GRQ #4 Fiber

There is no gold standard for testing the fermentability of a fiber. Why? What are 2 reasons?

This would require anaerobic conditions, making it really difficult to study. There are other variables involved- the make up of the gut bacteria, which may differ greatly from person to person, so it is difficult to predict the amount of fermentation that would occur in each individual, even if the fiber is 'fermentable'.

Name 2 or 3 examples of functional fibers that are used in food products sold today? What products are they?

Cellulose is added to products such as breads, sauces, dips, frozen chicken nugget. Pectins are added to fruit strips, fruit juices, and enteral nutrition products. Psyllium is added to Metamucil for its laxative properties

Name 5 - 10 types of fiber and classify them as dietary or functional. Could a fiber be both? Give examples

Cellulose- dietary fiber and functional fiber (added to foods as a texturizing agent) Hemicellulose- dietary fiber Lignin-dietary fiber and functional fiber Inulin- dietary fiber Psyllium- functional fiber Yes- a fiber could be both. Cellulose is a dietary fiber and a functional fiber. Pectins are both dietary and functional fiber. Gums are both dietary and functional fiber. Beta glucans are also both dietary and functional fiber.

What is definition of fiber? What is the difference between dietary and functional fiber?

Dietary fibers refers to nondigestible (by human digestive enzymes) carbohydrates and lignin that are intact and intrinsic in plants. They include cellulose, hemicellulose, pectins, lignin, gums, beta-glucans, fructans, and resistant starches. Functional fiber is defined as isolated, extracted, or manufactured nondigestible carbohydrates that have been shown to have beneficial physiological effects in humans (they are usually added to foods as well as found in supplements). The difference is that dietary fibers are inherent in foods; functional fibers are isolated and added to foods. Total fiber refers to the dietary fiber naturally present in a food plus any functional fiber added to the food.

"Ingesting foods rich in these gel-forming fibers is associated with...[health benefits]". These generalizations are very broad. What factors could influence these statements?

Factors that could influence the health association of intake of gel forming fibers include other foods that the individual consumes, whether the individual is at risk for high cholesterol or high triglycerides, whether in a certain individual the fibers form a gel in the GI tract, and comorbidities, among others.

What does fermentation mean? And, what are two benefits of fermented fibers?

Fermentation is a metabolic process by which bacteria enzymatically digest carbohydrates in the absence of oxygen. The byproducts are short chain fatty acids, CO2, and alcohol. -Two benefits of fermented fibers are: a) production of SCFA, which feed colonocytes and may positively impact appetite regulation b) potential prebiotic function, stimulating growth and activity of intestinal bacteria.

The impact of fiber on health is really (really) difficult to study in humans. Why? Hints: a. Think about the definition of fiber. b. Think about the foods fiber is in.

Fiber is difficult to study in humans because the health impact relates to gut bacteria and our individual physiology which differs from person to person. In addition, the fiber content of each food item varies (even within the same foods). The foods that fiber is present in are often perishable and nutrients (including fiber) degrade over time. Lastly, unless it is an tightly controlled experimental study in which subjects are provided the foods, are observed, and exact consumption is determined, it is hard to know how much fiber people consume.

Why are fibers indigestible to us? Draw a fiber molecule and a glucose molecule (see pg. 66 for glucose figure and pg 68 for refresher on polysaccharide digestion).

Humans do not have the enzymes needed to cleave the bonds in fiber molecules for digestion. For example, in cellulose (found in whole grains, bran, legumes, peas, and nuts), glucose units are linked together by 1-4 bonds. We do not make an enzyme that cleaves these 1-4 bonds, thus leaving cellulose intact through the GI tract. - Polysaccharides and (some) fibers look very similar in that they are both chains of glucose. The difference is the bonds between the molecules of glucose, and whether or not we have the enzyme to cleave those bonds.

Describe how fiber may relate to health impact? Is fiber really clear cut like the figure? (Hint: think about the different properties of fiber)

Increased intake of gel forming fibers may result in favorable glycemic responses and reduced serum cholesterol and triglycerides. Increased intake of non/less fermentable fibers improves laxation. Increased intake of fermentable fibers may increase fecal mass and increase SCFA production (positive health impact).Solubility has turned out to not be a great way to classify fiber in terms of impact on health, since impact is not consistent based on solubility.

What are the general properties of insoluble fibers?

Insoluble fibers may add bulk to fecal weight and improve laxation

Describe 3 ways SCFA production may benefit health.

SCFA may benefit health by providing an energy source for colonocytes, by regulating appetite signaling, and by increasing water and sodium absorption. They may also inhibit tumors, and stimulate the immune system.

What are the general properties of soluble fibers?

Soluble fibers may delay gastric emptying, increase intestinal transit time, and decrease nutrient absorption to positively impact blood glucose and lipid concentrations

What is a prebiotic? Define it and give examples of food you (or someone you know) eats. Include some examples of dietary fiber and some that are functional fiber.

To be classified as a prebiotic, 3 criteria must be met: 1) it must resist digestion by human enzymes and absorption 2) the ingredient must serve as a substrate for fermentation by intestinal microorganisms in the human microbiota 3) it must selectively stimulate the growth and/or activity of health-promoting intestinal bacteria. Fibers meeting the criteria for prebiotics include fructans, lactulose, and galactooligosaccharides. Inulin and oligofructose are dietary fibers; fructooligosaccharides are functional fiber (these 3 are under the category of fructans). Inulin is in asparagus, leeks, onions. Oligofructose is in cereals, dairy products, and frozen desserts.

What are the three ways that fibers are often classified (described)? Describe each classification.

a. Solubility- (whether they dissolve in hot water or not) -it used to be thought that soluble fibers delayed gastric emptying and positively impact blood glucose and lipid concentrations. Insoluble fibers were thought to increase fecal weight and improve laxation. But this classification as an indicator of impact on health has not proven consistent over time and thus is not relied upon as much anymore. b. Viscosity- (whether the fiber binds water or not) Some fibers form a gel in the GI tract. Those that do form a viscous gel in the GI tract are associated with health benefits and include pectins, beta glucans, psyllium, gums. The associations include delayed gastric emptying and increased satiety, reduced lipid digestion, reduced bile recirculation, reduced cholesterol absorption. c. Fermentability- (whether the fiber is fermented by colonic bacteria)- Those that are not fermentable promote laxation by increasing stool bulk. Those that are fermentable provide a source of short chain fatty acids, and energy for the colonic cells and for the host.