Fiber

Fiber: What is it?

Other names: Inulin, wheat bran, beta-glucan, psyllium.

Mechanism of action:

Postprandial glycemic control: Gel-forming fibers, such as psyllium or β-glucan will increase viscosity of chyme in the small intestine. By increasing the viscosity, it slows the interactions of digestive enzymes with nutrients, thus slowing down the absorption of glucose, leading to reduced peak of postprandial blood glucose concentration. Long term, it has been shown to improve glycemic control in type 2 diabetics.

The physical increase in chyme viscosity can also lower elevated serum cholesterol concentration by trapping and eliminating bile. As chyme becomes more viscous, bile's window for reuptake becomes smaller, causing bile to be lost in stool. Reduction of bile acid causes hepatocytes to stimulate LDL-receptor expression leading to increased LDL-cholesterol clearance from blood to synthesize more bile acids.

Laxative effect in two ways: Insoluble fiber (wheat bran) does not dissolve in water well; thus they mechanically irritate the gut mucosa, stimulating water secretion helping to soften stool and secondly, soluble gel-forming fiber retains high water hold capacity, helping to resist dehydration in the large bowel. Both result in soft and easy-to-pass stools.

Common indications/uses:

The use of viscous gel-forming fiber (aka psyllium) is indicated for lowering cholesterol, improving glycemic control, constipation, and IBS.

Dosing:

25 g of fiber per day for women, 38 g of fiber per day for men.

Evidence:

A study done by the American college of Gastroenterology Chronic Constipation Task Force systematically reviewed clinical evidence and concluded that only psyllium was sufficient for the treatment of chronic constipation.

A 6-month study was done to compare the effects of viscosity on weight loss by assessing a viscous, gel-forming, nonfermented fiber (psyllium) versus a less viscous, readily fermented fiber (partially hydrolyzed guar gum). In this randomized control study, the psyllium treatment group showed gradual and sustained weight loss across the entire 6-month test period. After 6-months, there was significant improvement in fasting plasma glucose, hemoglobin A1C, and LDL-cholesterol levels.

Safety concerns:

Adverse reactions: Abdominal bloating and gas.

Drug interactions:

May interact with tricyclic antidepressants, glyburide, metformin, carbamazepine, cholestyramine, colestipol, digoxin, lithium.