Diet composition and age determine the effects of inulin-type fructans on intestinal calcium absorption in rat

Background Although several studies in animals and humans have established that inulintype fructans (inulin, oligofructose, fructooligosaccharides) enhance intestinal Ca absorption, there are also reports that failed to demonstrate any effects of added fructans on Ca absorption. Aim of the study We investigated in a rat model what variables determine inulin actions on mineral absorption with special focus on the basic diet. Methods To determine apparent intestinal mineral absorption, whole body retention and mineral accumulation in bone, we performed feeding experiments with a balance technique by which mineral intake, faecal and urinary output are determined. Results In a first study we compared the effects of an inulin oligofructose mixture (0 and 10%,respectively) when added either to a standard diet or a semi-synthetic diet. Rats fed the semi-synthetic diet were younger (adolescent) than rats on standard diet (young adult). We observed that the apparent Ca absorption ratio was significantly increased by inulin and oligofructose only when provided in the semisynthetic diet and not in the standard diet that intrinsically already contained some fructans from wheat. In our second study with a semi-synthetic diet fed to growing (adolescent) rats, inulin and oligofructose increased not only Ca but also Mg and Zn absorption, whole body mineral retention and femur mineral content. Conclusion Inulin-type fructans at dietary levels of 10 % (w/w) do increase mineral absorption, retention and accumulation in bone in the case of Ca, Mg and Zn, but only when the basic diet for the control group contains no intrinsic fructans and when the mineral demand is particularly high as during growth.