Availability of calcium for absorption in the small intestine and colon from diets containing available and unavailable carbohydrates: an in vitro assessment.

An in vitro method simulating conditions in the small intestine and colon was used to study the effects of various carbohydrates on Ca release from basal diet (BD) containing dairy products. During enzymatic digestion of BD, 28.5 +/- 0.3% of the Ca was released. This was reduced by 3, 22 and 27% by adding bread, psyllium or pectin to BD, respectively (P < 0.05). After enzymatic digestion, the residue from BD was fermented releasing 11.9 +/- 1.2% of the Ca, a value which was significantly less than with pectin (13.7 +/- 0.9%) and greater than with psyllium (4.4 +/- 0.2%) addition. The total Ca release ranged from 26.5 +/- 0.8 to 42.2 +/- 1.0% with bread>BD>pectin>psyllium. Lactulose did not differ significantly from BD. These results suggest that carbohydrates may bind Ca and reduce its availability for absorption in the small intestine. However, if the carbohydrate is fermented, bound Ca may be released for potential absorption in the colon, whereas less fermented carbohydrates may continue to bind Ca in the colon. The in vitro method described may be useful for estimating total Ca availability. However, studies in humans are required to validate these results.