Fiber - Skildum Flashcards
What does fiber refer to?
carbohydrates that are not digestible
What four things does fiber affect?
- GI motility
- absorption of nutrients
- the GI microbiome
- immunity
If present in a polymer of glucose, which of the bonds below is not a substrate for human carbohydrate digestive enzymes?
- A. alpha- 1,4
- B. alpha-1,6
- C. beta-1,4
- D. alpha-1,1
C. beta-1,4.
Lactose has a beta-1,4 bond, but it is a glucose / galactose disaccharide, not a glucose polymer.
- Alpha 1,4: amylase, glucoamylase
- Alpha 1,6: sucrase – isomaltase complex
- beta-1,4: lactase
- alpha 1,1: trehalase
Indigestible fiber can be converted to _______ by bacteria in the lumen of the gut.
- A. glucose
- B. alanine
- C. acetate
- D. hydrochloric acid
- E. phenol
C. acetate
What component of human breast mild can be converted to short chain fatty acis in the gut of a healthy infant?
- A. Triglycerides
- B. Phospholipids
- C. Protein
- D. Oligosaccharides
- E. Lactose
A. Oligosaccharides
Which cytokine acts as a brake on inflammation?
- A. TNF-alpha
- B. IL-2
- C. IL-10
- D. G-CSF
- E. IL-6
C. IL-10
How is fiber classified?
- Fiber is classified as either soluble or insoluble.
- Insoluble fibers are non-viscous
- Soluble fiber can be viscous or non-viscous
What type of insoluble fiber is a major component of plant cell walls? It is abundant in bran, beans, nuts, root vegetables and apples.
Cellulose
What insoluble fiber has branched polymers of phenolic subunits? It found in the stems and seeds of fruits.
Lignin
What insoluble fiber is a branched polymer abundant in bran, whole grains, and nuts?
(With acidic side chains it can be soluble.)
Hemicellulose
What soluble fiber is made up of branched polymers abundant in apples, strawberries and apples? It is almost completely degraded by gut bacteria.
Pectin
What soluble fiber is secreted by plants to close wounds. They are common food additives, and are completely fermented by gut bacteria.
Gums, a.k.a. hydrocolloids
What soluble fiber is found in oats, barley and mushrooms. They are fermented by gut bacteria to short chain fatty acids.
Beta-glucan
What soluble is found in asparagus, leeks, onions, garlic, tomato and banana? They are prebiotics, promoting the growth of bifidobacteria (gram positive anaerobes) in the gut.
Fructans, a.k.a. polyfructose
What soluble fiber has a structure similar to gums? It is quite indigestible, holds a lot of water, and is found in many grains.
Psyllium, a.k.a. mucilage
(in Metamucil)
What two insoluble fibers are found in the exoskeletons of insects and crustaceans? Their structure is similar to cellulose, but with amino group substitutions on the glucoses.
Chitin and chitosan
What are four types of resistant starch that are inaccessible by amylose and amylopectin?
- plant cell walls
- starch granules within cells
- retrograde starch (cooked then cooled)
- chemically crosslinked starch
What polymer of glucose and sorbitol is used as a food additive to replace sugar? It is soluble, and partially fermented by the gut.
Polydextrose
What effects do soluble fibers have on GI functions?
- delays gastric emptying
- increases transit time through the GI
- decreases nutrient uptake
What effects do insoluble fibers have on GI functions?
- decreases intestinal transit time
- increases fecal bulk
What effects do viscous fibers have on GI functions?
- delay gastric emptying
- decrease mixing of food with digestive enzymes
- decrease nutrient diffusion
- increases small intestine transit time
What are the beneficial effects of a diet high in fiber?
- Decreased lipid absorption
- Fiber prevents micelle formation required for fat uptake.
- Lowered serum cholesterol concentrations
- Increased excretion (and reduced uptake) of bile acids
- Gut microbiome
- Fiber promotes the growth of lactobacilli and bifidobacteria
- Fiber is used by bacteria to generate short chain fatty acids
- Increased fecal bulk
- Decreased intraluminal pressure decreases diverticulitis
Through interacting with which receptor do short-chain fatty acids inhibit inflammation?
GPR43
Short chain fatty acids (SCFA) produced by fermentation of dietary fiber affect immune cells by acting as a ligand for GPR43, and by inhibiting histone deacetylases (HDAC).
What effect does activation of GPR43 have in adipocytes?
Activation by short chain fatty acids inhibits insulin dependent storage of fatty acids, increasing their use by other tissues.
What diet is best for infants?
- A. Cow milk + formula
- B Raw cow milk
- C. Breast milk
- D. Soy based formula
- E. RC Cola
C. Breast milk
(“Breast is best!”)
Which dietary fiber decreases intestinal transit time?
- glucan
- lignin
- pectin
- psyllium
- fructan
Lignin
(Lignin is insoluble; all the others are soluble.)
