Effect of fermentation of folate bioavailability.
The objective of this study was to assess the association between dietary fibre (DF) and fermentable substrates (FS) intake, colonic bacterial fermentation, and folate bioavailability. Folate is important in human nutrition because folate deficiencies are associated with neural tube defects and anaemia and excess folate intake may mask other disease states. Folate may also modulate hyperhomocysteynemia, an independent risk factor for cardiovascular disease. Current recommended intakes (400 ug/d) are based solely on folacin intake but it has been suggested that folacin may also be obtained indirectly from colonic bacteria, stimulated by fermentation of DF and FS. In order to study this possibility, male weanling Sprague Dawley rats were folate depleted by feeding a low folacin AIN93G formulated basal diet for 28 d and then fed diets differing in DF or FS and folate (0.25-1.0 mg/kg diet) to replete liver stories. During the repletion phase, the increase in liver folate was proportional only to the dietary folate content and did not vary with changing dietary DF or FS. An antibiotic (succinylsulfathiazole) was added to inhibit gut bacterial populations and bacterial fermentation. Addition of the antibiotic lowered total liver folate in controls and test diets equally suggesting an effect of succinylsulfathiazole on folate absorption or metabolism. Changes in cecal volatile fatty acids, increases in fecal diaminopimelic acid excretion, DF or FS balance as well as increases in fecal folate content provided evidence for an increased bacterial fermentation, an increased bacterial excretion, and an increased production of folate in the colon. However, colonic folate produced by bacterial fermentation was not bioavailable.