Marie-Anne Levrat-Verny

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.

Apple favourably affects parameters of cholesterol metabolism and of anti-oxidative protection in cholesterol-fed rats

Abstract The effects of apples on lipid metabolism were studied on 40 male Wistar rats adapted to semi-purified diets containing 0.3% cholesterol. In the experimental ‘apple’ diet, a part of starch (15%) was replaced by lyophilized apple (Gala variety). In the control diet, 13% of carbohydrate was replaced by a mixture of fructose/glucose/saccharose to match the sugar supply from the apples. The lipid source was corn oil and the dietary supply of vitamin E was reduced to 1/3 of the recommended value. The rats were sampled after 21 days adaptation. The fibre supply of the apple diet was notably low (about 2%); nevertheless, there was a slight but significant cholesterol-lowering effect in plasma, as well as in liver where cholesterol esters accumulate with cholesterol diets. The lipoprotein profile was markedly altered in apple-fed rats: a reduction of cholesterol in the triglyceride rich lipoprotein (TGRLP) fraction, together with a rise in the HDL fraction; hence there was a favourable effect in a cardiovascular protection perspective. This was paralleled by effects of the apple on cholesterol apparent absorption, which was markedly depressed, whereas bile acid digestive balance was unaffected. In parallel, there was a positive effect of the apple diet on parameters of oxidative stress prevention: higher FRAP plasma levels than in controls, together with a reduced MDA excretion in urine. In conclusion, the present work indicates that a moderate supply of dessert apples elicits interesting effects on lipid and peroxidation parameters.

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.

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.