Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach.

Literature data on the bioavailability of various Mg forms provide scarce information on the best Mg salt to be used in animal and human supplementation. This study aimed to investigate the bioavailability of different forms of Mg in rats using Mg stable isotopes. Eighty male Wistar rats aged 6 weeks were fed a semi-purified Mg-depleted diet for three weeks. The rats were then randomised into ten groups and received, for two more weeks, the same diet repleted with Mg (550 mg Mg/kg) as: oxide, chloride, sulphate, carbonate, acetate, pidolate, citrate, gluconate, lactate or aspartate. After 10 days of Mg-repleted diet, the rats received orally 1.8 mg of an enriched 26Mg. Faeces and urine were then collected for 4 consecutive days. Isotope ratios in faeces and urine were determined. The Mg absorption values obtained varied from 50% to 67%. Organic Mg salts were slightly more available than inorganic Mg salts. Mg gluconate exhibited the highest Mg bioavailability of the ten Mg salts studied. Urinary 26Mg excretion varied from 0.20 mg to 0.33 mg, and feeding with the organic pidolate, citrate, gluconate and aspartate salts resulted in higher urinary 26Mg excretion than with inorganic salts. Ultimately, 26Mg retention was higher in the rats receiving the organic salts such as gluconate, lactate and aspartate than in those receiving the inorganic salts. Taken together, these results indicate that 26Mg is sufficiently bioavailable from the ten different Mg salts studied in the present experiment, although Mg gluconate exhibited the highest bioavailability under these experimental conditions.

Energy value of a low-digestible carbohydrate, NUTRIOSE FB, and its impact on magnesium, calcium and zinc apparent absorption and retention in healthy young men.

BACKGROUND: Long-term consumption of imbalanced diets, poor in dietary fibres, resulted in the prevalence of several nutritional pathologies. However, low digestible carbohydrates (LDC) have many beneficial effects, especially on energy intake, digestive physiology, and mineral absorption. AIM OF THE STUDY: To determine the digestive effects of a LDC, called NUTRIOSE FB, its metabolisable energy (ME) value, and its effects on mineral absorption in humans. METHODS: Ten healthy young men were fed for 31 d periods a maintenance diet supplemented with either dextrose or the LDC at a level of 100 g DM/d, in six equal doses per d according to a cross-over design. After a 20 d adaptation period, food intake was determined for 11 days using the duplicate meal method, and faeces and urine were collected for 10 d for further analyses. RESULTS: Ingestion of the LDC did not cause severe digestive disorders, except excessive gas emission, and flatulence and slight abdominal pain in some subjects for intakes above 50 g DM/d. Wet and dry stool outputs increased by 45 and 70%, respectively (P<0.02). In vitro enzymatic digestibility of the LDC was 15 (SD 1.5) %, and 9.2 (SD 8.3) % of the LDC was excreted in faeces (P<0.001). The ME value of the LDC was 14.1 (SD 2.3) kJ/g DM, that is 14 % less than the tabulated values of sucrose and starch. Its net energy value (NEV), estimated using three prediction equations, was 8.7, 8.9, and 11.4 kJ/g DM. Ingestion of the LDC significantly increased the relative apparent absorption of Mg, and Mg retention by 67% and 31 mg/d, respectively, tended to increase Ca apparent absorption (P=0.110) and Ca retention (P=0.059), but did not significantly alter Zn parameters. CONCLUSION: NUTRIOSE FB can be used as a "bulking" agent, and substituted up to 50 g/d for usual maltodextrins without causing digestive disorders in healthy subjects. It would reduce intestinal transit disorders and energy intake, and improve magnesium and calcium absorption and retention.

Mineral supplementation of white wheat flour is necessary to maintain adequate mineral status and bone characteristics in rats.

This experiment was designed to compare the effect of ingestion of a wheat flours on mineral status and bone characteristics in rats. White flour was tested either without further mineral supplementation or with Mg, Fe, Zn and Cu supplementation. The flour diets were compared to a control purified diet. Four groups of 10 male Wistar rats each were fed one of the experimental diets for 6 wk and mineral status and tissue retention as well as bone characteristics were determined. As expected, mineral intake, except for calcium, was significantly lesser in rats fed the white flour diet than in the other groups. The rats fed the white flour diet had the lowest food intake, weight gain, fecal excretion and intestinal fermentation. The most important result was that Mg and Fe status were drastically lower in rats fed the white flour diet than in those fed whole flour or control diets. The status of these both elements were significantly improved by the mineral supplementation of white flour. There were no major significant differences between mineral-supplemented white flour and whole flour groups in mineral status. Furthermore, bone mineral densities (total, metaphyseal and diphyseal) were significantly lower in rats fed white flour diet compared to the other diet groups, while no significant difference was observed between the mineral-supplemented white flour, whole flour or control diet groups. In conclusion, the present work shows clearly the importance of mineral-supplementation of white wheat flour to sustain an adequate intake of minerals. Our results indicate also that the whole wheat flour did not negatively alter mineral bioavailability, in comparison to mineral supplemented white flour. Clinical studies are still needed to confirm these rat results in human.

The rhamnogalacturonan-II dimer decreases intestinal absorption and tissue accumulation of lead in rats.

The rhamnogalacturonan-II dimer (dRG-II) forms strong complexes in vitro with lead (Pb) and other selected cations. We examined the in vivo bioavailability of Pb complexed with dRG-II and the effect of unleaded dRG-II on the intestinal absorption and tissue retention of Pb in rats. Forty male Wistar rats were divided into four groups. Each group consumed a purified control diet for 3 wk or the same diet supplemented with: i) 3 mg of Pb/kg, ii) 0.5 g of leaded dRG-II/kg, or iii) 0.5 g of leaded dRG-II/kg and 4.5 g of unleaded dRG-II/kg. The leaded dRG-II provided approximately 3 mg of Pb/kg of diet. A chemical balance study was conducted during the last 5 d of the 3-wk study, and blood and organs were sampled for Pb and mineral analyses. The apparent intestinal absorptions of Pb were 62.3, 15.2, 11.8 and -0.1%, and Pb balances were 1.9, 9.6, 5.6 and -0.2 microg/d for the control and the three experimental groups, respectively. The Pb complexed with dRG-II was less available than Pb acetate, as reflected by significantly lower blood and tissue Pb levels. The addition of unleaded dRG-II decreased the intestinal absorption and the tissue retention of Pb significantly. We further found that the apparent absorption and status of magnesium, zinc and iron were unaffected by Pb treatment or dRG-II addition. We conclude that dRG-II may be useful in decreasing toxicity related to chronic Pb exposure. Human studies will be necessary however, to further evaluate the clinical utility of this beneficial effect.

Comparative relationship between copper-zinc plasma concentrations and superoxide dismutase activity in camels and cows.

On an experimental farm, five camels and five cows were fed with a similar basal diet over a 6-month period. They received an oral trace element supplement for 3 months (days 22-112). This supplement contained zinc and copper sulphate, and corresponded to twice the daily requirement generally recommended for cows. Plasma zinc and copper concentrations were significantly lower in camels (44 micrograms/100 mL for copper and 38 micrograms/100 mL for zinc) than in cows (106 and 83 micrograms/100 mL, respectively). The supplementation had no effect on the plasma zinc concentration in the camels in spite of the low observed values. The mean erythrocyte SOD activity was also significantly higher in the cows (2,404 +/- 211 IU/100 gHb) than in the camels (1,720 +/- 312 IU/100 gHb). In both species, no correlation was found between copper plasma concentration and erythrocyte SOD activity. In cows, a positive relationship was observed between plasma zinc concentration and SOD activity (r = 0.396). In contrast, a negative relationship was found in camels (r = -0.369). These results are discussed in relation to the physiological peculiarities of the camel.

Comparative study of copper and zinc metabolism in cattle and camel.

At an experimental farm, five camels and five cows were fed a similar basal diet for 6 mo. They received oral trace element supplementation for 3 mo (day 22-112). This supplementation included zinc, copper, selenium, manganese, iodine, and cobalt, and corresponded to twice the requirements generally recommended for cows. Plasma copper and zinc concentrations were significantly lower in the camels (61 micrograms/100 mL for copper and 38 micrograms/100 mL for zinc) than in the cows (111 and 83, respectively). The supplementation had no effect on plasma zinc concentration in the camels in spite of the low observed values in this species. Liver copper concentration at the beginning of the trial was lower in the camels (9 ppm) than in the cows (35 ppm), and stayed at lower levels during the entire supplementation period. There was no clear difference in fecal excretion of copper and zinc between the camels and the cows. The results suggested that trace element requirements are lower in camels than in cows and that camels regulate their plasma zinc concentration at a very low level (< 40 micrograms/100 mL).

Parathyroid hormone-related peptide might stimulate calcium secretion into the milk of goats.

Parathyroid hormone-related peptide (PTHrP) has been shown to stimulate the placental calcium pump in pregnant ewes. Recent studies also suggest a physiological role for this peptide during lactation. In the present work, we have studied the possible role of synthetic human PTHrP(1-34), (1-86) and (140-173) fragments on calcium, inorganic phosphorus and magnesium secretion into milk of four adult goats in early lactation. This was done by measuring differences in calcium, inorganic phosphorus and magnesium concentrations in the carotid artery and superficial epigastric vein, the concentration of these minerals in milk and milk production. Both PTHrP(1-34) and (1-86) fragments stimulated calcium, inorganic phosphorus and magnesium uptake by the mammary gland and secretion into milk, without any significant effect on milk production. Therefore PTHrP might have important physiological roles in the pregnant and/or lactating female, by regulating calcium transport through the placenta and mammary gland.

The influence of sulfur supplementation (methionine and sulfate) on the zinc availability of a poor diet in sheep.

A poor hay, with a low proteic level, decreases the zinc availability in lambs. Increasing the sulfur level with methionine and sulfate, of such a diet, enhances zinc absorption. However, sulfur is not the only factor limiting zinc availability in a hypoproteic diet.

A zinc-deficient diet for ruminants: diagnosis and treatment of deficiency.

A zinc deficient diet which is not semi-synthetic was tried on 20 male Limousin X Romanoff three and a half month-old sheep weighing 36 kg on average. This diet was composed of strawy hay sprayed with caramel containing urea and minerals. Compared to hay alone this diet is more appetizing to lambs and more equilibrated as to energy level and soluble nitrogen utilization. The deficiency appeared within a week in zinc plasma and progressed clinically within 100 days. The plasmic free zinc and alkaline phosphatase were not better criteria for the deficiency diagnosis than total plasmic zinc. Supplementing the diet to 50 or even 100 mg Zn/kg DM was insufficient to suppress the deficiency. Zinc injection, by contrast, restored zincemia to normal in ten days. Zinc deficiency treatment by oral route should be reconsidered.