Hypercholesterolemia, dietary fiber

Recent scientific studies have clearly established the nutritional role of dietary fiber in several health conditions (Jalili et al., 2000), such as hypercholesterolemia (Topping et al., 1990), diabetes (Chandalia et al., 2000) and bowel function. It is also effective in preventing urinary stones (Ohkawa et al., 1984). The Food and Nutrition Board (Institute of Medicine Report, 2001) recommended a daily allowance for fiber of 25-30 g, though it is not an essential nutrient. Rice bran fiber offers a good source of non-bloating dietary fiber and is marketed as RiceMucil by NutraStar Company in the USA. 

Bile salts secreted into the intestine are efficiently reabsorbed (greater than 95 percent) and reused. The mixture of primary and secondary bile acids and bile salts is absorbed primarily in the ileum. They are actively transported from the intestinal mucosal cells into the portal blood, and are efficiently removed by the liver parenchymal cells. [Note Bile acids are hydrophobic and require a carrier in the portal blood. Albumin carries them in a noncovalent complex, just as it transports fatty acids in blood (see p. 179).] The liver converts both primary and secondary bile acids into bile salts by conjugation with glycine or taurine, and secretes them into the bile. The continuous process of secretion of bile salts into the bile, their passage through the duodenum where some are converted to bile acids, and their subsequent return to the liver as a mixture of bile acids and salts is termed the enterohepatic circulation (see Figure 18.11). Between 15 and 30 g of bile salts are secreted from the liver into the duodenum each day, yet only about 0.5 g is lost daily in the feces. Approximately 0.5 g per day is synthesized from cholesterol in the liver to replace the lost bile acids. Bile acid sequestrants, such as cholestyramine,2 bind bile acids in the gut, prevent their reabsorption, and so promote their excretion. They are used in the treatment of hypercholesterolemia because the removal of bile acids relieves the inhibition on bile acid synthesis in the liver, thereby diverting additional cholesterol into that pathway. [Note Dietary fiber also binds bile acids and increases their excretion.]... 

Jensen, C.D., Haskell, W. and Whittam, J.H. 1997. Long-term effects of water-soluble dietary fiber in the management of hypercholesterolemia in healthy men and women, Am. J. Cardiol., 79(l) 34-37. 

Jenkins, D.J. Reynolds, D. Slavin, B. Leeds, A.E. Jenkins, A.L. Jepson, E.M. Dietary fiber and blood lipids Treatment of hypercholesterolemia with guar crisp bread. Am J Clin Nutr 1980, 33, 575-81. 

Kritchevsky, D. Dietary fiber and other dietary factors in hypercholesterolemia. Am J Clin Nutr 1977, 30, 979-84. 

Hypercholesterolemia is an important risk factor for cardiovascular disease. The hypocholester-olemic action of chitosan can be explained to be due to the decrease in cholesterol absorption and interference with bile acid absorption, a mechanism similar to those of dietary fiber constituents. Here, the cholesterol-lowering effects of chitin, chitosan, and their derivates are reported based on animal and clinical studies. 

Jenkins, D.J. et al., A dietary portfolio approach to cholesterol reduction combined effects of plant sterols, vegetable proteins, and viscous fibers in hypercholesterolemia. Metabolism, 51, 1596, 2002. 

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