US Pharm. 2006;6:20-28.
Fiber is one of the most misunderstood
dietary components. Most people do not know how much fiber should be ingested
daily and which foods and supplements offer the best choices for fiber.
Pharmacists can provide information and products to help educate and assist
their patients in obtaining adequate intake of fiber.
Daily Fiber Recommendations
The average American has a daily
fiber intake of only 14 to 15 g. The daily recommendations for fiber intake
are higher than this, but they do vary slightly among population groups. For
instance, the American Dietetic Association recommends an intake of 20 to 35 g
for adults, 25 g daily for girls ages 9 through 18 years and 31 to 38 g for
boys ages 9 through 18. 1,2 The American Heart Association recommends 25 to 30
g daily.3 In 1994, the Institute for Cancer Prevention simplified fiber
intake guidelines for Americans as the "age + 5" rule.4 For
children age 2 years and older, the rule is that children should consume a
number of grams of fiber each day that equals their age plus 5 additional
grams. Thus, a 7-year-old should consume 12 g of fiber daily for optimal
health. This rule should be applied throughout adolescence until the person
reaches age 20, when the adult guidelines should be used.
The Definition and Categories of Fiber
At one time, fiber was defined as
any part of ingested plants that human enzymatic actions cannot digest, such
as cell wall components (e.g., waxes, lignin, pectin, celluloses).5However,
during the 1970s, the meaning of "fiber" gradually broadened to encompass and
embrace a physiological definition that has greater use for the medical
profession.5,6 The expanded definition of fiber now includes ingested
materials that are not components of plant cells (e.g., noncellulose plant
storage saccharides such as gums, modified celluloses, mucilages,
oligosaccharides, and beta-glucans), although they are still resistant to
degradation by human enzymes.7
Fibers are most usefully categorized for the
medical professional on the basis of their inability to dissolve in water. 8
Fibers that do dissolve in water (e.g., celluloses, pectin, other cell wall
components, as well as gums and psyllium) form gels, some of which have one or
more health benefits. Found in such foods as wheat, rice, maize, leafy
vegetables, peas, beans, and rhubarb, soluble fibers are able to sequester
cholesterol and fats, facilitating their elimination. Fibers that do not
dissolve in water bind water in the distal colon.9 Their sponge-like effect
bulks stools and also binds various materials such as bile acids and
carcinogens. Insoluble fibers are found in whole-grain cereals, breads,
vegetables, and wheat bran.
Fiber's Health Benefits
• Normalizing and Regulating Bowel Function:
Through its OTC Review, the FDA evaluated fiber products for use in regulating
bowel function. Several plant-derived bulk-forming fiber laxatives were found
to be safe and effective--such as psyllium, malt soup extract, and bran. Bran
and malt soup extract are not often marketed as nonprescription ingredients,
but psyllium is widely available in a variety of dosage forms and options. The
patient seeking a sugar-free psyllium product may use such products as
Metamucil Sugar-Free Powder (3 g of dietary fiber per teaspoonful) or Konsyl
Original Powder (6 g of psyllium per teaspoonful). Several non–plant-derived
ingredients also were found safe and effective as bulking agents, including
methylcellulose (e.g., Citrucel) and polycarbophil (e.g., FiberCon Caplets,
Phillips' FiberCaps, Konsyl Fiber Tablets).
A new fiber ingredient is being marketed in
a product known as Fibersure. The product contains inulin-type fructans,
chicory-derived carbohydrate polymers characterized by fructosyl– fructose
linkages.10 The linkages do not allow digestion in the upper digestive tract.
Thus, they are fermented in the colon, increasing the mass and water content
of stools. Inulin-type fructans are known as "functional foods" and thus have
not been evaluated by the FDA. Fiber supplementation is encouraged by
physicians and nurses to treat and prevent constipation.11,12
Little is known about hydrolyzed guar gum,
as found in Benefiber. The ingredient has not been approved by the FDA as a
nonprescription ingredient but is being marketed as a dietary supplement. The
National Academy of Sciences, in its Dietary Reference Intakes for Fiber,
states that guar gum has "little effect on fecal bulk or laxation."
13
• Weaning from Stimulants:
The FDA considers seven days to be the safe time limit for use of
laxatives without physician consultation. However, stimulant laxatives cause
many patients to become habituated to them because of their nonphysiologic and
drastic action; some patients might use laxatives for years once they become
reliant on them. This practice can lead to changes in the colon that are
carcinogenic and may result in death of colonic tissues located in the
myenteric plexus. Patients should be urged to replace habitual use of
stimulant laxatives with bulking agents. However, abrupt discontinuation in
habitual laxative overusers may result in an inability to evacuate the bowels.
The colon may not respond normally as a result of years of artificial
stimulation. The patient may benefit from a gradual withdrawal. In this
method, the pharmacist may recommend short-term stimulant use until the fiber
begins to exert its own effect. A combination of a stimulant and fiber (e.g.,
SennaPrompt) might be useful for a 30-day period to boost colonic function and
bridge the transition from stimulant addiction to natural facilitation of
bowel movements with fiber. After that period, the goal should be permanent
discontinuation of stimulants in favor of fiber intake.
• Lowering Cholesterol:
The 1990 Nutrition Labeling and Education Act gave FDA authority to regulate
health claims on food labels.14 As a result, manufacturers submitted research
attempting to demonstrate the effect of various fibers on health. Two fibers
have been proven safe and effective for the claims submitted. Beta-glucan
soluble fiber from whole oats met the standard for reduction of risk from
coronary heart disease.15,16 Psyllium husk is also able to reduce the risk of
coronary heart disease as it contains a soluble fiber similar to beta-glucan.
17,18 Researchers quantified this outcome by determining the effect of
psyllium (5 g three times daily) in lowering cholesterol as an adjunct to 10
mg of simvastatin, as compared to doubling the dose of simvastatin to 20 mg.19
They discovered that dietary supplementation with psyllium in patients taking
10 mg of simvastatin was as effective in lowering cholesterol as 20 mg of
simvastatin alone. As a result of this research and FDA findings, pharmacists
can recommend ingesting psyllium supplements daily to consumers who wish to
attain regularity of bowel movements while simultaneously lowering their risk
of coronary heart disease.
• Weight Reduction:
The popular media has given ample coverage to the epidemic of obesity in
America. Almost 100 million Americans are either obese or overweight.20
The figures climb each year, so that the toll of obesity will also continue to
rise. Obesity has been linked to such morbid conditions as osteoarthritis in
weight-bearing joints, type 2 diabetes, heart disease, cancer, and many other
conditions. While hundreds of dietary supplements purported to be obesity
cures are launched each year, the rising incidence of the condition attests to
their inefficacy. The cure for obesity is actually quite simple. The
overweight patient must eat less and exercise more, beginning immediately and
continuing over the span of a lifetime.
Stomach distension (feeling full) signals a
person to stop eating. It is in this area that fiber can yield lasting
benefits through several mechanisms. Fiber is a bulky food, more difficult to
digest than fatty foods, fried foods, and candies. Once ingested, fiber
enhances satiety and prolongs satiation after a meal through distending the
stomach and by prolonging retention of gastric contents.21 The stomach is
distended after a fiber-containing meal because it promotes secretion of
saliva and of gastric acids, both of which distend the stomach. Ingestion of
fiber must be accompanied by water intake, which further serves to distend the
stomach during a meal.22 Prolonging gastric retention decreases the absorption
rate of nutrients, so that hunger does not return as rapidly.
Fiber also yields dietary benefit through
energy displacement or energy dilution. A person who ingests little fiber in
an average day usually has a diet of high-energy foods such as fats. However,
the bulk that fiber adds to the diet makes it impossible to eat the same
quantity of high-energy foods. Research bears this out. If a patient adds 14 g
of fiber to the diet, energy intake will be reduced by approximately 10%.22
Further, observational studies of obese people and those who are thin confirm
that thin people ingest more fiber and obese people ingest more high-fat
foods.
Researchers explored the link between
dietary fiber/fat intake and excess weight in young and middle-aged adults.21
They discovered that only 5% of the sample consumed adequate fiber. Further,
in women, consumption of a low-fiber, high-fat diet was associated with the
highest incidence of obesity when compared to those consuming a high-fiber,
low-fat diet.
• Prevention of Colon Cancer:
Fiber may help prevent colon cancer. The possible link stems from
observational studies in the 1970s demonstrating that natives of Africa
consuming high-fiber diets had reduced risk of colorectal carcinoma.23
Studies carried out to explore this link have been contradictory. Some seem to
confirm a protective effect, but others show little to no effect.24
There is little risk to fiber consumption. Therefore, with no clearly negative
data about fiber, it makes sense to increase fiber intake just in case the
positive studies did reveal an actual link. The patient will also experience
the ancillary benefits of fiber consumption, such as reduction in cholesterol
(with psyllium), prevention of constipation, and reducing risk of hemorrhoids.
Fiber and the Glycemic Index
Fiber is especially beneficial in
patients with diabetes. Investigators administered 5.1 g of psyllium as a meal
supplement to patients with type 2 diabetes, finding that it reduced the
postprandial glucose and insulin concentrations.25 They concluded that
psyllium was safe, well tolerated, and improved glycemic control.
References
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April 11, 2006.
3. Fiber. American Heart Association.
Available at: www.americanheart.org/presenter.jhtml?identifier=4574. Accessed
April 11, 2006.
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