Fibers: why are they essential?

Dietary fiber is not digested by our bodies. The fibers have an effective appetite suppressant effect and facilitate transit. But, then, where to find the fibers, and what are their benefits? Focus on fibers.

What is Fiber?

Dietary fiber represents the carbohydrates and lignin that occur naturally in plant foods and are not digested and absorbed by the digestive system.

Functional fibers

There is also another type of fiber called functional fiber which is actually carbohydrates that have been isolated, extracted, and/or purified.

To be part of the range of functional fibers, they must have beneficial effects on the body. Functional fibers are not absorbed or digested by the digestive system in the same way as dietary fibers.  

The role of fibers

Fiber has different physiological roles to play including regulating gastrointestinal function, lowering cholesterol levels, and managing glycemia (blood sugar levels).

They also contribute to the feeling of satiety, which can help with weight management by reducing energy intake. There are many, but not all, studies that claim adequate fiber intake protects against colon cancer.

There are two types of fiber in plant foods:

  • Soluble (viscous) fibers have the property of reducing blood glucose and cholesterol levels.
  • insoluble fiber increases fecal volume to regulate bowel function.

Most plant foods contain both types of fiber. However, the amount of each type of fiber varies between foods.

Foods Predominantly Insoluble FiberSoluble Fiber Predominant Foods
Wheat bran and wheat cerealsPsyllium and fortified cereals
Whole grains and derivativesOat bran and oat cereal (oatmeal)
Vegetables: cauliflower, kale, green peas, spinach, turnip, green beansLegumes: kidney beans, peas
Fruits: raspberries, apples, pears, bananas, blueberries, strawberriesFruits: orange, grapefruit, mango, dried prunes
Nuts and seeds: almonds, peanutsVegetables: asparagus, Brussels sprouts, carrots, onion
Legumes in generalBarley

Daily fiber requirements

Total fiber requirements have been established based on an intake that, according to scientific data, is protective against cardiovascular disease and diabetes. 

AgeAdequate intake (AI)
Babies 0 – 6 monthsND
Babies 7 – 12 monthsND
Babies 1 – 3 years old19 g
Children 4-8 years old25 g
Boys 9 – 13 years old31 g
Girls 9 – 13 years old26 g
Boys 14 – 18 years old38 g
Girls 14 – 18 years old26 g
Men 19 – 50 years old38 g
Women 19 – 50 years old25 g
Men 50 and over30 g
Women 50 and over21 g
Pregnant women28 g
Nursing women29 g

*Recommended nutritional intake
**AMT: tolerable upper intake

Food sources of fiber

The main sources of fiber are vegetables and fruits as well as grain products, legumes, and nuts. 

FoodPortionsQuantities (g)
Cooked legumes250ml (1 cup)12 – 17
Breakfast cereals, 100% wheat bran30 g (1 oz)10
Soybeans, fresh (edamame), boiled250ml (1 cup)8
Raspberries125ml (1/2 cup)4-6
Boiled artichoke1 medium (120g)5
Dried prunes, cooked75 ml pitted (80 g)5
Pear with peel1 medium (166g)5
Green peas, cooked125ml (1/2 cup)4-5
blackberries125ml (1/2 cup)4
canned pumpkin125ml (1/2 cup)4
Dates or dried figs60ml (1/4 cup)4
Potato with skin, baked1 medium (150g)4
Boiled spinach125ml (1/2 cup)4
Almonds roasted in oil or dry60ml (1/4 cup)4
Boiled sweet potato1 medium (151g)4
Apple with peel1 medium (138g)3
Winter squash, cooked125ml (1/2 cup)3
Papaya1/2 fruit (153 g)3
Brussels sprouts, cooked4 choux (84 g)3
blueberries125ml (1/2 cup)2-3

Tips for increasing your fiber intake 

Replace refined grain products with brown rice, pasta, or bread made with whole grains;

consume more fruits containing fiber: apples and pears with their peel, raspberries and blackberries, dried fruits (prunes, apricots, and dates);

choose fiber-rich vegetables more often: artichokes, peas, beets, carrots, broccoli, cabbage, Brussels sprouts, corn, turnips, and potatoes with the skin on;

eat more often legumes, excellent sources of dietary fiber: white or red beans, lentils, lima beans, chickpeas;

add lentils or beans to soups, casseroles, and salads. Cook a vegetarian chili;

spread hummus on a slice of whole-grain bread or high-fiber crackers as a snack;

as a snack, choose cereals rich in fiber (4 g of fiber per serving and read) or a homemade muffin rich in fiber;

when making muffin recipes, replace white flour with whole wheat flour. Add ground flax seeds or wheat or oat bran;

add wheat or oat bran, flax, or chia seeds to your yogurts and compotes;

add soybeans to soups, stir-fries, or salads;

as a snack, eat a small handful of dried fruit and nuts;

read food labels and choose bread, bagels, pitas, tortillas, and crackers that contain 2-4 g of fiber per serving.

It is very important to increase your fiber intake gradually and to drink plenty of water to avoid certain gastrointestinal symptoms.

Potential fiber interactions

A very high fiber intake could interfere with the absorption of various nutrients including calcium, magnesium, iron, and zinc.

However, when there is no deficiency of these nutrients in the diet, adequate fiber intake does not appear to compromise the stores of these nutrients.

Fiber deficiency and excess

fiber deficiency

As fiber is not an essential nutrient, a low intake does not bring deficiency symptoms. However, insufficient fiber intake can lead to constipation due to low fecal volume.

Excess fiber

Excessive fiber intake has no deleterious effect apart from certain gastrointestinal symptoms such as bloating or gas. Overuse is very unlikely.

Image Credit: Photo by Jannis Brandt on Unsplash

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