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Ask The RD: Are all types of fiber created equal?

Question: I know that it is best to avoid overly processed foods as much as possible. But isn’t
the fiber found in fortified foods such as breakfast cereals as good for you as the fiber found in naturally occurring foods? In other words, aren’t all types of fiber created equal?

Answer: Actually no. But I am happy to hear you make the distinction between the fiber found in naturally occurring foods and the fiber added to processed foods. The fact that many consumers believe that a high-fiber product, regardless of its source, is a healthful option is not surprising. But all fibers are not identical and as a result do not provide the same health benefits


The fiber that occurs naturally in foods is called intact fiber. This fiber can be categorized as either soluble fiber (found in grains, nuts, fruit skins and vegetables, it tends to speed the transit time of food in the intestines) or insoluble fiber (found in beans, oats, and some fruits and vegetables, it tends to slow the rate of digestion and absorption). Isolated fiber is either chemically synthesized or isolated and extracted from certain plant foods and then added to processed foods to boost fiber intake. These types of fiber appear on ingredient lists under names such
as “resistant starch,” “polydextrose,” “indigestible dextrin” and “inulin,” among others.


Intact fiber has a wealth of health benefits, ranging from aiding digestion to reducing the incidence of obesity. But it is fiber’s long-term benefit—being a key element in the prevention of certain cancers, cardiovascular disease and diabetes—that is most impressive. (Epidemiological studies show that populations with high fiber intake have a lower incidence of chronic disease.)


Essentially, the synergistic effect of fiber and other biologically active components found in whole foods are what have been credited with offering protection against chronic disease. This doesn’t mean your fiber-fortified breakfast cereal isn’t good for you; it’s just not as good as the naturally occurring fiber found in old-fashioned oatmeal.

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