Fiber
Definition
Fiber is found only in foods of plant origin. It
occurs in the skins, seeds, leaves and roots of fruits
and vegetables, and in the germ and bran layers of
grains. Pectins, lignans, cellulose, gums and mucilages
are all different forms of fiber found in these foods.
Because humans lack the digestive enzymes to break
down fiber, it passes through the digestive tract largely
unchanged.Purpose
Depending on the type, fiber may either slow
down or speed up the passage of food through the
digestive tract. It contributes to stool bulk and stim-
ulates the colon walls to contract. Foods rich in solu-
ble fiber are often recommended to help improve
blood glucose and cholesterol levels, while diets con-
taining high amounts of insoluble fiber are known to
contribute to bowel regularity and the prevention of
diverticular disease. Since high-fiber diets tend to be
satisfying but relatively low in calories, they are often
promoted for weight management.Description
Dietary fiber belongs to one of two types, depend-
ing on whether or not it is able to dissolve inwater.
Fiber that dissolves in water is calledsoluble, while
fiber that cannot be dissolved in water is known as
insoluble. Upon ingestion, soluble fiber dissolves in the
fluids secreted by the digestive tract, forming a gel.
This gel moves slowly through the digestive tract, thus
slowing the rate of digestion and absorption. Diets
containing large amounts of soluble fiber have been
shown to stabilize blood sugar levels in people with
diabetes, and have been shown to reduce blood levels
of unhealthy (LDL) cholesterol. Foods high in soluble
fiber include beans, lentils, oats, psyllium, citrus fruits,
barley and apples. In contrast, insoluble fiber acts as
roughage. It contributes to stool bulk and promotes
regularity. Foods rich in insoluble fiber include wheat
bran, whole grains, dried beans, nuts, seeds, and those
fruits and vegetables with an edible outer skin or seeds.
In 2001, the Food and Nutrition Board of the
Institute of Medicine established its first recommen-
dations for fiber intake. The recommendations are
based on the findings of numerous studies showing a
reduced risk of heart disease and type 2 diabetes with a
daily fiber intake of approximately 14 grams for every
1,000 calories consumed. For adults who are 50 yearsof age and younger, the recommended fiber intake is
38 g/day for men and 25 g/day for women. For adults
over 50 years of age, the recommendation is 30 g/day
for men and 21 g/day for women.
On average, North Americans consume less than
50% of the dietary fiber recommended for good
health.Potential Benefits
A high fiber intake promotes bowel health by pre-
venting constipation and diverticular disease.FiberAge Recommended Intakes (g/day)
Children 1 yr. Not established
Children 1–3 yrs. 19
Children 4–8 yrs. 25
Boys 9–13 yrs. 31
Girls 9–13 yrs. 26
Boys 14–18 yrs. 38
Girls 14–18 yrs. 26
Men 19–50 yrs. 38
Women 19–50 yrs. 25
Men 50 yrs. 30
Women 50 yrs. 21
Pregnant women 28
Breastfeeding women 29
Food Fiber (g)
Beans, lima, fresh, cooked, ½ cup 6.6
Beans, baked, canned, plain, ½ cup 6.3
Beans, black, cooked, ½ cup 6.1
Beans, kidney, fresh, cooked, ½ cup 5.7
Winter squash, cooked, 1 cup 5.7
Spaghetti, whole wheat, plain, 1 cup 5.6
Cereal, bran flake, ¾ cup 5.3
Cereal, shredded wheat, 1 cup 5.2
Pear, raw, 1 med. 5.1
Turnips, cooked, ½ cup 4.8
Rice, brown, cooked, 1 cup 3.5
Apple, raw, with skin, 1 med. 3.3
Oatmeal, plain, cooked, ¾ cup 3.0
Broccoli, fresh, cooked, ½ cup 2.6
Summer squash, cooked, 1 cup 2.5
Carrot, fresh, cooked, ½ cup 2.3
Potato, fresh, cooked, 1 2.3
Spinach, fresh, cooked, ½ cup 2.2
Brussels sprouts, fresh, cooked, ½ cup 2.0
Bread, whole-wheat, 1 slice 1.9
Tangerine, raw, 1 med. 1.9
Cauliflower, fresh, cooked, ½ cup 1.7
Cabbage, fresh, cooked, ½ cup 1.5
Peach, raw, 1 med. 1.5
Asparagus, fresh, cooked, 4 spears 1.2
Romaine lettuce, 1 cup 1.2
Peanuts, dry roasted, 1 tbsp. 1.1
Tomato, raw, 1 1.0
Rice, white, cooked, 1 cup 0.6
Almonds, slivered, 1 tbsp. 0.6
g gram(Illustration by GGS Information Services/Thomson Gale.)Fiber