Insoluble fiber is the water-insouble portion of dietary fiber. It does not soak in or hold water.
However, it irritates the bowels and stimulates it to release water and mucous. This effect in turn makes stool soft and bulky. The coarser the insoluble fiber particles in the intestine the more laxative benefit it has.
Insoluble fiber passes the small intestine mostly intact, undigested, because human enzymes cannot digest it. In the large intestine (colon), however, it is partly or completely broken down by gut microbes (bacteria).
Inclusion of Insoluble fiber, or dietary fiber in general, in our daily diet is recommended. Dietary fiber is known to help relieve constipation, prevent or reduce risks of incidence of various diseases such as diabetes, heart diseases etc.
Insoluble fiber food sources are exclusively plant (vegeterian) products. Wheat bran is one of the highest insoluble fiber food sources. The following list contains foods high and low in insoluble fiber content.
High Insoluble Fiber Food Sources
| Ranking | Insoluble Fiber Food Sources | Insoluble Fiber Content (g/100g food portion) |
|---|---|---|
| 1 | Wheat bran | 36.3 |
| 2 | Linseed (flax seed) | 27.2 |
| 3 | Cocoa powder | 22.8 |
| 4 | Oat bran | 16.7 |
| 5 | Carrot, dried | 13.8 |
| 6 | Bean brown/white | 13.5 |
| 7 | Coconut flake | 13.3 |
| 8 | Crispbread, rye new | 12.8 |
| 9 | Crisp rye bread | 12.7 |
| 10 | Wheat germ | 12.7 |
| 11 | Bran flakes | 11.6 |
| 12 | Malt for beer | 11.5 |
| 13 | Rye malt | 11.5 |
| 14 | Rye flakes | 11.4 |
| 15 | Rye flour whole meal | 11.4 |
| 16 | Rye bran | 11.4 |
| 17 | Rye grain, crushed | 11.4 |
| 18 | Dried ryebread | 10.9 |
| 19 | Rye flour light refined | 10.8 |
| 20 | Pea, dried | 10.0 |
| 21 | Wheat grain, crushed | 9.5 |
| 22 | Rose hip puree without sugar | 9.5 |
| 23 | Soya beans | 9.3 |
| 24 | Weetabix wheat biscuit | 9.3 |
| 25 | Wheat flakes | 8.9 |
| 26 | Wheat flour whole grain | 8.9 |
| 27 | Ryebread | 8.5 |
| 28 | Maize, kernel, dried | 8.4 |
| 29 | Powdered mixture of dried oats and barley | 8.3 |
| 30 | Rye bread with whole grains and potato | 8.2 |
| 31 | Mixture of flakes | 7.9 |
| 32 | Soy meal, white | 7.8 |
| 33 | Soya flour low-fat | 7.8 |
| 34 | Peanut | 7.7 |
| 35 | Peanut salted | 7.5 |
| 36 | Crispbread, wholemeal | 7.3 |
| 37 | Rose hip | 7.3 |
| 38 | Banana weetabix, wheat biscuit | 7.3 |
| 39 | Popcorn | 7.2 |
| 40 | Popcorn industrial fat | 7.2 |
| 41 | Rye mixed grain bread | 7.1 |
| 42 | Exotic fruit average, mango, papaya, dried | 7.1 |
| 43 | Peach dried | 7.1 |
| 44 | Mixed rye and wheat flour | 7.0 |
| 45 | Ryebread | 6.9 |
| 46 | Ryebread low-sodium, with grains | 6.9 |
| 47 | Almond | 6.9 |
| 48 | Lentils green/brown | 6.9 |
| 49 | Bean stew dried beans | 6.8 |
| 50 | Barley flour | 6.6 |