Fiber and colorectal diseases: Separating fact from fiction

Table 1 Classification of fiber

	Material	Chemical structure	Source	Hydrolysis	Fermentation in colon
Soluble fibers
	Pectins	Nonstarch polysaccharide	Plant cell wall	Yes	Rapid
	Guar	Nonstarch polysaccharide	Beans	Yes	Rapid
	Ispaghula	Acidic arabinoxylan	Husks of seeds of platago ovata	Yes	Rapid
	Hemicellulose	Nonstarch polysaccharide	Component of plants	Yes	Variable
Insoluble fibers
	Cellulose	Nonstarch polysaccharide	Component of plants	Minimal	Variable
	Hemicellulose	Nonstarch polysaccharide	Component of plants	Partial	Variable
	Lignin	Nonpolysaccharide cell wall component	Component of plants	Nearly none	Minimal
Resistant starch
	Starch not digested in small intestine	Polysaccharide	Legumes/ Grains	Minimal	Complete

Table 2 Case-control studies correlating dietary fiber with colorectal neoplasia

Reference	Country	Number of cases/controls	Odds ratio of CRC comparing highest to lowest fiber intake groups	Dietary fiber protective
Wakai et al 2006[15]	Japan	507/2535	0.65 (P < 0.05)	Yes (colon)
Levi et al 2001[16]	Switzerland	286/550	0.55 (P < 0.05)	Yes
Ghadirian et al 1997[17]	Canada	402/668	0.50 (P < 0.01)	Yes
Slattery et al 1997[18]	United States	1993/2410	0.70 (95% CI 0.5-1.0)	No
Little et al 1993[19]	United Kingdom	147/329	0.60 (not significant after adjustment for energy intake)	No
Steinmetz et al 1993[20]	Australia	220/438	0.77 (not significant)	No

CRC: Colorectal cancer.

Table 3 Longitudinal studies correlating dietary fiber with colorectal neoplasia

Reference	Location	Cohort	Follow-up period (yr)	Odds ratio of CRC comparing highest to lowest fiber intake groups	Dietary fiberprotective
Fuchs et al 1999[24]	US	88 757 (women)	16	0.95 (95% CI 0.73-1.25)	No
Mai et al 2003[25]	US	45 491 (women)	8.5	0.94 (95% CI 0.71-1.23)	No
Lin et al 2005[26]	US	36 976 (women)	10	0.75 (95% CI 0.48-1.17)	No
Otani et al 2006[27]	Japan	86 412	10	Hazard ratio of lowest fiber intake group compared to highest group: 2.3 (95% CI 1.0-5.2)	No
Shin et al 2006[28]	China	73 314 (women)	5.7	1.1 (95% CI 0.6-1.8)	No

CRC: Colorectal cancer.

Table 4 Intervention studies correlating dietary fiber with colorectal neoplasia

Reference	Setting	n	Intervention	End point	Odds ratio of recurrence in intervention group	Dietary fiber protective
Alberts et al 2000[30]	Postpolypectomy	2079	Counselling	Recurrent adenoma at 4 yr	0.88 (95% CI 0.70-1.11)	No
Schatzkin et al 2000[31]	Postpolypectomy	1429	Fiber supplement	Recurrent adenoma at 36 mo	1.00 (95% CI 0.90-1.12)	No
Ishikawa et al 2005[33]	Postpolypectomy	398	Fiber supplement	Recurrent adenoma at 4 yr	1.31 (95% CI 0.87-1.98)	No
Jacobs et al 2006[34]	Postpolypectomy	3209	Fiber supplement	Recurrent adenoma	0.91 (95% CI 0.78-1.06)	No
		Pooled from 2 studies