Dietary fiber consists of the components of plant cell walls and the indigestible parts. Cell walls are made up of 35% cellulose (insoluble fiber), 45% non-cellulose polysaccharides (soluble fiber), 17% lignins, 3% protein, and 2% ash., . A combination of all components of fiber is essential and substituting with a single part will not provide adequate and optimal fiber intake, although certain conditions may warrant one over the other.
Insoluble fiber is insoluble in water but it can bind to water. This characteristic allows it to increase stool size and weight and promotes bowel movements. Soluble fiber includes hemicelluloses, mucilages, gums, and pectin substances. Hemicelluloses for example, promote bowel movement, provide short-chain fatty acids, and also lowers cholesterol levels.
There are many benefits to eating a diet high in fiber. First, dietary fiber, particularly cellulose, increases stool weight and reduces transit time. An increase in transit time leads to prolonged exposure to various cancer-causing compounds in the intestines and thus decreasing transit time is desirable in most cases. Moreover, fiber is used to regulate bowel movement and can increase transit time in the case of chronic diarrhea. Second, dietary fiber slows gastric emptying which allows for gradual release of food into the small intestine. This results in a more gradual rise in blood glucose. Pancreatic enzyme activity also increases. Third, water-soluble fibers decrease cholesterol and triglyceride levels by increasing their excretion in the feces. Fourth, fermentation of fiber in the gut results in short-chain fatty acids such as butyrate which provides fuel to the cells of the colon. This may lead to anticancer activity. Not all fiber is fermentable. Fifth, fiber is also important for maintaining proper bacterial flora in the colon 
The typical Western diet is notorious for being low in dietary fiber. This has lead to higher incidences in metabolic diseases such as diabetes, obesity, cardiovascular diseases, and colonic diseases such as colon cancer, irritable bowel syndrome and inflammatory bowel disease.
The following foods have the highest concentration of dietary fiber. For a more expansive list on food sources of specific nutrients visit Health Canada's Dietary Reference Intakes for Macronutrients or USDA's National Nutrient Database
- baked beans, all bran, kidney beans, navy beans, parsnips, broccoli, brussel sprouts, carrots, lima beans, lentils, whole wheat spaghetti, apple (with the skin)
- Irritable Bowel Syndrome (IBS): The best form of fiber with which to supplement in the case of IBS is water-soluble. Nonetheless, many studies testing the benefit of fiber in this condition use wheat bran which is an insoluble fiber. Furthermore, wheat is also a common food allergen implicated in the pathophysiology of IBS, making the condition worse at times, especially for those who suffer more from diarrhea.
- Elevated Cholesterol Levels: Soluble fiber has also shown a significant total cholesterol lowering effect in individuals with elevated cholesterol but little change in those with normal or low cholesterol. The studies used either oat bran or oatmeal. In patients with high cholesterol, the equivalent of 3 grams of soluble oat fiber lowered total cholesterol by 8-23%. This is a considerable effect considering that every 1% decrease in serum cholesterol equates to a 2% decrease in one's risk of developing heart disease 
Oatmeal also contains polyunsaturated fatty acids which also contribute to its cholesterol lowering effects.
- Obesity: Water-soluble fiber taken with water before meals aids in making an individual feel full. This decreases the likelihood that he or she will overeat. Furthermore, fiber enhances blood sugar control and insulin effects and even reduces the number of calories that are absorbed. Weight-loss studies using guar gum have shown extremely positive results.
- Cancer Prevention: Most but not all studies have been able to show the protective effect of dietary fiber for a variety of cancers. Several studies have shown its protective effects in breast cancer. These protective effects are also seen in individuals with fibrocystic breast disease. Other studies have shown its benefit in patients who have had colon cancer.
The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- Child: 19g/day (1-3 years); 25g/day (4-8 years)
- Adolescent: 31g/day (boys 9-13 years); 38g/day (14-18 years); 26g/day (girls 9-18 years)
- Adult: 38g/day (Males 19-50 years); 30g/day (Males >51 years); 25g/day (Females 19-50 years); 21g/day (Female >51 years)
- Pregnancy: 28g/day
A diet low in plant food intake and dietary fiber results in the development of many chronic degenerative diseases. The following is a list of now common degenerative diseases linked to low plant food intake and dietary fiber which we extremely rare before the twentieth century :
- Metabolic: obesity, gout, diabetes, kidney stones, gallstones
- Cardiovascular: heart disease, high blood pressure, stroke, varicose veins, deep vein thrombosis, pulmonary embolism
- Colonic: constipation, appendicitis, diverticulitis, diverticulosis, hemorrhoids, colon cancer, irritable bowel syndrome, ulcerative colitis, Crohn's disease
- Other: dental caries, autoimmune disorders, Pernicious Anemia, multiple sclerosis, thyrotoxicosis, various skin conditions
- Large amounts of supplementary fiber may inhibit the absorption of some minerals. Fiber as a dietary component does not appear to display this same interference.
- It is best to start with small doses and increase gradually. Water-soluble fibers are fermented by intestinal bacteria and therefore can produce considerable amounts of gas particularly for individuals not used to a high-fiber diet. This can produce abdominal bloating and flatulence. It is best to start with a dosage between 1-2g before meals and at bedtime and gradually increase to 5g 
The safety precautions for Dietary fiber include:
- disorders of the esophagus (fiber supplements may expand in the esophagus and lead to obstruction)
- Drug Interactions
- It is recommended to take fiber supplements away from other drugs as fiber may inhibit absorption of certain drugs.
- Murray Michael T (1996) Encyclopedia of Nutritional Supplements: The Essential Guide for Improving Your Health Naturally, Prima Publishing
- Pizzorno Joseph E, Murray Michael T (1999) Textbook of Natural Medicine, Elsevier