Dietary fiber
Dietary fiber (fibre in Commonwealth English) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes.
[2][3] A diet high in regular fiber consumption is generally associated with supporting health and lowering the risk of several diseases.
[6] Bulking fibers – such as cellulose and hemicellulose (including psyllium) – absorb and hold water, promoting bowel movement regularity.
[7] Fermentable fibers – such as resistant starch, xanthan gum, and inulin – feed the bacteria and microbiota of the large intestine and are metabolized to yield short-chain fatty acids, which have diverse roles in gastrointestinal health.
[2] Inulin (in chicory root), wheat dextrin, oligosaccharides, and resistant starches[11] (in legumes and bananas) are soluble non-viscous fibers.
[2] Regular intake of soluble fibers such as beta-glucans from oats or barley has been established to lower blood levels of LDL cholesterol.
[20] Medical authorities, such as the Mayo Clinic, recommend adding fiber-rich products to the Standard American Diet because it is rich in processed and artificially sweetened foods, with minimal intake of vegetables and legumes.
These may be marketed to consumers for nutritional purposes, treatment of various gastrointestinal disorders, and for such possible health benefits as lowering cholesterol levels, reducing the risk of colon cancer, and losing weight.
Soluble fiber supplements may be beneficial for alleviating symptoms of irritable bowel syndrome, such as diarrhea or constipation and abdominal discomfort.
[35] One insoluble fiber, resistant starch from high-amylose corn, has been used as a supplement and may contribute to improving insulin sensitivity and glycemic management[36][37][38] as well as promoting regularity[39] and possibly relief of diarrhea.
Inulin is typically extracted by manufacturers from enriched plant sources such as chicory roots or Jerusalem artichokes for use in prepared foods.
[44] Subtly sweet, it can be used to replace sugar, fat, and flour, is often used to improve the flow and mixing qualities of powdered nutritional supplements, and has potential health value as a prebiotic fermentable fiber.
[45] As a prebiotic fermentable fiber, inulin is metabolized by gut flora to yield short-chain fatty acids (see below), which increase absorption of calcium,[46] magnesium,[47] and iron.
[48] The primary disadvantage of inulin is its fermentation within the intestinal tract, possibly causing flatulence and digestive distress at doses higher than 15 grams/day in most people.
Many molecules that are considered to be "dietary fiber" are so because humans lack the necessary enzymes to split the glycosidic bond and they reach the large intestine.
[53] Fermentable fibers are consumed by the microbiota within the large intestines, mildly increasing fecal bulk and producing short-chain fatty acids as byproducts with wide-ranging physiological activities.
This fermentation influences the expression of many genes within the large intestine,[54] which affect digestive function and lipid and glucose metabolism, as well as the immune system, inflammation and more.
Most semi-solid foods, fiber and fat are a combination of gel matrices which are hydrated or collapsed with microstructural elements, globules, solutions or encapsulating walls.
[70] Two mechanisms bring nutrients into contact with the epithelium: The multiple physical phases in the intestinal tract slow the rate of absorption compared to that of the suspension solvent alone.
The reduction in absorption rate with guar gum may be due to the increased resistance by viscous solutions to the convective flows created by intestinal contractions.
Some non-absorbed carbohydrates, e.g. pectin, gum arabic, oligosaccharides and resistant starch, are fermented to short-chain fatty acids (chiefly acetic, propionic and n-butyric), and carbon dioxide, hydrogen and methane.
Water is distributed in the colon in three ways: Fecal weight is dictated by: Preliminary research indicates that fiber may affect health by different mechanisms.
[83][84][85] As of 2019, preliminary clinical research on the potential health effects of a regular high-fiber diet included studies on the risk of several cancers, cardiovascular diseases, and type II diabetes.
Certain bulking agents are not commonly recommended with the prescription of opioids because the slow transit time mixed with larger stools may lead to severe constipation, pain, or obstruction.
In the preferred food choices of today's youth, this value may be as low as 20%, a factor considered by experts as contributing to the obesity levels seen in many developed countries.
[103] In 2018, the British Nutrition Foundation issued a statement to define dietary fiber more concisely and list the potential health benefits established to date, while increasing its recommended daily minimum intake to 30 grams for healthy adults.
These components include resistant starches and oligosaccharides along with other substances that exist within the plant cell structure and contribute to the material that passes through the digestive tract.
Overall, SCFAs affect major regulatory systems, such as blood glucose and lipid levels, the colonic environment, and intestinal immune functions.
As discussed in FDA regulation 21 CFR 101.81, the daily dietary intake levels of soluble fiber from sources listed above associated with reduced risk of coronary heart disease are: Soluble fiber from consuming grains is included in other allowed health claims for lowering risk of some types of cancer and heart disease by consuming fruit and vegetables (21 CFR 101.76, 101.77, and 101.78).
[12] In December 2016, the FDA approved a qualified health claim that consuming resistant starch from high-amylose corn may reduce the risk of type 2 diabetes due to its effect of increasing insulin sensitivity.
