Soluble, Viscous, Fermentable fiber is often recommended to those with high blood cholesterol for several reasons.
1. The liver makes cholesterol from bile salts. Bile Salts are like the detergent of the intestine- Soluble fiber grabs onto Bile Salts in the liver and blocks reabsorption of Bile Salts, helping to extract them to the colon. The extraction of bile salts signals the liver to extract more cholesterol from the blood ( LDL cholesterol) to make more bile salts ( because of the enterhepatic [enter= inside, hepatic= liver ] concentration imbalance). The extraction of cholesterol from the blood = lower blood cholesterol.
2 High blood glucose leads to a high insulin response. Insulin triggers acitivty of HMG CoA reductase, an enzyme which we require to make cholesterol from scratch. If we can lower blood glucose, lower the insulin response, inhibiting HMG CoA (and inhibiting fat synthesis)… we inhibit making cholesterol.
3. (Highly Fermentable ) Fiber produces SCFA (short chain fatty acids) when bacterial fermentation occurs. SCFA go to the liver and inhibit HMG CoA reductase …. inhibits cholesterol production
***SCFA ( acetate: absorbed and used as energy for colonic cells, proprionate absorbed by liver and inhibits HMG CoA, Butyrate inhibits colon cell proliferation (growth)… all these SCFA help reduce blood cholesterol ) ****
4. (Viscous) Fiber delays CHO (carbohydrate) absorption as do Lipids and Proteins, this delay results in lower insulin response, and as I said in #2 … lower insulin response–> lower B. cholesterol.
Examples of these include guar gum, pectin, oat bran, bean and bean products and psyllium ( weird one b/c is insol. more than sol.) oranges, brussel sprouts..
5. Bile salt concentration also shifts on its own. 2 bile salts: cholic acid and chenodeoxycholic acid, can both inhibit HMG Co A ( inhibiting cholesterol synthesis)
* Drugs like Zetia and Zocor inhibit HMG CoA—- which inhibits cholesterol production
via inhibiting HMG CoA… this has a double benefit because when cholesterol is not produced from scratch, the extraction of cholesterol in the blood (to balance the bile salt concentration ) is likely to occur more frequently- which is also reducing the blood cholesterol.
As I mentioned on earlier posts on fiber… viscous (referring to the thickening gel consistency) has its fullness effect in your stomach ( the upper GI) … hence that “fullness” feeling everyone talks about related to fiber. Fermentability refers to its capacity to be broken down by bacteria, when its broken down – short chain fatty acids are produce- which also does NOT contribute to “fecal bulk” . Fecal bulk contributes to dilution of the lower GI… and now we are at…
Insoluble, Nonfermentable, Nonviscous Fiber is better at treating/preventing constipation.
Insoluble fiber contributes to fecal bulk since it is NOT fermented (broken down)… Fecal bulk ( along with water) helps dilute the bulk = relieving constipation
So wheat bran, cellulose, lignin are all better sources for constipation reilief
Colon Cancer and Fiber
Fermentation increases the production of SCFA, but does not contribute to fecal bulk. Fecal bulk helps dilute the GI tract. Dilution of the GI including diluting compounds such as bile acids, diglycerides, ammonia…. These compounds STIMULATE cell division in the colon- which is BAD news since dividing cells makes cells more susceptible to carcinogens.
Poorly fermentable fiber helps dilute the GI- helping to protect against cancer