Although fiber has no nutritional value, it plays an extremely important role in maintaining good health.
There are two types of fiber: soluble fiber, which is a part of fruits, vegetables, oats, nuts and legumes. It’s made of the components of plant cells, which swell in water. Soluble fiber decomposes into simpler components through the effect of colon bacteria. The most common source of soluble fiber are psylium seeds. The main effect of soluble fiber is the absorption of excess water from intestines and also reduction of cholesterol in the blood.
Insoluble fiber is found in cereals and grains. It consists of various components of cell walls and lignin, which, although binding water, do not swell. Our digestive system is unable to decompose it, thus it passes through the digestive tract undigested. Regular intake of insoluble fiber (e.g. cellulose) supports intestinal function and elimination of of carcinogenic and toxic substances.
Long-term lack of fiber intake can lead to diabetes, various heart diseases, digestive problems and hemorrhoids. The average daily fiber intake for an adult should be between 25-35 g, while most people do not reach half of this value.
Fiber is a part of many different products designed for weight loss – due to absorbed water it fills the stomach and reduces appetite. It also extends the digestion of food in the stomach and causes a feeling of satiety.
Some foods high in fiber – such as flax seed – contain plant estrogens (i.e. lignans) that reduce the risk of breast cancer.
But you have to be cautious in some cases – a large, sudden intake of fiber can cause bloating and abdominal pain. Some sources of fiber – such as legumes – can cause flatulence.
The fiber content in some foods
| Food | Soluble fiber | Insoluble fiber | Total |
|---|---|---|---|
| Apples | 5.6 to 5.8 | 7.2 to 7.5 | 12.8 to 13.3 |
| Peaches | 4.1 to 7.1 | 3.4 to 6.4 | 7.5 to 13.5 |
| Garden Strawberries | 5.1 to 7.7 | 6.8 to 10.6 | 11.9 to 18.3 |
| Oranges | 6.5 to 8.9 | 3.9 to 5.2 | 10.4 to 15.0 |
| Carrots | 4.4 to 14.9 | 10.4 to 11.1 | 14.8 to 26.0 |
| Cabbage | 13.5 to 16.6 | 4.2 to 20.8 | 27.6 to 37.4 |
| Tomatoes | 0.8 to 3.5 | 3.2 to 12.8 | 6.7 to 13.6 |
| Green Peas | 5.9 | 15.0 | 20.9 |
| Beans | 7.2 to 12.4 | 9.1 to 9.6 | 16.8 to 21.5 |
| Raw Potatoes | 2.8 to 3.5 | 2.4 to 3.2 | 5.2 to 6.7 |
| White Wheat Flour | 2.0 | 1.2 | 3.2 |
| Whole Grain Wheat Flour | 2.6 | 7.7 | 10.3 |
| Bread Wheat | 1.6 to 2.7 | 1.1 to 2.9 | 2.7 to 5.6 |
| Rye Bread | 6.7 | 6.6 | 13.3 |
| Cornflakes | 0.2 to 0.4 | 0.5 | 0.7 to 0.9 |
Components of dietary fiber in certain foods
| Food | Cellulose | Other non-recoverable polysaccharides | Lignin | |||
|---|---|---|---|---|---|---|
| Average | Range | Average | Range | Average | Range | |
| Fruit | 19.7 | 9 to 33 | 62.9 | 46 to 78 | 17.4 | 1 to 38 |
| Vegetables | 31.5 | 23 to 42 | 65.6 | 52 to 76 | 3.0 | 0 to 13 |
| Cereals | 17.4 | 12 to 22 | 75.7 | 71 to 82 | 6.7 | 0 to 15 |
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