Viscous Fibers Promote beneficial Physiological effects

[Guest guest]

Dietary fiber is undoubtedly one of the most talked about nutrients

for health promotion and disease prevention. In fact, dietary fiber

is the focus of two FDA-approved health claims that appear on foods

labels touting the benefits of high fiber foods for the prevention

of heart disease and certain types of cancer.

 

Since the early 1950's, when the term " fiber " first began to be used

in scientific journals, there has been considerable controversy

among food scientists, nutritionists, and medical experts about the

exact definition of dietary fiber.

 

In fact, even the United States Food and Drug Administration, the

federal agency responsible for overseeing food labeling, has no

formal, written definition of dietary fiber.

 

For food labeling purposes and the determination of health claims,

the FDA has adopted the analytical methods that the Association of

Official Analytical Chemists uses for defining dietary fiber.

 

Although most experts agree that a key defining characteristic of

dietary fiber is that it's derived from the edible parts of plants

that are not broken down by human digestive enzymes, many people

believe that this definition is too ambiguous and that a more clear,

internationally-accepted definition is needed to ensure that the

total fiber counts on food labels are consistent and accurate.

 

In recent years there has been a movement among various

organizations to include the physiological benefits of dietary fiber

in a new definition.

 

For example, the American Association of Cereal Chemists proposed a

new definition of dietary fiber that includes the statement " Dietary

fibers promote beneficial physiological effects including laxation

and/or blood cholesterol attenuation and/or blood glucose

attenuation. "

 

In addition, the Institute of Medicine at the National Academy of

Sciences (the organization responsible for issuing Recommended

Dietary Allowances) has proposed a new definition that

differentiates between dietary fiber and added fiber.

 

According to this definition, dietary fiber consists of

nondigestible carbohydrates and lignin that are intrinsic and intact

in plants.

 

Added fiber, which refers to fiber that is added to foods

during " food processing " , consists of isolated nondigestible

carbohydrates that have proven beneficial physiological effects in

humans.

 

For food labeling purposes, the Institute of Medicine defines Total

Fiber as the sum of Dietary Fiber and Added Fiber.

 

Despite the controversy surrounding the exact definition of dietary

fiber, experts agree on one important thing - dietary fiber is an

important weapon in the fight against heart disease, colon cancer,

diabetes, and obesity.

 

Categories of Dietary Fiber

 

Cellulose, found in bran, legumes, peas, root vegetables, cabbage

family, outer covering of seeds, and apples

Hemicellulose, found in bran and whole grains

Polyfructoses (Inulin and Oligofructans)

Galactooligosaccharides

Gums, found oatmeal, barley, and legumes.

Mucilages

Pectins, found in apples, strawberries, and citrus fruits

Lignin, found in root vegetables, wheat, fruits with edible seeds

(such as strawberries)

Resistant Starches, found in ripe bananas, potatoes

How it Functions

 

What is the function of dietary fiber?

Until very recently, the functions of a specific type of fiber were

determined by whether or not the fiber was classified as soluble or

insoluble. Soluble fibers, such as the type found in oat bran, are

known to reduce blood cholesterol levels and normalize blood sugar

levels.

 

On the other hand, insoluble fiber, such as the type found in wheat

bran, are known to promote bowel regularity. Many commonly used

plant sources of fiber contain both soluble and insoluble fibers.

Psyllium husks, for example, contain a mixture of 70% soluble and

30% insoluble fibers. Despite the widespread use of the

terms " soluble " and " insoluble " to describe the health benefits of

dietary fiber, many medical and nutrition experts contend that these

terms do not adequately describe the physiological effects of all

the different types of fiber.

 

These experts are now proposing the use of the terms " viscous "

and " fermentability " in place of soluble and insoluble to describe

the functions and health benefits of dietary fiber.

 

Reducing Cholesterol Levels

Like soluble fibers, viscous fibers lower serum cholesterol by

reducing the absorption of dietary cholesterol.

 

In addition, viscous fibers complex with bile acids, which are

compounds manufactured by the liver from cholesterol that are

necessary for the proper digestion of fat.

 

After complexing with bile acids, the compounds are removed from

circulation and do not make it back to the liver.

As a result, the liver must use additional cholesterol to

manufacture new bile acids. Bile acids are necessary for normal

digestion of fat. Soluble fiber may also reduce the amount of

cholesterol manufactured by the liver.

 

Normalizing Blood Sugar Levels

Viscous fibers also help normalize blood glucose levels by slowing

the rate at which food leaves the stomach and by delaying the

absorption of glucose following a meal. Viscous fibers also increase

insulin sensitivity.

 

As a result, high intake of viscous fibers play a role in the

prevention and treatment of type 2 diabetes.

 

In addition, by slowing the rate at which food leaves the stomach,

viscous fibers promote a sense of satiety, or fullness, after a

meal, which helps to prevent overeating and weight gain.

 

Promoting Bowel Regularity

Certain types of fiber are referred to as fermentable fibers because

they are fermented by the " friendly " bacteria that live in the large

intestine.

 

The fermentation of dietary fiber in the large intestine produces a

short-chain fatty acid called butyric acid, which serves as the

primary fuel for the cells of the large intestine and helps maintain

the health and integrity of the colon.

 

Two other short-chain fatty acids produced during fermentation,

propionic and acetic acid are used as fuel by the cells of the liver

and muscles.

 

In addition, propionic acid may be responsible, at least in part,

for the cholesterol-lowering properties of fiber.

 

In animal studies, propionic acid has been shown to inhibit HMG-CoA

reductase, an enzyme involved in the production of cholesterol by

the liver. By lowering the activity of this enzyme, blood

cholesterol levels may be lowered.

 

In addition, fermentable fibers help maintain healthy populations of

friendly bacteria. In addition to producing necessary short-chain

fatty acids, these bacteria play an important role in the immune

system by preventing pathogenic (disease-causing) bacteria from

surviving in the intestinal tract.

 

As is the case with insoluble fiber, fibers that are not fermentable

in the large intestine help maintain bowel regularity by increasing

the bulk of the feces and decreasing the transit time of fecal

matter through the intestines.

 

Bowel regularity is associated with a decreased risk for colon

cancer and hemorrhoids (when the hemorrhoids are related to

straining and constipation).

 

Deficiency Symptoms

 

What are deficiency symptoms for dietary fiber?

There is no identifiable, isolated deficiency disease caused by lack

of fiber in the diet. However, research clearly indicates that low

intake of dietary fiber (less than 20 grams per day) over the course

of a lifetime is associated with development of numerous health

problems including constipation, hemorrhoids, colon cancer, obesity

and elevated cholesterol levels.

 

 

Excessive intake of nonfermentable fiber, typically in supplemental

form, may lead to mineral deficiencies by reducing the absorption or

increasing the excretion of minerals, especially when mineral intake

is too low or when mineral needs are increased such as during

pregnancy, lactation, or adolescence.

 

Impact of Cooking, Storage and Processing

 

How do cooking, storage, or processing affect dietary fiber?

Many whole foods contain 5 or more grams of fiber, and in their

whole, unprocessed form, would be highly supportive of health. When

foods are processed, however, most or all of this fiber is often

lost.

 

For example, most breads sold nationally in the United States use a

60% extraction process in which 60% of the original wheat grain is

kept in the flour, but 40% is discarded. The discarded part of the

wheat includes the bran and the germ; these two components of the

grain contain virtually all of its fiber.

 

As a result, 60% extraction wheat flour contains almost no fiber,

even though the whole, unprocessed wheat grain contains an ample

amount. Fruit juices and vegetable juices are also good examples of

products which started out high-fiber in their whole, unprocessed

state but ended up with virtually no fiber as a result of

processing.

 

Factors that Affect Function

 

What factors might contribute to a deficiency of dietary fiber?

Even though fiber is often defined as the " undigestable " part of

food, a certain amount of healthy digestive function is important

for realizing the health benefits of this nutrient.

 

Inadequate chewing can prevent the health benefits of fiber from

being realized, since fibers that cannot be solubilized (like

lignins, celluloses, and some hemicelluloses) require extra chewing

in order to participate in biochemical processes.

 

Drug-Nutrient Interactions

 

What medications affect dietary fiber?

Dietary fiber, especially the fiber found in fruit, beans, and oat

bran, reduces the absorption of a class of cholesterol-lowering

medications called HMG-CoA reductase inhibitors (for example,

lovastatin) by binding to the drug in the gastrointestinal tract.

Dietary fiber decreases the absorption of hydralazine, digoxin, and

lithium.

Diets high in dietary fiber may improve glucose control in people

with type 2 diabetes, thereby reducing the dose of insulin or oral

glucose lowering medications needed to control blood sugar.

Certain medications, including pain medications (for example,

codeine) and calcium channel blockers (for example, verapamil) can

cause constipation.

Increased intake of dietary fiber can reduce the constipation caused

by these medications.

 

Nutrient Interactions

 

How do other nutrients interact with dietary fiber?

Foods high in nonfermentable fiber, or the fiber that passes all the

way through the intestines unchanged, may reduce the absorption

and/or increase the excretion of several minerals, including calcium

and iron.

 

Health Conditions

 

What health conditions require special emphasis on dietary fiber?

A diet high in fiber may play a role in the prevention and/or

treatment of the following health conditions:

 

Breast cancer

Cardiovascular disease

Colon cancer

Constipation

Diabetes

Diverticulitis

Gallstones

High cholesterol

Irritable bowel syndrome

Obesity

Syndrome X

 

 

Food Sources

 

 

Cinnamon, ground 2 tsp 11.8 2.48 9.9 15.1 very good

Turnip greens, cooked 1 cup 28.8 5.04 20.2 12.6 excellent

Basil, dried, ground 2 tsp 7.5 1.20 4.8 11.5 good

Coriander seeds 2 tsp 9.9 1.40 5.6 10.2 very good

Oregano, dried, ground 2 tsp 9.2 1.28 5.1 10.1 very good

Raspberries 1 cup 60.3 8.34 33.4 10.0 excellent

Thyme, dried, ground 2 tsp 7.9 1.08 4.3 9.8 good

Mustard greens, boiled 1 cup 21.0 2.80 11.2 9.6 excellent

Rosemary, dried 2 tsp 7.3 0.92 3.7 9.1 good

Romaine lettuce 2 cup 15.7 1.90 7.6 8.7 very good

Cauliflower, boiled 1 cup 28.5 3.35 13.4 8.5 excellent

Collard greens, boiled 1 cup 49.4 5.32 21.3 7.8 excellent

Broccoli, steamed 1 cup 43.7 4.68 18.7 7.7 excellent

Cloves, dried, ground 2 tsp 14.2 1.52 6.1 7.7 very good

Celery, raw 1 cup 19.2 2.04 8.2 7.7 very good

Swiss chard, boiled 1 cup 35.0 3.68 14.7 7.6 excellent

Cabbage, shredded, boiled 1 cup 33.0 3.45 13.8 7.5 very good

Spinach, boiled 1 cup 41.4 4.32 17.3 7.5 very good

Chili pepper, dried 2 tsp 25.5 2.64 10.6 7.5 very good

Black pepper 2 tsp 10.9 1.12 4.5 7.4 good

Fennel, raw, sliced 1 cup 27.0 2.70 10.8 7.2 very good

Green beans, boiled 1 cup 43.8 4.00 16.0 6.6 very good

Eggplant, cooked, cubes 1 cup 27.7 2.48 9.9 6.4 very good

Cayenne pepper, dried 2 tsp 11.2 0.96 3.8 6.2 good

Cranberries 0.50 cup 23.3 1.99 8.0 6.2 very good

Strawberries 1 cup 43.2 3.31 13.2 5.5 very good

Bell peppers, red, raw, slices 1 cup 24.8 1.84 7.4 5.3 very good

Winter squash, baked, cubes 1 cup 80.0 5.74 23.0 5.2 very good

Kale, boiled 1 cup 36.4 2.60 10.4 5.1 very good

Split peas, cooked 1 cup 231.3 16.27 65.1 5.1 very good

Summer squash, cooked, slices 1 cup 36.0 2.52 10.1 5.0 very good

Carrots, raw 1 cup 52.5 3.66 14.6 5.0 very good

Lentils, cooked 1 cup 229.7 15.64 62.6 4.9 very good

Brussel sprouts, boiled 1 cup 60.8 4.06 16.2 4.8 very good

Asparagus, boiled 1 cup 43.2 2.88 11.5 4.8 very good

Black beans, cooked 1 cup 227.0 14.96 59.8 4.7 very good

Green peas, boiled 1 cup 134.4 8.80 35.2 4.7 very good

Pinto beans, cooked 1 cup 234.3 14.71 58.8 4.5 very good

Cucumbers, slices, with peel 1 cup 13.5 0.83 3.3 4.4 good

Lima beans, cooked 1 cup 216.2 13.16 52.6 4.4 very good

Turmeric, powder 2 tsp 16.0 0.96 3.8 4.3 good

Flaxseeds 2 tbs 95.3 5.41 21.6 4.1 very good

Kiwifruit 1 each 46.4 2.58 10.3 4.0 very good

Wheat, bulgur, cooked 1 cup 151.1 8.19 32.8 3.9 very good

Tomato, ripe 1 cup 37.8 1.98 7.9 3.8 very good

Oranges 1 each 61.6 3.13 12.5 3.7 very good

Kidney beans, cooked 1 cup 224.8 11.33 45.3 3.6 very good

Barley, cooked 1 cup 270.0 13.60 54.4 3.6 very good

Apricots 1 each 16.8 0.84 3.4 3.6 good

Blueberries 1 cup 81.2 3.92 15.7 3.5 very good

Onions, raw 1 cup 60.8 2.88 11.5 3.4 very good

Garbonzo beans (chickpeas), cooked 1 cup 269.0 12.46 49.8 3.3 good

Papaya 1 each 118.6 5.47 21.9 3.3 good

Apples 1 each 81.4 3.73 14.9 3.3 good

Grapefruit 0.50 each 36.9 1.69 6.8 3.3 good

Beets, Boiled 1 cup 74.8 3.40 13.6 3.3 good

Navy beans, cooked 1 cup 258.4 11.65 46.6 3.2 good

Figs, fresh 8 oz-wt 167.8 7.48 29.9 3.2 good

Rye, whole grain, uncooked 0.33 cup 188.7 8.22 32.9 3.1 good

Pear 1 each 97.9 3.98 15.9 2.9 good

Soybeans, cooked 1 cup 297.6 10.32 41.3 2.5 good

Yam (Dioscorea species), cubed, cooked 1 cup 157.8 5.30 21.2 2.4

good

Sweet potato, baked, with skin 1 each 95.4 3.14 12.6 2.4 good

Avocado, slices 1 cup 235.1 7.30 29.2 2.2 good

Mustard seeds 2 tsp 35.0 1.08 4.3 2.2 good

Prunes 0.25 cup 101.6 3.02 12.1 2.1 good

Buckwheat, cooked 1 cup 154.6 4.54 18.2 2.1 good

Shiitake mushrooms, raw 8 oz-wt 87.2 2.49 10.0 2.1 good

Olives 1 cup 154.6 4.30 17.2 2.0 good

Oats, whole grain, cooked 1 cup 145.1 3.98 15.9 2.0 good

Plum 1 each 36.3 0.99 4.0 2.0 good

Crimini mushrooms, raw 5 oz-wt 31.2 0.85 3.4 2.0 good

Miso 1 oz 70.8 1.86 7.4 1.9 good

Banana 1 each 108.6 2.83 11.3 1.9 good

Corn, yellow, cooked 1 cup 177.1 4.60 18.4 1.9 good

Pineapple 1 cup 76.0 1.86 7.4 1.8 good

Cantaloupe, cubes 1 cup 56.0 1.28 5.1 1.6 good

Potato, baked, with skin 1 cup 133.0 2.93 11.7 1.6 good

Sesame seeds 0.25 cup 206.3 4.24 17.0 1.5 good

 

 

Public Health Recommendations

 

What are current public health recommendations for dietary fiber?

In its most recent 2005 public health recommendations for fiber

(published as the Dietary Reference Intakes for Energy,

Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and

Amino Acids (Macronutrients), National Academies Press, 2005), the

National Academy of Sciences established an Adequate Intake (AI)

level of 38 grams of total daily fiber for males 19-50 years of age

and 25 grams for women in this same age range. It also noted that

individuals in this age range in the United States only get about

half this much fiber each day.

 

References

 

American Association of Cereal Chemists. The definition of dietary

fiber. Cereal Foods World 2001; 46(3), 112-127

American Dietetic Association. Health implications of dietary fiber -

- Position of the ADA. Journal of the American Dietetic Association

1997; 97:1157-1159

Burton-Freeman B. Dietary fiber and energy regulation. J Nutr 2000

Feb;130(2S Suppl):272S-5S, PMID: 15360

Cohen LA. Dietary fiber and breast cancer. Anticancer Res 1999 Sep-

1999 Oct 31;19(5A):3685-8, PMID: 15370

Davy BM and Melby CL. The effect of fiber-rich carbohydrates on

features of Syndrome X. J Am Diet Assoc 2003 Jan;103(1):86-96 2003

Fernandez ML. Soluble fiber and nondigestible carbohydrate effects

on plasma lipids and cardiovascular risk. Curr Opin Lipidol 2001

Feb;12(1):35-40 2001

Flamm G, Glinsmann W, Kritchevsky D, et al. Inulin and oligofructose

as dietary fiber: a review of the evidence. Crit Rev Food Sci Nutr

2001 Jul;41(5):353-62, PMID: 15310

Garcia Peris P, Camblor Alvarez M. [Dietary fiber: concept,

classification and current indications]. Nutr Hosp 1999 May;14 Suppl

2:22S-31S, PMID: 15380