that you can’t digest, so it passes through the digestive system into the colon. Fruits, vegetables, grains, legumes are all high fiber foods. There are two types of fiber, insoluble and soluble fiber.

Insoluble fiber is so named because it does not dissolve in water. Insoluble fiber increases stool bulk and keeps things moving through the colon. This type of fiber is important to keep your bowel movements regular. Insoluble fiber is found in whole grains, brans, nuts and vegetables.

Soluble fiber is so named because it will dissolve in water and then it becomes somewhat gelatinous. Soluble fiber will help to keep your cholesterol and blood sugar levels healthy. Soluble fiber is found in oats, barley, legumes, fruits and psyllium.

Men should consume at least 30 to 38 grams of fiber each day and women should consume at least 20 to 25 grams of fiber each day. Of that fiber consumption, at least seven grams should be soluble fiber.

Impact carbs are carbohydrates that will cause a rise in insulin, such as sugar, corn syrup and glucose. Most of the time this is equal to the total carbohydrate minus the amount of fiber in a food product. Alcohol sugars are substances that are used to sweeten low-carb foods because they do not cause a rise in insulin levels.

Alcohol sugars have fewer calories than regular sugar, but you need to read food labels to know just how many calories are in the food product you are eating. Alcohol sugars are useful for diabetics and people on low carb diets when they are consumed in moderate amounts. Excessive consumption of foods with sugar alcohols will still cause blood sugar to rise, add calories and cause gas and bloating in many people.

Sources:

Mayo Clinic."Dietary fiber: An essential part of a healthy diet." December 2005.

Yale-New Haven Hospital. "Eat any sugar alcohol lately?" Updated March 2005.

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