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.
Fiber, what is it?
Dietary fiber represents the carbohydrates and lignin that occur naturally in plant foods and are not digested and absorbed by the digestive system.
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 Fiber||Soluble Fiber Predominant Foods|
|Wheat bran and wheat cereals||Psyllium and fortified cereals|
|Whole grains and derivatives||Oat bran and oat cereal (oatmeal)|
|Vegetables: cauliflower, kale, green peas, spinach, turnip, green beans||Legumes: kidney beans, peas|
|Fruits: raspberries, apples, pears, bananas, blueberries, strawberries||Fruits: orange, grapefruit, mango, dried prunes|
|Nuts and seeds: almonds, peanuts||Vegetables: asparagus, Brussels sprouts, carrots, onion|
|Legumes in general||Barley|
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.
|Age||Adequate intake (AI)|
|Babies 0 – 6 months||ND|
|Babies 7 – 12 months||ND|
|Babies 1 – 3 years old||19 g|
|Children 4-8 years old||25 g|
|Boys 9 – 13 years old||31 g|
|Girls 9 – 13 years old||26 g|
|Boys 14 – 18 years old||38 g|
|Girls 14 – 18 years old||26 g|
|Men 19 – 50 years old||38 g|
|Women 19 – 50 years old||25 g|
|Men 50 and over||30 g|
|Women 50 and over||21 g|
|Pregnant women||28 g|
|Nursing women||29 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.
|Cooked legumes||250ml (1 cup)||12 – 17|
|Breakfast cereals, 100% wheat bran||30 g (1 oz)||10|
|Soybeans, fresh (edamame), boiled||250ml (1 cup)||8|
|Raspberries||125ml (1/2 cup)||4-6|
|Boiled artichoke||1 medium (120g)||5|
|Dried prunes, cooked||75 ml pitted (80 g)||5|
|Pear with peel||1 medium (166g)||5|
|Green peas, cooked||125ml (1/2 cup)||4-5|
|blackberries||125ml (1/2 cup)||4|
|canned pumpkin||125ml (1/2 cup)||4|
|Dates or dried figs||60ml (1/4 cup)||4|
|Potato with skin, baked||1 medium (150g)||4|
|Boiled spinach||125ml (1/2 cup)||4|
|Almonds roasted in oil or dry||60ml (1/4 cup)||4|
|Boiled sweet potato||1 medium (151g)||4|
|Apple with peel||1 medium (138g)||3|
|Winter squash, cooked||125ml (1/2 cup)||3|
|Papaya||1/2 fruit (153 g)||3|
|Brussels sprouts, cooked||4 choux (84 g)||3|
|blueberries||125ml (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
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.
Excessive fiber intake has no deleterious effect apart from certain gastrointestinal symptoms such as bloating or gas. Overuse is very unlikely.