Hubert W. Lopez

Fructooligosaccharides enhance mineral apparent absorption and counteract the deleterious effects of phytic acid on mineral homeostasis in rats

Phytic acid (PA) and fructooligosaccharides (FOS) such as inulin are two food components that are able to modify mineral absorption negatively or positively. The influence of PA and FOS on the cecal and apparent mineral absorption as well as on the mineral status (plasma, hepatic, and bone) were investigated in four groups of rats fed one of the experimental diets: a fiber-free (FF) diet, a FF diet containing 7 g/kg PA (FF + PA), a diet containing 100 g/kg inulin (FOS), or a FOS diet containing 7 g/kg PA (FOS + PA). The cecal enlargement together with the acidification of cecal pH in rats adapted to FOS diets led to an improved Ca and Mg cecal absorption. Mineral apparent absorption was significantly enhanced by FOS ingestion (Ca, +20%; Mg, +50%; Fe, +23%; Cu, +45%), whereas PA decreased this factor only for trace elements (Fe, -48%; Zn, -62%; Cu, -31%). These inhibitory effects of a FF + PA diet have repercussions on blood (Mg, -15%; Fe, -12%; transferrin saturation -31%), liver (Mg, -18%; Fe, -42%; Zn, -25%), and bone (Zn, -25%) variables. However, the introduction of FOS into a PA diet counteracted these observed deleterious effects by stimulating bacterial hydrolysis of PA (+60% in rats adapted to FOS + PA compared to those fed the FF + PA diet) and by improving cecal absorption of minerals.

Effects of soluble corn bran arabinoxylans on cecal digestion, lipid metabolism, and mineral balance (Ca, Mg) in rats

The effects of soluble corn bran arabinoxylans on cecal digestion, lipid metabolism, and mineral utilization [calcium (Ca) and magnesium (Mg)] were investigated in rats adapted to semipurified diets. The diets provided either 710 g/kg wheat starch alone (control) or 610 g/kg wheat starch plus 100 g/kg corn soluble fiber (arabinoxylans) and either 0 or 2 g/kg cholesterol (control + cholesterol and arabinoxylans + cholesterol, respectively). Compared with rats fed the control diets, rats fed the arabinoxylan diets had significant cecal hypertrophy (+50% after 3 days of the fiber adaptation) and an accumulation of short-chain fatty acids, especially propionic acid (up to 45% in molar percentage). Arabinoxylans enhanced the cecal absorption of Ca and Mg (from 0.07 to 0.19 micromol/min for Ca and from 0.05 to 0.23 micromol/min for Mg). Mg balance was enhanced by arabinoxylans (+25%). The arabinoxylan diet markedly reduced the cholesterol absorption from 50% of ingested cholesterol in controls up to approximately 15% in rats adapted to the arabinoxylans diet. Arabinoxylans were effective in lowering plasma cholesterol (approximately -20%). There was practically no effect of the diets on cholesterol in d > 1.040 lipoproteins (high density lipoproteins) whereas arabinoxylans were very effective in depressing cholesterol in d < 1.040 lipoproteins (especially in triglyceride-rich lipoproteins). Corn fermentable fiber decreased the accumulation of cholesterol in the liver. In parallel, the arabinoxylan diet counteracted the downregulation of 3-hydroxy-3-methylglutaryl-CoA by cholesterol. These data suggest that arabinoxylans may have a great impact on intestinal fermentation, mineral utilization, and cholesterol metabolism.

Making bread with sourdough improves mineral bioavailability from reconstituted whole wheat flour in rats

OBJECTIVE We compared the effects of different kinds of bread fermentation on mineral bioavailability. METHODS Wistar rats were fed one of the following experimental diets for 21 d: control, reconstituted whole wheat flour (white flour plus bran), yeast bread, and sourdough bread. The apparent mineral absorption and intestinal fermentation were measured in each animal. RESULTS Phytate contents in yeast and sourdough bread were lower than in reconstituted whole wheat flour (-52% and -71%, respectively). Total cecal pool of short-chain fatty acids, in particular the butyrate pool, was significantly increased by the ingestion of unrefined products. Calcium homeostasis was not modified by these nutritional conditions, whereas magnesium absorption was significantly greater in rats fed the control and sourdough diets than in those consuming whole wheat flour and yeast bread. Magnesium kidney excretion was slightly stimulated by sourdough bread. Compared with the control diet, iron balance was significantly reduced by reconstituted whole wheat flour diet. Yeast bread making counteracted the deleterious effects of whole wheat on iron absorption, whereas sourdough bread making enhanced iron absorption. Further, liver and plasma iron and transferrin saturation levels were lower in rats adapted to the flour diet than in other groups. Zinc absorption was strongly depressed in the presence of unprocessed reconstituted whole wheat flour in the diet, but yeast fermentation afforded a zinc assimilation comparable to the control diet, whereas the sourdough bread led to maximal zinc absorption. Copper absorption increased significantly when rats were fed the sourdough bread, whereas unprocessed whole flour depressed copper absorption (-41% versus control diet). CONCLUSION Mineral bioavailability from reconstituted whole wheat flour can be improved by bread making. Although yeast fermentation minimizes the unfavorable effects of phytic acid, sourdough bread is a better source of available minerals, especially magnesium, iron, and zinc.

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.

Whole wheat flour exerts cholesterol-lowering in rats in its native form and after use in bread-making

The ingestion of whole wheat flour (WWF) has been shown to exert lipid-lowering effects in rats but WWF is generally consumed after being processed (fermentation, starch gelatinization, heating). It remains to be assessed whether bread making has an influence on the potential lipid-lowering properties of flours. For this purpose, rats were fed semi-purified diets containing 70% WWF, or the same percentage of desiccated whole wheat bread (WWB) and the control group was fed with fibre-free purified starch diet. All the cereal diets showed a cholesterol-lowering effect in plasma and liver compared to control, but there was a more pronounced plasma triglyceride-lowering effect in rats fed WWB. In parallel, total steroids excretion was significantly enhanced (P <0.01) by the cereal diets, but to a greater extent by WWB. As a result, cholesterol absorption percentage was also markedly reduced in rats fed WWB diet (around 26%, compared to 38% for WWF and 52% for controls). WWF and WWB yielded butyric acid rich fermentations in the cecum, compared to the control diet, and WWB markedly enhanced propionic acid production compared to WWF. In conclusion, the baking process adds significantly to the hypolipemic effects observed previously with WWF, in spite of reduced specific viscosity.

Wheat Varie1y has a Maior Influence on Mineral Bioavailability; Studies in Rats

The aim of this study was to compare mineral bioavailability of four soft wheat varieties (Soissons, Hardi, KON2, BNC) in rats. If intestinal fermentation was stimulated by four diets compared to control diets, the incorporation of 70% of whole wheat flour in the rat diet did not modify Ca bioavailability. Nevertheless, Mg absorption and accumulation in bone were stimulated by the ingestion of KON2 and BNC varieties. Feeding KON2 or BNC varieties significantly increased iron absorption and status compared to the other three groups. Zinc absorption was significantly depressed by Soissons flour (- 28% ), whereas the three other whole wheat flour diets led to a better zinc assimilation compared to the control group. The consumption of Hardi, KON2 or BNC wheat varieties had percussions on liver zinc ( + 29%, + 36% and + 33% compared to control group, respectively). Copper absorption was significantly increased by KON2 or BNC varieties ( + 93% and + 88%, respectively), but copper status was not modified by nutritional differences. Moreover, phytate breakdown was higher when the diets contained KON2 or BNC varieties. Mineral bioavailabilities from KON2 or BNC varieties were higher than those observed with Soissons or Hardi varieties. Thus, genetic origin plays a major role in determining mineral bioavailability in whole wheat.

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.