Effect of a high-protein diet on maintenance of blood pressure levels achieved after initial weight loss: the DiOGenes randomized study.

Randomized trials have shown significant blood pressure (BP) reductions after increased protein compared with carbohydrate intake, but the effect on BP maintenance after initial weight loss is unclear. We examined the effect of a high-protein diet on the maintenance of reduced BP after weight loss in 420 overweight adults from the Diet, Obesity and Genes study. After an 8-week weight-loss period (>8% BW), subjects (42±6 years) were randomized to either a high-protein diet (23-28 en% protein) or a lower-protein control diet (10-15 en% protein) for 26 weeks. BMI after weight loss was 30.3±4.3 kg m(-2), BP was 118/73 mm Hg and 28 subjects (6.5%) used antihypertensive agents. Systolic BP during 26 weeks of weight maintenance dietary intervention increased in both treatment groups, but it was 2.2 mm Hg less (95% CI: -4.6 to 0.2 mm Hg, P=0.08) in the high-protein group than in the lower-protein control group. In 191 (pre)hypertensive subjects (baseline systolic BP⩾120 mm Hg), a larger difference was observed (-4.2 mm Hg (-7.7, -0.7), P=0.02). The effect was attenuated after adjustment for initial BP (-3.4 mm Hg (-6.9, -0.03), P=0.048), and after additional adjustment for weight change (-2.7 mm Hg (-6.1, 0.4), P=0.11). Adjustment for 24-h urinary excretion of sodium and potassium did not change the results. Diastolic BP yielded similar results. These findings suggest that a BP reduction after weight loss is better maintained when the intake of protein is increased at the expense of carbohydrates. This effect is partly mediated by body weight.

Intake of total protein, plant protein and animal protein in relation to blood pressure: a meta-analysis of observational and intervention studies.

There is growing evidence from epidemiological studies that dietary protein may beneficially influence blood pressure (BP), but findings are inconclusive. We performed a meta-analysis of 29 observational studies and randomized controlled trials (RCTs) of dietary protein and types of protein in relation to BP or incident hypertension, published until January 2012. The analysis included eight cross-sectional studies (n=48 985), four prospective studies (n=11 761) and 17 RCTs (n=1449). A modest inverse association between total protein intake and BP (-0.20 mm Hg systolic (95% CI: -0.39, -0.01) per 25 g (∼1 s.d.)) was found in cross-sectional studies, but not in prospective studies (relative risk of 0.99 (95% CI: 0.96, 1.02)). For RCTs that used carbohydrate as a control treatment, the pooled BP effect was -2.11 mm Hg systolic (95% CI: -2.86, -1.37) for a weighed mean contrast in protein intake of 41 g per day. A non-significant inverse association of -0.52 mm Hg systolic (95% CI: -1.10, +0.05) per 11 g (∼1 s.d.) was found for plant protein in cross-sectional studies, whereas animal protein was not associated with BP. In prospective studies and RCTs, however, the associations of plant protein and animal protein with BP were broadly similar. These findings suggest that increasing the intake of protein at the expense of carbohydrates may have a beneficial effect on BP. The BP effect of specific types of protein remains to be established.

Epigallocatechin gallate (EGCG) (TEAVIGO) does not impair nonhaem-iron absorption in man.

A number of studies have shown that tea catechins can inhibit intestinal iron absorption, mostly iron in the nonhaem form. This randomized, double-blind, placebo-controlled, 3-periods cross-over study examined the degree of inhibition of nonhaem iron absorption by pure crystalline epigallocatechin gallate (EGCG). The study was designed to show the maximum inhibitory action of EGCG by selecting 30 healthy women with low iron stores. Treatments were 150 mg, 300 mg EGCG and placebo each for 8 consecutive study days with a wash-out period of 14 days between treatments. Iron incorporation was assessed by supplying 57Fe orally and 58Fe intravenously. Differences in fractional nonhaem iron absorption between the treatments were evaluated by using two-sided ANOVA. Results showed a relative nonhaem iron absorption reduction of 14% with 150mg EGCG and 27% for 300mg EGCG treatment compared to placebo. Differences were statistically significant (p < or = 0.05) between the placebo and the 300mg EGCG treatments and between the 150 and 300 mg EGCG treatments. The inverse relation between EGCG dose and fractional nonhaem iron absorption was linear (p = 0.0002). In this study the magnitude of the inhibitory action of EGCG on nonhaem iron absorption was found to be much lower than that reported in the literature for black tea and similar compounds. The doses of EGCG in supplements, which will be lower than those used in this study, are not expected to have any health relevant effects on iron absorption in subjects with normal iron stores.

Safety of long-term consumption of plant sterol esters-enriched spread.

OBJECTIVE: To evaluate both efficacy and safety in humans of long-term consumption of spreads containing plant sterol esters. DESIGN: Randomized double-blind placebo-controlled parallel trial. SUBJECTS: : Hundred and eighty-five healthy volunteers (35-64 y). INTERVENTION: Volunteers daily consumed 20 g spread enriched with 1.6 g plant sterols as fatty acid esters or a control spread for 1 y. They continued their habitual diet and lifestyle. Outcome measures included efficacy markers such as total and LDL-cholesterol, a large range of safety parameters, and reporting of adverse events. RESULTS: Consumption of the plant sterol ester-enriched spread consistently lowered total and LDL cholesterol during the 1 y period on average by 4 and 6%, respectively (0.01 < P < 0.05). Plant sterols intake did on average not result in a lower carotenoid concentration (when expressed per LDL-cholesterol) after 52 weeks (P>0.05). However, carotenoid concentrations changed over time. Plant sterols intake reduced lipid adjusted alpha- and beta-carotene-concentrations by only 15-25% after 1 y, relative to control. Lipid-adjusted fat-soluble vitamin concentrations remained unchanged. Plant sterol concentrations in serum were increased from 2.76 to 5.31 ( micro mol/mmol total cholesterol) for campesterol (P<0.0001) and from 1.86 to 2.47 ( micro mol/mmol total cholesterol) for beta-sitosterol (P<0.0001). The increase in total plant sterol concentration in red blood cells (5.29-9.62 micro g/g) did not affect red blood cell deformability. Hormone levels in males (free and total testosterone) and females (luteinizing hormone, follicle stimulating hormone, beta-estradiol and progesterone) as well as all clinical chemical and hematological parameters measured were unaffected. Adverse events reported were not different between subjects consuming control spread and subjects consuming plant sterol esters-enriched spread. CONCLUSION: Consumption of a plant sterol esters-enriched spread is an effective way to consistently lower blood cholesterol concentrations and is safe to use over a long period of time.

Effects of cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid (CLA) isomers on immune function in healthy men.

OBJECTIVES: To study the effects of two different mixtures of the main conjugated linoleic acid (CLA) isomers cis-9, trans-11 CLA and trans-10, cis-12 CLA on human immune function. DESIGN: Double-blind, randomized, parallel, reference-controlled intervention study. SUBJECTS AND INTERVENTION: Seventy-one healthy males aged 31-69 y received one of the following treatments: (1). mixture of 50% c9,t11 CLA and 50% t10,c12 CLA isomers (CLA 50:50); (2). mixture of 80% c9,t11 CLA and 20% t10,c12 CLA isomers (CLA 80:20); and (3). sunflower oil fatty acids (reference). The treatments were given as supplements in softgel capsules providing a total of 1.7 g (c9,t11+t10,c12) CLA fatty acids (50:50) or 1.6 g (c9,t11+t10,c12) CLA glycerides (80:20) per day in treatment groups for 12 weeks. RESULTS: Almost twice as many subjects reached protective antibody levels to hepatitis B when consuming CLA 50:50 fatty acids (15/24, 62%) compared with subjects consuming the reference substance (7/21, 33%, P=0.075). In subjects consuming CLA 80:20 glycerides this was 8/22 (36%). Other aspects of immune function, ie DTH responses, NK cell activity, lymphocyte proliferation and production of TNF-alpha, IL1-beta, IL6, IFN-gamma, IL2, IL4, and PGE(2), were not affected. CONCLUSION: This is the first study that suggests that CLA may beneficially affect the initiation of a specific response to a hepatitis B vaccination. This was seen in the CLA 50:50, but not in the CLA 80:20 group.

Dietary linoleic acid at high and reduced dietary fat level decreases the faecal excretion of vitamin E in young rats.

Vitamin E is the major lipid-soluble antioxidant in human subjects and is crucial in protecting polyunsaturated fatty acids (PUFA) against lipid peroxidation. Dietary PUFA have been suggested to inhibit the absorption of vitamin E. The present study in young male rats was designed to investigate the effect of increasing concentrations of dietary linoleic acid on the faecal excretion of vitamin E. The rats were fed on semi-synthetic diets containing two concentrations of fat (59 g/kg diet, 15 energy % (en%) or 131 g/kg, 30 en%) for 3 weeks. Triacylglycerol rich in linoleic acid was added at the expense of triacylglycerol rich in saturated fatty acids to obtain dietary concentrations of 13, 39 or 66 g linoleic acid/kg diet for the high-fat diet (131 g fat/kg) and 12, 24 or 36 g linoleic acid/kg diet for the reduced-fat diet (59 g fat/kg). The results from the present study demonstrate that the faecal excretion of vitamin E was significantly lower in rats fed on diets with high levels of linoleic acid compared with rats fed on lower levels of linoleic acid irrespective of the dietary fat content. The concentration of vitamin E in liver and plasma was significantly lower in animals fed on the highest concentration of linoleic acid compared with those fed on the lowest level. Results from the present study also demonstrate that at the same concentration of linoleic acid, the faecal excretion of vitamin E in rats fed on reduced-fat diets was significantly lower than in rats fed on high-fat diets. Our findings indicate that the apparent absorption of vitamin E is not inhibited by dietary PUFA. Results from the present study also demonstrate that a reduction of dietary fat content from 30 en% to 15 en% does not lower the apparent absorption of vitamin E.

Dietary ascorbic acid raises iron absorption in anaemic rats through enhancing mucosal iron uptake independent of iron solubility in the digesta.

We studied Fe absorption from FeSO4 in rats with Fe deficiency-induced anaemia that were given an Fe-sufficient purified diet without or with ascorbic acid (10.4 g/kg diet). Attention was focused on mucosal Fe uptake as measured in vivo by a double-isotope technique. Haemoglobin repletion and liver Fe levels were not affected when the ascorbic acid-supplemented diet was given, but apparent Fe absorption and retention of orally administered 59Fe were significantly enhanced. The distribution of Fe between liquid and solid phases of contents of both the stomach and the proximal intestine was not affected by the feeding of the ascorbic acid, but ascorbic acid significantly enhanced mucosal Fe uptake. It is concluded that ascorbic acid in the diet raises mucosal Fe uptake through a mechanism independent of the intestinal Fe solubility.

Vitamin E incorporated into a very-low-fat meal is absorbed from the intestine of young rats.

Vegetable fats and oils are major sources of dietary vitamin E. Consequently the current trend to reduce fat consumption is accompanied by a reduction of the intake of vitamin E. In addition, the absorption of vitamin E is thought to be dependent on the hydrolysis of dietary lipids in the small intestine. It is therefore conceivable that a lower dietary fat intake also diminishes the intestinal absorption of vitamin E. The present 3-week feeding study in young male rats was designed to investigate whether different concentrations of vitamin E added to a very-low-fat product (0, 330 or 1350 mg DL-alpha-tocopheryl acetate/kg product) were absorbed. We therefore incorporated these products into a very-low-fat meal (final fat concentration: 7 g/kg) or a low-fat meal containing 52 g fat/kg. The magnitude of vitamin E absorption from these meals was compared with that from meals containing similar amounts of vitamin E, but a high fat concentration of 190 g/kg. Apparent vitamin E absorption was defined as intake of alpha-tocopherol equivalents (alpha TE) minus faecal alpha TE excretion over 4 d during week 3 of the experimental period. The results of this study showed that apparent absorption of vitamin E from a very-low-fat meal varied, depending on the vitamin E concentration, from 73 to 83%. The magnitude of this vitamin E absorption was not significantly different from that from meals containing a high amount of fat. Liver vitamin E status was equal in rats fed on the very-low-fat meals compared with those fed on the high-fat meals. We conclude that, when very-low-fat or low-fat products are used as a replacement for full-fat products, addition of vitamin E to these products, as DL-alpha-tocopheryl acetate, might be useful in meeting the vitamin E requirements.

Development of computer-assisted patient control for use in the hospital setting during mass casualty incidents.

Hospital resolution of mass casualty incidents can have difficulties involving "command and control" and information management, ineffective use of triage classes, and missed diagnostic procedures, leading to lower quality of care. A computer system has been developed to supply continuously updated group and patient data. The system uses barcoded identifiers to represent patients, injuries, facilities, and locations, in order to minimize errors and make exchange of data possible. The system communicates with the permanent hospital information system. This article reports the use of this technology during several experiments and real incidents. Computer registration based on bar codes, despite the greater number of items entered, still showed 25% fewer inaccuracies when compared with handwritten medical charts. Extensive training was shown to be unnecessary. Paramedical personnel judged the automated procedures to be an improvement during the admission of 143 evacuated patients.

Mechanism underlying the inhibitory effect of high calcium carbonate intake on iron bioavailability from ferrous sulphate in anaemic rats.

The influence of high CaCO3 intake on the bioavailability of Fe from FeSO4 was assessed during Fe repletion of rats with Fe-deficiency-induced anaemia. Fe-deficient rats with a mean blood haemoglobin concentration of 4.1 mmol/l were fed on purified Fe-adequate diets containing either 6.2 or 25.0 g CaCO3/kg (ten rats per group). Haemoglobin repletion after 14 d was significantly depressed by high CaCO3 intake (9.5 v. 9.8 mmol/l for high and low CaCO3 intake respectively; P = 0.03), as was apparent Fe retention (367 v. 552 micrograms/d during days 5-7, P < 0.001; 146 v. 196 micrograms/d during days 19-21, P < 0.001). The concentration of Fe in the liquid phase of the proximal half of the small intestine was significantly lower in the high-CaCO3 group (3.71 v. 5.20 micrograms/g digesta; P = 0.02). Mucosal uptake and mucosal transfer of Fe were determined with orally administered 59Fe and Cr as a non-absorbable marker. Mucosal transfer was significantly diminished by CaCO3 loading (90 v. 100% of mucosal uptake; P = 0.04), whereas mucosal uptake was not. 59Fe retention values at 14 d after administration were not significantly different (57.6 v. 51.9%; P = 0.14). Fe contents of liver and spleen were significantly decreased by high compared with low CaCO3 intake (879 v. 590 micrograms Fe in liver, P < 0.001; 92 v. 63 micrograms Fe in spleen, P < 0.001). It is concluded that high intake of CaCO3 depresses Fe bioavailability in rats. The CaCO3-induced decrease in Fe solubility in the digesta probably was associated with an increased efficiency of mucosal Fe uptake so that the amount of mucosal uptake remained unaltered. The CaCO3-induced decrease in Fe transfer through the mucosal cytoplasm and/or basolateral membrane may have been responsible for the concurrent decrease in Fe bioavailability.

Technique for creating a permanent cecal fistula in the rat.

A method was developed to surgically implant a silicone/stainless steel fistula-cannula in the cecum of freely moving rats. The specially designed fistula-cannula allows sampling of cecal contents at any time without disturbing the physiologic functions of the intestinal tract, as evaluated by observation of general well-being and postmortem macroscopic inspection. The fistula-cannula was implanted in 12 male rats under general anesthesia. The animals remained in good health during the postoperative period lasting up to 9 weeks. They gained weight normally compared with a control group (n = 8) that had not undergone surgery. Samples of 0.2 to 1.0 g of contents could be collected with a microspatula, without the need to anesthetize the animal. The model provides a useful system for sampling cecal contents without the need to sacrifice the animal. Because it allows cross-over studies to be carried out, this approach may result in significantly reducing the number of animals required for digestive studies.

Positional distribution of stearic acid and oleic acid in a triacylglycerol and dietary calcium concentration determines the apparent absorption of these fatty acids in rats.

In this study the effect of the positional distribution of stearic acid (18:0) and oleic acid (18:1) in a triacylglycerol on absorption of fat, energy and nutrients was investigated in young rats. In addition the effect of dietary calcium on these variables was studied. Forty rats were fed purified diets containing either a fat blend high in 2-oleoyl-distearate or a fat blend high in 1-oleoyl-distearate. Both diets were given at low (0.3 g/100 g) and high (1.0 g/100 g) dietary calcium concentrations. Total fat absorption, expressed as the percentage of fat intake, was significantly lower in rats fed 2-oleoyl-distearate compared with 1-oleoyl-distearate at both dietary calcium concentrations. When expressed as absolute figures, the lower fat absorption in rats fed 2-oleoyl-distearate compared with 1-oleoyl-distearate only reached statistical significance at the high dietary calcium concentration. The reduced absorption of total fat was mainly caused by the lower absorption of stearic acid. The percentage of, but not absolute, absorption of oleic acid and energy were lower in rats fed 2-oleoyl-distearate. Absolute and percentage of calcium absorption were lower in rats fed 2-oleoyl-distearate compared with 1-oleoyl-distearate. Absolute and percentage of magnesium absorption were not significantly affected by the positional distribution of stearic acid and oleic acid in the triacylglycerol, but were decreased at a high dietary calcium concentration. We concluded that the lowered stearic acid absorption from 2-oleoyl-distearate compared with 1-oleoyl-distearate might have been due to the greater formation of insoluble calcium and magnesium soaps in the intestine.

Ileal pH and apparent absorption of magnesium in rats fed on diets containing either lactose or lactulose.

The hypothesis was tested that dietary lactose v. glucose stimulates Mg absorption in rats because lactose lowers pH of the ileal lumen, which improves Mg solubility which in turn enhances Mg availability for transport across the ileal epithelium. For comparison, the effects of lactulose were studied because it shares with lactose the characteristic of being poorly digestible. Replacement of glucose by lactose (100 g/kg) significantly stimulated apparent absorption of Mg. Apart from Mg absorption, lactulose also significantly enhanced absorption of Ca and phosphate. Lactose v. glucose lowered the pH of the ileal lumen from 7.5 to 7.2, whereas lactulose significantly reduced it to 7.0. In in vitro incubations a decrease in pH within the range of fluctuation in vivo was found to cause an improved solubility of Mg, and to a lesser extent also of Ca and phosphate. The smaller fall of ileal pH induced by feeding lactose instead of lactulose may explain why lactose improved Mg absorption only. For all individual rats combined there were negative relationships between ileal pH and apparent absorption of minerals, the relationship being strongest for Mg. Neither lactose nor lactulose was found to raise ileal solubility of minerals, which could relate to the possibility that the time of sampling was not appropriate. It is suggested that lactose-induced stimulation of Mg absorption in rats is caused by a lowering of ileal pH.

Urinary excretion of magnesium and calcium as an index of absorption is not affected by lactose intake in healthy adults.

The effect of lactose on the urinary excretion of Mg and Ca, as an index of absorption, was studied in a double-blind, crossover study during three 1-week periods. Twenty-four healthy, lactose-tolerant, adult volunteers maintained their habitual diets with the exception that all lactose-containing dairy products in the diet were replaced by 600 g/d of three specially prepared dairy products. These products were based on either lactose-enriched cow's milk or lactose-enriched, lactase (EC 3.2.1.23)-treated cow's milk, with or without added Mg, and were given in turn during 1 week. Lactose intake was increased by 127 mmol/d (46 g/d) while taking the lactose-enriched products. While taking the Mg-enriched products, Mg intake was increased by 2.8 mmol/d (69 mg/d) which was equivalent to 17% of the habitual Mg intake. Apart from the lactose and Mg intake, nutrient intake was comparable during the three dietary periods. Urinary excretions of Mg and Ca were used as indicators for their absorption. Mg supplementation significantly increased urinary Mg excretion by 0.97 mmol/d (equivalent to an increase of 18%, P < 0.001), indicating that urinary Mg excretion is a valid indicator for intestinal Mg absorption. Hydrolysis of lactose did not affect urinary excretion of Mg and Ca, which implies that lactose intake does not affect the absorption of Mg and Ca in healthy adults.

Inhibitory effect of soybean protein vs. casein on apparent absorption of magnesium in rats is due to greater excretion of endogenous magnesium.

Apparent magnesium absorption is depressed in rats fed diets containing soybean protein or enriched with sodium phytate or phosphate in comparison with casein, whereas it is raised in rats fed lactose. However, the possibility that changes in apparent absorption are caused by changes in fecal excretion of endogenous magnesium cannot be excluded. We studied the effects of casein, soybean protein, sodium phytate, lactose and phosphate on apparent and true absorption of magnesium. True magnesium absorption was measured with the use of oral and intraperitoneal administration of tracer doses of 28Mg. Fecal excretion of endogenous magnesium was calculated from apparent and true absorption. True magnesium absorption was not affected by either substitution of soybean protein for casein or by the addition of sodium phytate to a diet containing casein. Endogenous magnesium excretion in feces was significantly increased by soybean protein and sodium phytate. Thus the observed impairment of apparent magnesium absorption in rats fed soybean protein or sodium phytate is due to enhanced fecal excretion of endogenous magnesium. With the other dietary treatments, enhanced fecal excretion of endogenous magnesium was not associated with a discrepancy in the effects on apparent and true magnesium absorption. Dietary lactose vs. dextrose and supplemental phosphate both stimulated fecal excretion of endogenous magnesium, but lactose raised both true and apparent magnesium absorption, and phosphate depressed both true and apparent magnesium absorption.

Bioavailability of magnesium and calcium from cow's milk and soya-bean beverage in rats.

The milk components lactose and casein enhance the apparent absorption of magnesium and possibly also of calcium, whereas phytate, which occurs in soya-bean products, has an inhibitory effect. This implies that soya-bean beverage v. cow's milk could lower bioavailability of Mg and Ca. This hypothesis was tested in two experiments with growing rats. Feeding soya-bean beverage v. cow's milk consistently lowered body-weight gain, enhanced bone turnover, as measured by increased plasma alkaline phosphatase (EC 3.1.3.1) activity and increased urinary hydroxyproline excretion, and decreased Mg and Ca concentrations in the femur. Because the mineral compositions of the soya-bean beverage and the cow's milk were different, the intake of Mg was higher in rats fed on soya-bean beverage, whereas that of Ca was higher in rats fed on cow's milk. Supplementation of the soya-bean beverage either with phosphorus and Ca or with P, Ca and methionine, to concentrations identical to those in milk, restored growth and bone mineralization. When using diets carefully balanced for Mg, Ca, P, sodium, potassium and methionine, soya-bean beverage v. cow's milk in the diets decreased apparent absorption and urinary excretion of Mg and Ca. Hydrolysis of lactose in milk decreased absorption and urinary excretion of Mg; it did not significantly affect Ca absorption but lowered urinary Ca excretion. The present study shows that soya-bean beverage v. milk depresses Mg and Ca bioavailability, as would be predicted on the basis of reported effects of their purified components.

Interaction of calcium and phosphate decreases ileal magnesium solubility and apparent magnesium absorption in rats.

We tested the hypothesis that increased intakes of calcium and phosphate lower magnesium solubility in the intestinal lumen, causing a decreased magnesium absorption. In in vitro experiments at a constant magnesium concentration, increasing calcium concentrations reduced magnesium solubility. This effect did not occur in the absence of phosphate. Increasing phosphate concentrations decreased the solubility of magnesium in the presence, but not in the absence, of calcium. These results suggest that the formation of an insoluble calcium-magnesium-phosphate complex determines magnesium solubility. To extend this concept to in vivo conditions, rats were fed purified diets containing a constant concentration of magnesium (16.4 mumol/g) but different concentrations of calcium (25, 100 or 175 mumol/g) and phosphate (58, 103 or 161 mumol/g). Increased intakes of calcium decreased magnesium solubility in the ileal lumen and lowered magnesium absorption. The latter result occurred only if the dietary phosphate concentration was at least 103 mumol/g. Increasing dietary phosphate concentrations reduced both magnesium solubility in the ileum and magnesium absorption, but only if the dietary calcium concentration was at least 100 mumol/g. These results support those obtained in vitro. We conclude that increased intakes of calcium and phosphate decrease magnesium absorption by the formation of an insoluble calcium-magnesium-phosphate complex in the intestinal lumen.

Nutrition and magnesium absorption: a review.

This paper reviews the evidence that certain dietary components can affect intestinal absorption of magnesium. Increased intakes of protein and fructose improve apparent magnesium absorption (magnesium intake minus fecal excretion) in humans, whereas a lowering effect occurs with consumption of cellulose and phytate. Although dietary concentrations of lactose, fat, calcium and phosphate have clear effects on magnesium absorption in experiments with rats, the impact of these nutrients on magnesium absorption in humans remains unsettled. Mechanisms underlying the effects of dietary components on magnesium absorption in humans are generally poorly understood. A change in magnesium absorption not necessarily results in a change in magnesium retention. When consuming practical diets, the fall of apparent magnesium absorption caused by phytate and cellulose is generally compensated by increased magnesium intake due to high magnesium concentrations in phytate- and cellulose-rich products. Furthermore, to maintain homeostasis, urinary magnesium excretion will be raised after stimulation of apparent magnesium absorption and it will be lowered after impairment of apparent magnesium absorption. Thus, the effects of dietary components on magnesium absorption probably are critically important only at low intakes of magnesium. At low magnesium intakes, differences in magnesium absorption may be expected to influence magnesium retention and thus can either induce or abolish magnesium deficiency.

Inhibitory effect of dietary soybean protein vs. casein on magnesium absorption in rats.

The effects of casein and soybean protein on magnesium absorption and magnesium concentration in the femur were investigated in rats. Purified diets containing either casein or soybean protein and three concentrations of added magnesium (0.82, 1.64 or 2.46 mmol/100 g diet) were used. The isonitrogenous diets were carefully balanced for the different mineral concentrations in the protein preparations. Absolute and percent magnesium absorption and urinary magnesium excretion were significantly decreased in rats fed soybean protein when compared with casein, irrespective of the dietary concentration of added magnesium. The magnesium content of femur was significantly lower in rats fed soybean protein, but this effect was seen only when the diet contained 0.82 mmol magnesium/100 g diet. The addition of sodium phytate to the casein diets, to a concentration identical to that in the diets containing soybean protein as provided by the soybean protein preparation, produced similar effects on magnesium absorption as the diets containing soybean protein. These results indicate that soybean protein, when compared with casein, decreases magnesium absorption through its phytate component.

A co-cultivation system as a model for in vitro studies of modulating effects of naturally occurring indoles on the genotoxicity of model compounds.

An in vitro model system, consisting of primary chick embryo hepatocytes as the metabolizing system co-cultured with V79 Chinese hamster cells as the target cells for the SCE assay, was used to study the modulating effects of naturally occurring indoles on the genotoxicity of benzo[a]pyrene (B[a]P) and N-nitrosodimethylamine (NDMA). At 25 mug/ml, indole-3-carbinol (I3C) induced ethoxyresorufin-O-deethylase (ERROD) activity 3.9-fold and ethoxycoumarin-O-deethylase (ETCO) activity 2-fold. Indole-3-acetonitrile (I3A; 35 mug/ml) induced ERROD activity 1.6-fold and ETCO activity 2-fold. Pretreatment with I3C resulted in a 20-40% decrease in genotoxicity for both B[a]P and NDMA. Pretreatment with I3A resulted in a similar decrease in genotoxicity for B[a]P, whereas no decrease was observed for NDMA. When a microsomal fraction prepared from I3C-pretreated hepatocytes was used, no decrease in B[a]P-induced genotoxicity was found; in contrast, use of an S-9 fraction prepared from the same cells resulted in a 45% decrease. Exposure of cells to B[a]P after pretreatment with I3C for suboptimal times also resulted in a significant decrease in genotoxic activity. The data indicate that the protective effects of pretreatment with the indoles, observed in this study, are not directly correlated with induction of cytochrome P-450-associated enzymes. Instead they seem to be more the result of a changed balance in the enzyme systems involved in the indole biotransformation process and point to an essential role of conjugating enzyme systems.