1. Discuss the four significant characteristics of dietary fiber that affect its physiological and metabolic roles.     
 Solubility/insolubility in water. Pectins, gums, beta-glucans, fructans, psyllium, some resistant starches, and some hemicelluloses are soluble. Cellulose, lignin, some heicelluloses and pectins, some resistant starches, chitosan, and chitin are insoluble. In general, soluble fibers delay gastric emptying and slow down transit time through the GI tract and slow glucose entry into the blood. Insoluble fibers increase fecal bulk and speed up transit time, which may expose the colon to fewer toxins. Water-holding/hydration capacity and viscosity. Soluble fibers have greater water-holding capacity, which traps nutrients and slows absorption, than insoluble fibers. Characteristics other than solubility that affect water-holding capacity are pH of the GI tract and particle size of the fiber (coarsely ground has more holding capacity). The more coarsely ground whole grains hold more water, slow gastric emptying, and reduce enzyme functions by separating enzymes from substrates. Adsorption or binding ability. Lignin, gums, pectins, betaglucans, and a few other fibers attach to substances such as enzymes and nutrients and keep them from being absorbed. This is important for increasing fecal bile acid excretion, which helps lower blood cholesterol. This characteristic can also negatively affect the ability of some minerals and phytochemicals such as carotenes to be absorbed into the enterocytes and eventually into the blood for use. Degradability/fermentability. Fiber always reaches the colon undigested because it cannot be digested by human enzymes. Gut bacteria can digest (i.e., ferment) some fibers. This helps gut bacteria grow and prebiotic fibers in particular support the growth of nonpathogenic, acid-producing bacteria that improve gut health. Some products of fermentation of fibers are the shortchain fatty acids that can improve health of colon cells and may inhibit synthesis of cholesterol to lower blood cholesterol levels. Short-chain fatty acids may also enhance gut immune function. Poorly-fermentable fibers such as cellulose and lignin increase fecal bulk and speed transit time to promote more frequent defecation and quicker removal of toxins that might harm colon cells. 2. Consistent evidence shows that soluble fibers can lower the levels of cholesterol in many people with high serum cholesterol. Discuss the three mechanisms by which fibers are proposed to lower serum cholesterol. 
 First. Cholesterol and bile acids adhere to the soluble fibers and are removed as waste rather than recirculated to the liver. This forces the liver to make new bile acids from cholesterol, increases uptake of LDL cholesterol from the blood, and thereby lowers blood cholesterol. Second. Microbial fermentation of fermentable soluble fibers produces shortchain fatty acids. Propionic acid has been shown to inhibit the rate-limiting enzyme in the synthesis of cholesterol (HMG-CoA reductase) by the liver. When synthesis is slowed, less cholesterol enters the blood. Third. For reasons unknown, the shift by fiber-inhibition of recirculation of bile acids to creating additional new bile acids promotes increased chenodeoxycholic acid formation. This bile acid also inhibits HMG-CoA reductase and lowers synthesis of cholesterol. 3. What are the components that make up fermentable dietary fiber and in what foods are each found? 
 Fermentable fibers must be able to be digested (fermented) by gut bacteria. Examples of fermentable fibers and foods that contain them include:  fructans (chicory, asparagus, onions, tomatoes, bananas; also added to yogurts, cereals)  pectins (fruits, legumes, nuts)  gums (guar gum, gum Arabic; added as food additives that thicken)  beta-glucans (oats, barley, mushrooms)  polydextrose (created from glucose; used as a food additive for bulk; a functional fiber)  resistant dextrins (extracted from cooked and cooled wheat to be added to foods; considered a functional fiber rather than a natural fiber)  resistant starch 3 (cooked and cooled rice, potatoes, pasta)  4. Discuss the benefits of fermentable fibers in terms of their prebiotic function. 
 Certain fermentable fibers promote the growth of beneficial gut bacteria, particularly lactobacilli and bifidobacteria, because they are preferred food for growth of those bacteria. This extra growth in numbers of the beneficial bacteria promotes gut health because the beneficial bacteria can crowd out pathogenic bacteria and lower their numbers. 5. Discuss the benefits of fermentable fibers in terms of the production of shortchain fatty 
 acids. 
 Fermentable fibers are used by gut bacteria to produce lactic acid and shortchain fatty acids that have several benefits. All these acids decrease the pH to a more acidic environment, reducing the solubility of bile acids and allowing calcium to bind them and make them less toxic to colon cells. The acidity also decreases growth of pathogenic bacteria. Short-chain fatty acids can be absorbed and used for energy. Butyric acid is a preferred food for colonic mucosal cells (supplying 67% of their energy) and likely keeps them healthy, perhaps preventing colon cancer. Propionic acid, when absorbed, can inhibit cholesterol synthesis, lowering blood cholesterol and risk for heart disease. 6. What are the components that make up non-fermentable dietary fiber and in what foods 
 are each found? 
 Non-fermentable fibers cannot readily be digested (fermented) by gut bacteria. Examples and the foods that contain this type of fiber include:  Cellulose (cereal brans, legumes, nuts, root vegetables)  Lignin (whole grains, especially wheat; mature root vegetables; seeds of berries; stalks of broccoli and asparagus)  Waxes (suberin and cutin, which coat the external surfaces of apples, potatoes, and similar fruits and vegetables) 7. What associations have been found between high fiber intake and obesity? What 
 mechanisms may be at work? How clear/consistent is the evidence? 
 Fairly consistent evidence supports the consumption of a high-fiber diet for weight control. Possible mechanisms include more bulk causing a full feeling, less calories provided because of the undigestibility of fiber, and reduction of hunger through satietyinducing hormones.
Purchase answer to see full attachment