Resistant Starch

Dietary Fiber FAQ


Dietary fiber is the part of plant foods that resists digestion.  Folk medicine tells us that “roughage” is important, but most of us are still confused about why something that isn’t even digested is so critical to human health.  This FAQ explains the types of fiber, its benefits and what to eat to get enough fiber. Feel free to share it with your patients and your loved ones.


Q       What’s the big deal about fiber?  Why do we need it?

A       Fiber promotes healthy intestinal function, influences weight control and is a critical part of a balanced diet in many ways.


Q       I’m not constipated; my bowels work fine.  So I don’t need fiber, right?

A       There’s more to intestinal and digestive-tract health than avoiding constipation.  Recent studies have found that certain types of fiber –


·         slow the absorption of glucose and reduces insulin requirements1

·         remove bile acids from the intestines and blocks synthesis of cholesterol, lowering cholesterol levels 2

·         reduce the likelihood of colorectal cancer3

·         discourage overeating, by filling the stomach4


In fact, your intestines are a major component of your immune system. Adequately maintained and nourished, your intestines can help protect you against scores of pathogens and diseases.  When you consume dietary fiber, you accomplish this goal. It is important to eat a variety of fibers to obtain the optimal benefits of each type.


Q       I’ve heard there are different kinds of fiber.  Which is better?

A       It’s long been thought that there were only two kinds of fiber – soluble and insoluble.  Now there is a third kind – resistant starch.  All three kinds of fiber are essential to health, so we can’t say that one is “better” than another.

·        Soluble Fiber like pectins, gums, mucillages, and some hemicellulose): These help lower blood cholesterol levels and controls blood sugar.

·        Insoluble Fiber such as cellulose, lignan and hemicellulose. These provide bulking and helps keep us “regular.” 

·        Resistant Starch – the ‘trendiest’ form of dietary fiber – is insoluble but is fermented like soluble fiber, giving us some of the health benefits of both – plus some unique advantages of its own.


Q       What should I eat to get all three kinds of fiber?

A       Fiber comes only from plant foods; it isn’t found in meats, fish or dairy products. 


In general, soluble fiber is found in oatmeal, barley and rye; beans, peas and lentils; fresh and dried fruits, and most vegetables. 


Insoluble fiber is found in the skins and seeds of fruits and vegetables; in wheat bran; and in whole grains – including popcorn. 


Resistant starch is found in whole grains, seeds, legumes, under-ripe fruit, and is especially prevalent in cooked starches that have been cooled – such as pasta salad, potato salad and sushi rice.  It can also be found in packaged foods that contain selected new ingredients designed to provide resistant starch.


Many foods contain all three kinds of fiber, so your best plan is to eat the widest variety possible of fruits, vegetables and grains. 


Q     How much fiber should I eat every day?

A       In 2002 the US government5 set the daily recommended intake (DRI) for fiber at 38g per day for men under age 50, and 30g per day for older men.  For women, the DRI is 25g per day under age 50 and 21g per day over 50. 


Men and women, young and old require about the same proportion of fiber in their diets; the actual fiber amounts vary only because these different groups eat different levels of calories.


Q       That doesn’t sound like much.  I probably get that much already.

A       Probably not.  The average American gets only about 13 grams (women) to 17 grams (men) of fiber per day, much less than recommended.  Europeans on average eat more fiber, but still fall short of recommended levels.


Q       Then what are the best ways for me to get more fiber?

A       Below is a table6 that shows some common foods and their fiber content.



Serving size

Total fiber



All-bran cereal

1/3 cup




Oatmeal, regular

1 cup




Shredded wheat

2/3 cup




Apple with skin

1 medium





1 cup





1/2 cup




Kidney beans

1/2 cup




Broccoli, raw

1/2 cup




Potato, with skin

1 medium




Carrots, raw

1 medium




Peas, green

1/2 cup




Bread, whole wheat

1 slice

2.59 g



Bread, white

1 slice





Eating foods with added resistant starch is another good way to get more fiber.  Resistant starch added during processing often increases the fiber in foods by up to 200%


Q       You’ve convinced me.  I’ll eat much more fiber, starting today.

A       Take it slowly.  If you increase the fiber in your diet too quickly, you may suffer from constipation and gas while your body adjusts.  Ramp up gradually, over about three weeks, and make sure to drink plenty of liquids (6-8 glasses a day) to balance a higher-fiber diet.



1    Chandalia M et al. Beneficial effects of high dietary fiber intake in patients with type 2 diabetes mellitus.  N Engl J Med. 2000; 342:1392-1398.

2    Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42

3    Bingham SA et al. Dietary fiber in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC); an observational study. The Lancet, 361: 9368, May 3, 2003.

4    Liu S, Willett WC, Manson JE, et al. Relation between changes in intakes of dietary fiber and grain products and changes in weight and development of obesity among middle-aged women. Am J Clin Nutr 2003;78:920–7

5    National Academy of Science Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids. September 5, 2002.

6    Adapted from Marlett, JA. Content and Composition of dietary fiber in 117 frequently consumed foods. J Am Diet Assoc 92:175-186, 1992. As reprinted by the University of Nebraska Cooperative Extension.


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