Acidic fermentation in the caecum increases absorption of calcium and magnesium in the large intestine of the rat

Abstract

The effect of fermentation on colonic absorption of Ca and Mg was investigated in 8-week-old rats adapted to diets containing either digestible wheat starch (DS diets) or including resistant starch, i.e. 350 g raw potato starch/kg (RS diets). The dietary Ca level of the DS and RS diets was 2.5 or 7.5 g/kg. RS diets resulted in enlargements of the caecum together with hypertrophy of the caecal wall. Acidification of the caecal contents by microbial fermentation of RS was influenced by the dietary Ca level. Very acidic pH conditions and relatively low concentrations of short-chain fatty acids, in the presence of lactic acid fermentation, were observed with the 2.5 g Ca/kg level. Rats fed on RS diets had a higher percentage of soluble Ca (and inorganic phosphate) in the caecum, particularly of rats adapted to the high Ca level. As a result of the hypertrophy of the caecal wall and of an elevated concentration of soluble Ca, the caecal absorption of Ca was 5-6-fold higher in the RS groups than in the DS groups. The difference between dietary intake and faecal excretion (DI-FE) of Ca was higher in rats fed on RS diets than in those fed on DS diets, when the dietary Ca level was 2.5 g/kg. With the higher Ca intake the elevated rate of Ca absorption from the caecum in RS-fed rats was not paralleled by an enhanced DI-EE difference: this suggests a shift of the Ca absorption towards the large intestine. Feeding RS diets also enhanced Mg caecal absorption, resulting in a substantially higher DI-FE difference for Mg, especially with the 2.5 g Ca/kg diets, because a high Ca intake tends to inhibit Mg absorption. The present findings support the view that the large intestine may represent a major site of Ca (and Mg) absorption when acidic fermentations take place. This process could improve the digestive Ca balance when the dietary Ca supply is low; when the Ca supply is affluent, it rather shifts Ca absorption towards a more distal site of the digestive tract.

Effect of soluble or partly soluble dietary fibres supplementation on absorption and balance of calcium, magnesium, iron and zinc in healthy young men

“…This is the ®rst time, to our knowledge, that such an effect has been observed in humans. These results con®rm previously reported data from animal investigations in our own laboratory, (Demigne  et al, 1989;Levrat et al, 1991;Younes et al, 1996), and by other workers (Delzenne et al, 1995;Ohta et al, 1995). Several hypothesis about the mechanisms of the effect of inulin on Ca absorption could be proposed.…”

Long-Term Administration of 4G-.BETA.-D-Galactosylsucrose (Lactosucrose) Enhances Intestinal Calcium Absorption in Young Women: A Randomized, Placebo-Controlled 96-wk Study

“…Several hypotheses have been advanced to explain the potential positive effect of NOD on intestinal mineral absorption in animals. Colonic fermentation of NOD leads to the formation of high concentrations of shortchain fatty acids (SCFA) and the presence of Ca 2 ϩ and Mg 2 ϩ in the colonic lumen ( 13,14). In addition, it has been hypothesized that NOD stimulate transcellular calcium absorption by a direct effect of the SCFA that are produced (15,16).…”

Molecular Mechanism of the Effect of Fructooligosaccharides on Calcium Absorption

“…Although these acids have important physiological effects in their own right, they also act to lower the pH of the lumen. This luminal environment may facilitate a change in calcium salts from insoluble to soluble form and thus increase the diffusive absorption of calcium via the paracellular route (9,44,51). According to this hypothesis, indigestible carbohydrates need not elicit any biochemical effects such as the activation or deac- Fig.…”