INTERACTIVE EFFECTS OF CALCIUM AND SHORT CHAIN FATTY-ACIDS ON ABSORPTION IN THE DISTAL COLON OF MAN

Dietary fibers may entrap or bind with minerals and inhibit their absorption in the small intestine. Nevertheless, their fermentation by bacteria present in the colon may produce short chain fatty acids (SCFA) and release the minerals for potential absorption. To determine whether SCFA can enhance calcium absorption from the colon, six healthy male subjects were given rectal infusions of isotonic solutions of saline with and without the addition of Ca and SCFA. The results showed a significant increase in serum Ca after the addition of graded doses of SCFA to rectal infusions containing 30 mmoles Ca (mean increments of serum Ca in mmoles/L: 0 mmoles SCFA = 0.02+/-.04, 22.5 mmoles SCFA = 0.05+/-.05, 45 mmoles SCFA = 0.27+/-.02; P<0.0001). However, increasing amounts of Ca added to 45 mmoles SCFA resulted in a significant decrease in the serum acetate (Ac) response (mean increments of serum Ac in umoles/L: 0 mmoles Ca = 40+/-16, 10 mmoles Ca = 26+/-24, 30 mmoles Ca = 6+/-9; P<0.0001). We conclude that SCFA increase Ca absorption in the distal colon and that Ca may lower serum Ac levels but the mechanism needs further investigation.