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Fiber

Fiber

Why is Fiber Important?

Fiber Definitions and Concepts1:

Dietary Fiber: refers to the nondigestible (by human digestive enzymes) carbohydrates and lignin (a complex organic polymer deposited in the cell walls of many plants, making them rigid and woody) that are intact and intrinsic in plants.

Functional Fiber: consists of isolated, extracted, or manufactured nondigestible carbohydrates that have been shown to have beneficial physiological effects in humans.  They are typically added to foods and supplements.  All dietary fibers are functional fibers except for hemicellulose, fructans, and lignin.  Psyllium (a mucilage) is considered a functional fiber.  Chitin and chitosan (ground shellfish shells), as well as polydextrose & polyols (sugar alcohols used as artificial sweeteners and supplemental fiber) require additional studies to determine if can be considered functional fibers.

Total Fiber: dietary fiber present in food and functional fiber added to food combined.

  • Beta-Glucans: water soluble, highly fermentable by colonic bacteria, and form viscous gels within the digestive tract.  Found in oats, barley, reishi, maitake and shiitake mushrooms, seaweed, algae, and nutritional yeast.  Effective in lowering serum cholesterol and moderating blood glucose concentrations.  Added to foods as a functional fiber due to health promoting benefits.  FDA allows health claims of beta-glucans in lowering LDL cholesterol resulting from the intake of greater than or equal to 3 grams of oats daily (3/4 cup of rolled oats is 67.5 grams).

Viscous Gel-forming Fiber:  ability to both bind or hold water and form a gel.  Think of fiber as a dry sponge that hydrates or soaks up water and digestive juices as it moves through the digestive tract.  Fibers that are viscous gel forming are pectins, beta-glucans, mucilages (psyllium), and gums.

Health benefits from ingesting viscous gel-forming fiber:

  • Delayed gastric emptying and longer intestinal transit time increasing satiety
  • Trap nutrients, especially sugar (glucose) and fats (lipids) and interferes with their ability to interact with digestive enzymes. Meaning, they will trap sugar and fat and bring it through the digestive system.
  • Decreased convective movement of nutrients especially amino acids (broken down proteins) and fatty acids (broken down fats). Helps nutrients absorb better in the small intestine.
  • Traps sugar and cholesterol to reduce the absorption of both into the blood stream.

Soluble Fiber:  Fiber that dissolved in hot water.  Foods rich in soluble fiber are legumes, oats, barley, rye, chia, flaxseed, most fruits (especially berries, bananas, apples, pears, plums, and prunes), some vegetables (carrots, broccoli, artichokes, and onions), and cooked pasta, rice, and potatoes. This type of fiber is known to delay gastric emptying, increase intestinal transit time (slower movement through GI tract), and decrease nutrient absorption.  These effects positively impact blood glucose and lipid concentrations.

Insoluble Fiber: Fiber that does not dissolve in hot water.  Insoluble fibers are thought to decrease (speed up) intestinal transit time and increase fecal weight to positively impact the elimination of fecal waste.

Gums: are secreted at the site of plant injury by specialized secretory cells and can be exuded from plants (forced out by plant tissues) or made from the ground endosperm of guar gum and locust bean seeds.  Used as a thickening agent and water binding agent in products such as baked goods, sauces, dairy products, ice creams, dips, and salad dressings.  Gums are also found naturally in foods such as oatmeal, barley, and legumes.  They dietary and functional fibers, water-soluble, digested by colonic bacteria, and can form viscous gels.

Pectin:  is a dietary and functional fiber found in plant cell walls.  Foods rich in pectins are apples, berries, apricots, cherries, grapes, citrus fruits, legumes, nuts, and some vegetables.  Think any plant that you eat the skin.  They are water soluble, form viscous gels, and are almost completely digested by colonic bacteria.

Resistant Starch:  is starch that cannot be or is not easily enzymatically digested.  There are 4 main types.

  1. RS1 – is starch physically inaccessible to digestion due to its location in a plant’s structure. Examples are whole or partially milled grains and seeds. Dietary fiber.
  2. RS2—is starch that resists digestion because it is tightly packaged inside granules within foods. Examples are green/unripe bananas, some legumes, and potatoes.  Heating these foods gelatinizes the starch and increases their ability to be digested.  Dietary fiber.
  3. RS3—Retrograde starch or amylose. It is formed with moist heat cooking and then cooling of starch that has gelatinized.  Examples are cooked and cooled potatoes, rice, pasta, bread, and some corn. Functional fiber.
  4. RS4—results from chemical modifications of starch (usually from corn).

Both RS3 and RS4 may be partially digested by colonic bacteria and may stimulate the growth of healthful bacteria and may improve the glycemic response following carbohydrate ingestion.  It is thought that American intake ~10 grams resistant starch/day.  It is recommended to intake ~20 grams/day to obtain health benefits.

Mucilage:  are plant polysaccharides with a structure like gums.  Mucilages are found in seeds like flaxseed and psyllium.  They have high water-binding capacity and form viscous gels in the digestive tract.  The FDA permits health claim for psyllium with consumption of 10.2 grams (providing 7 grams of viscous fiber) resulting significant reductions in LDL cholesterol.  Psyllium must be eaten with a full glass of liquid to avoid choking.

Hemicellulose: Dietary fiber that is both water soluble and water insoluble.  Colonic bacteria can ferment some hemicelluloses.  Foods that are relatively high in hemicellulose fiber are whole grains, nuts, legumes, and some fruits and vegetables.

Fructans: fiber found in chicory, asparagus, leeks, onions, garlic, Jerusalem artichokes, tomatoes, and bananas.  Wheat, barley, and rye contain some fructans.  Fructans are sometimes added to foods such as cereals, fruit preparations for yogurt, dairy products, dressings, frozen desserts, and sometimes in gummy supplements.

Lignin: provides structural support in plant cell walls.  It is found in the bran layer of cereals and in the stems and seeds of fruits and vegetables.  Lignin is a dietary fiber and is insoluble in water.  It is not digested by colon bacteria.  It is found in wheat, rye, mature root vegetables, flaxseed, and fruit with edible seeds.

Chitin & Chitosan: ground up shells of crabs, shrimp, and lobsters.

“Complete Protein”:  Usually referring to a protein having all 9 essential amino acids

  • Phenylalanine
  • Valine
  • Threonine
  • Methionine
  • Tryptophan
  • Histidine
  • Isoleucine
  • Leucine
  • Lysine

Essential Amino Acids:  those amino acids that are required to be ingested and the body cannot produce on its own.  In a normally functioning body, it can assemble all essential amino acids from various food ingested.  To get all essential amino acids it does not have to be in one food source.

Polydextrose/Polyols:  a synthetic polymer of glucose.  It is a food ingredient classified by the F.D.A. as soluble fiber.  It is used to increase the dietary fiber content of food, to replace sugar, and reduce calories.

References:

  1. Gropper SS, Smith JL, Carr TP. Advanced Nutrition and Human Metabolism. Seventh Edition. Boston, MA: Cengage Learning; 2018.
  2. National Fiber Council. How Fiber Works. https://nationalfibercouncil.org/. Accessed September 29, 2021.
  3. Dr. Justin Sonnenburg Dept. Microbiology & Immunology Stanford University. Your Microbiome: What is it and how can it help you or hurt you? https://www.youtube.com/watch?v=EAvL0md46_M. May 30, 2017. Accessed September 29,2021.
  4. Dr. Michael Greger. How Fiber Lowers Cholesterol. NutritionFacts.org. https://www.youtube.com/watch?v=isqfylnln_Y . August 13, 2012. Accessed September 29, 2021.
  5. United States Department of Agriculture. Fiber. https://www.nutrition.gov/topics/whats-food/fiber . Accessed September 29, 2021.
  6. Mayo Clinic. Top 5 Lifestyle Changes to Improve Your Cholesterol. https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/in-depth/reduce-cholesterol/art-20045935. Published date August 28, 2020. Access date September 29, 2021.
  7. Zhang P, Yang C, Guo H, Wang J, Lin S, Li H, Yang Y, Ling W. Treatment of coenzyme Q10 for 24 weeks improves lipid and glycemic profile in dyslipidemic individuals. Clin Lipidol. 2018; 12 (2): 417-427.
  8. Better Health Channel. Victoria State Government Department of Health. Victoria, Australia. https://www.betterhealth.vic.gov.au/health/healthyliving/antioxidants. Updated June 6, 2020.  Accessed September 29, 2021.