Soluble fiber and short-chain fatty acids

Plants contain soluble or insoluble fiber in their different parts, such as their skin, pulp, seeds, stems, leaves or roots. Nutrients which we derive from plant products are digested with the aid of gastric acids and enzymes in the stomach and upper intestinal tract. The nutrients which are freed there are absorbed through the small intestine into the bloodstream and then distributed throughout the entire body. Part of the food, such as soluble and insoluble fiber is not digested or absorbed into the small intestine. Fiber continues on into the large intestine where insoluble fiber absorbs water and soluble fiber gets dissolved in water. Soluble fiber is fermented fully or partially by the colonic bacterial microflora. The degree and the speed of disintegration of the fiber depend on its type and on the type of bacterial flora in the large intestine.1

Partially fermenting fiber:2

• cellulose (vegetables, bran)
• hemicellulose (wheat grain)
• legunin (woody plants)
• plant waxes
• resistant starch (corn, potatoes, cereals, legumes, bananas)

Well fermenting fiber:2

• beta-glucans (grain: oats, barley, rye)
• pectins (fruit, vegetables, legumes, beet root, potatoes)
• natural gum
• inulin (chickory, Jerusalem artichokes, onions, wheat)
• oligosaccharides (monosaccharides)
• resistant maltodextrins3

Short-chain fatty acids

The process of fiber fermentation produces gases and short-chain fatty acids. Scientific research shows that short-chain fatty acids (SCFA) have considerable health benefits. The main human SCFA are: butyric acid, propionic acid and acetic acid. Butyric acid is the main nutrient for the intestinal lining, propionic acid is utilised by the liver and acetic acid is absorbed into peripheral circulation and is metabolised by the peripheral tissues.

SCFA are involved in many physiological processes important for human health. Amongst other things they:4

• stabilise blood glucose levels aiding the release of insulin from the pancreas, glucose uptake by the liver and the breaking down of glycogen in the liver.
• stimulate the expression of glucose transporters genes in the intestinal lining, by regulating the glucose uptake.5
• provide energy for colonocytes (this is especially true in relation to butyric acid).
• limit the synthesising of cholesterol in the liver and decrease the level of concentration of LDL cholesterol and triglyceride in the blood reducing the risk of artheriosclerosis.
• decrease the pH of the colon which in turn prevents the formation of polyps of the lining, increases the absorption of minerals, minimises various rotting processes and the development of intestinal infections such as Clostridium, Staphylococcus, Listeria, Escherichia, Salmonella, Shigella.1
• stimulate the production of limphocytes Th, antibodies, leukocytes, cytokines and lymphae, all of which are important for the immune system.
• protect the colon lining against bacterial infections and irritations.

Comments:

References:

1. 1. Kozłowska L. (2010) Rola błonnika pokarmowego w utrzymaniu prawidłowej pracy jelit, Żywność dla zdrowia 13(8):23-27.
2. 2. Tungland BC, Meyer D (2002) Nondigestible oligo- and polysaccharides (dietary fiber): their physiology and role in human health and food, Comp Rev Food Sci Food Safety, 3:73-92.
3. 3. Institute of Medicine (2005) Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. National Academies Press, Washington, D.C. s. 347. ISBN 0-309-08525-X
4. 4. Wong JM, de Souza R, Kendall CW, Emam A, Jenkins DJ (2006) Colonic health: fermentation and short chain fatty acids. J Clin Gastroenterol. 40(3):235-43. PMID: 16633129
5. 5. Drozdowski LA, Dixon WT, McBurney MI, Thomson AB (2002) Short-chain fatty acids and total parenteral nutrition affect intestinal gene expression. JPEN J Parenter Enteral Nutr. 26(3):145-50. PMID: 12005453