Jacques Bellanger

Effects of two fermentable carbohydrates (inulin and resistant starch) and their combination on calcium and magnesium balance in rats

Resistant starch and inulin are complex carbohydrates that are fermented by the microflora and known to increase colonic absorption of minerals in animals. The fermentation of these substrates in the large bowel to short-chain fatty acids is the main reason for this increase in mineral absorption. The purpose of the present study was to examine the potential synergistic effect of a combination of these two fermentable carbohydrates. For this purpose, thirty-two adult male Wistar rats weighing 200 g were used in the present study. The rats were distributed into four groups, and fed for 21 d a fibre-free basal purified diet or diet containing 100 g inulin, or 150 g resistant starch (raw potato starch)/kg diet or a blend of 50 g inulin and 75 g resistant starch/kg diet. After an adaptation period of 14 d, the rats were then transferred to metabolic cages and dietary intake, faeces and urine were monitored for 5 d. The animals were then anaesthetized and caecal Ca and Mg absorption were measured. Finally, the rats were killed and blood, caecum and tissues were sampled. Ca and Mg levels were assessed in diets, faeces, urine, caecum and plasma by atomic absorption spectrometry. Our results confirmed that inulin and resistant starch ingestion led to considerable caecal fermentation in the three experimental groups compared with the control group diet. Moreover, both carbohydrates significantly increased the intestinal absorption and balance of Ca and Mg, without altering the plasma level of these two minerals. Interestingly, the combination of the studied carbohydrates increased significantly the caecal soluble Ca and Mg concentrations, the apparent intestinal absorption and balance of Ca, and non-significantly the plasma Mg level. In conclusion, a combination of different carbohydrates showed synergistic effects on intestinal Ca absorption and balance in rats. Further studies with other types of carbohydrate combinations should be carried out to extend these findings.

Resistant starch improves mineral assimilation in rats adapted to a wheat bran diet

Abstract The effects of a natural source of phytic acid (PA) such as wheat bran (WB), in the presence or in the absence of resistant starch (RS) on the assimilation of minerals (Ca, Mg, P) and trace elements (Fe, Mn, Zn, Cu) were investigated in rats adapted to semipurified diets. The diets provided either 73g/100 g digestible wheat starch (DS) alone, or 53 g/100 g DS plus 20 g/100 g raw potato starch (RS) and either 0 or 20 g/100 g WB. Mineral content of all diets was adjusted before the beginning of the experiment. RS diets resulted in enlargements of the cecum together with an accumulation of short-chain fatty acids. As a result of the hypertrophy of the cecal wall, acidification of luminal pH and an elevated concentration of soluble minerals, the cecal absorption of Ca, Mg, and P was 3–5-fold higher in the RS groups than in the DS groups. Mineral apparent retention was significantly enhanced by RS ingestion (Ca, +39%; P, +30%; Mg, +32%; Zn, +47%; Fe, +27%; Mn, +5% and Cu, +37%). WB ingestion altered significantly P solubility and its cecal absorption. Thus, WB exerted a significant effect on P and trace elements balances (P, −29%; Zn, −60%; Fe, −26%; Mn, −22% and Cu, −47%). Nevertheless, with WB diets, the disappearance of phytic acid was 2-fold higher in rats fed the RS than those fed the DS. Thus, the addition of RS into WB diet allows a greater mineral absorption by increasing the organic acids production and the breakdown of PA in the large intestine.

Wholewheat flour ensures higher mineral absorption and bioavailability than white wheat flour in rats.

Consumption of unrefined whole flour is thought to affect mineral bioavailability because it contains high levels of fibre and phytic acid. The present experiment was designed to study the absorption of minerals from diets based on wholewheat flour and white wheat flour in rats. Two groups of male Wistar rats were fed on the diets for 3 weeks and absorption and tissue retention of minerals were studied. The rats fed on the wholewheat flour diet had significantly greater food intake, weight gain, faecal excretion and intestinal fermentation than those fed on the white flour diet. Mineral intakes, except for Ca, were significantly greater in rats fed on the wholewheat flour diet (4-fold for Mg, 2-fold for Fe and Zn). A significant rise in the apparent absorption of Fe (%) and a significant decrease in the apparent absorption of Zn (%) were observed. The amounts of minerals absorbed (mg/d) were significantly enhanced (excepted for Ca) with the wholewheat flour diet. Moreover, plasma and tibia levels of Mg and plasma, liver and tibia levels of Fe were significantly increased in rats fed on the wholewheat flour diet compared with those fed on the white flour diet. In conclusion, wholewheat flour, rich in phytic acid and minerals, did not have a negative effect on mineral absorption, but rather improved the bioavailability of some minerals. Human studies are needed to confirm these rat results before extrapolation to human nutrition.

The effect of dietary copper on rat plasma apolipoprotein B, E plasma levels, and apolipoprotein gene expression in liver and intestine

The plasma levels of apo B and apo E, and the level of hepatic and intestinal mRNA coding for these apolipoproteins were investigated in weanling male rats pair-fed for 6 wk with a control or copperdeficient diet. Plasma cholesterol, triglycerides, and phospholipids were significantly increased, and plasma apo B and apo E levels were also markedly increased in copper-deficient rats as compared to control rats. Copper deficiency significantly increased triglyceride levels and decreased cholesterol levels in the liver. No major differences in the levels of hepatic and intestinal apo B and apo E mRNA occurred between control and copper-deficient rats. These data imply that hypertriglyceridemia dn hypercholesterolemia owing to the copper deficiency are not accompanied by modifications in the gene expression at the mRNA level in the liver and intestine of the apolipoproteins studied.

Effects of Whole Wheat Flour and Fermentable Carbohydrates on Intestinal Absorption of Trace Elements in Rats

If these results can not be directly extrapolated to human nutrition, they show that whole flour or unrefined cereal products ingestion can contribute to improved mineral balance. The cecal fermantation of soluble carbohydrates present in these products may be responsible for such mineral absorption enhancement and adequate mineral balance. Several epidemiological and clinical studies have recently shown growing interest in increasing the consumption of phytic acid-rich products in preventive nutrition. Negative effects of such products on mineral bioavailability may be neutralized when these products are taken together with the other components of the meal. It is thus possible to promote the consumption of whole grains rather than of purified cereal products, to keep functionally active constituents of grains and to optimize the mineral status in humans. Human studies are still needed to confirm these rat results.

Study of Magnesium Absorption Using 25Mg Stable Isotope and Inductively Coupled Plasma/Mass Spectrometry Technique in Rat

Magnesium metabolism is regulated at the intestine and kidneys by controlling the fraction of Mg absorbed from the total dietary intake and by renal homeostasis (1,2). As interest in Mg dietary requirements and metabolism has grown, the need for safe and convenient techniques for measurement of Mg absorption and bioavailability has increased. Balance studies are imprecise, labor intensive, give little information on Mg metabolism and do not consider the endogenous fecal excretion (3). Although kinetic analysis has been performed with the short-lived 28Mg radioisotope, the use of radio isotopes in humans is hazardous and restricts the experiment to a few days duration and is being supplanted by stable isotope methods (4). The use of extrinsic labeling presumes that the administered isotope behaves in the same way and that its absorption is the same as that of endogenous forms of Mg. The validity of the extrinsic labeling approach is now well established (5,6,7). Stable isotopes have been analyzed by two different analytical techniques; neutron activation and mass spectrometry. Although thermal ionization mass spectrometry (TIMS) is the reference technique, inductively coupled argon plasma mass spectrometry (ICP/MS) is also being widely developed (8). ICP/MS has many advantages in stable isotope measurement and has been applied to metabolic studies of many different minerals. In the present work, the feasibility of using a Mg stable isotope and ICP/MS technique to study Mg absorption and metabolism was explored in adult rats and the optimum dosage of the isotope was investigated.