Impact of energy and casein or whey protein intake on bone status in a rat model of age-related bone loss.

In the elderly, nutritional deficiencies, such as low energy and protein intake, are suggested to increase the risk of osteoporotic fractures. Modulation of the amount and quality of protein intake under energy deficient conditions represents an interesting strategy to prevent aged-related bone loss. We investigated the effect of a 5-month dietary restriction on bone status in 16-month-old male rats. Rats were randomised into six groups (n 10 per group). Control animals were fed a normal diet containing either casein (N-C) or whey protein (N-WP). The other groups received a 40 % protein and energy-restricted diet with casein or whey protein (PER-C and PER-WP) or a normal protein and energy-restricted diet (ER-C and ER-WP). Both restrictions (PER and ER) induced a decrease in femoral bone mineral density (BMD), consistent with impaired biomechanical properties and a reduced cortical area at the diaphysis. Plasma osteocalcin and urinary deoxypyridinoline levels suggested a decrease in bone turnover in the PER and ER groups. Interestingly, circulating insulin-like growth factor 1 (IGF-1) levels were also lowered. Overall, normal protein intake did not elicit any bone sparing effect in energy-deficient rats. Regarding protein quality, neither casein nor WP appeared to significantly prevent the BMD decrease. This study confirms that nutritional deficiencies may contribute to osteopenia through decreased IGF-1 levels. Moreover, it seems that impaired bone status could not be significantly prevented by modulating the amount and quality of dietary proteins.

Restoration of thiamine status with white or whole wheat bread in a thiamine-depleted rat model.

Long-term thiamine deficiency has been largely documented, whilst little is known about effects of short-term depletion/repletion periods on thiamine vitamers status. Rats were submitted to short-term depletion (8 days) followed by different durations of repletion (3 or 14 days) with thiamine from bread (whole wheat bread or white bread, whole B and white B respectively) or corresponding controls. Short-term depletion drastically decreased plasma thiamine (-97%) and its urinary excretion (-77%). TDP (thiamine diphosphate) was strongly affected in liver (-67%) but less affected in cerebellum (-38%) or kidneys (-45%). Short-term repletion (3 days) with whole B diet or its control restored TDP at initial values in cerebellum and kidneys. A longer repletion (14 days) was required to restore liver TDP. Comparison of the diet groups indicates that thiamine status in tissues of rat fed whole B or white B diet was comparable to that of rats fed purified thiamine. Plasma thiamine concentration could not be restored at initial values in the bread groups or respective controls. In conclusion, thiamine in whole wheat bread appears effective in preventing marginal deficiencies and plasma thiamine is a less reliable indicator of thiamine status than tissue TDP levels.

Determination of thiamine and its phosphate esters in rat tissues analyzed as thiochromes on a RP-amide C16 column.

A new reversed-phase chromatographic method is described for the separation and quantification of thiamine (T), thiamine monophosphate (TMP) and diphosphate (TDP) in rat tissues. Sample extraction with perchloric acid (HClO(4)) was found more suitable than extraction with trichloroacetic acid (TCA), as regards convenience and background fluorescence. Derivatization of thiamine vitamers to thiochromes was optimized and complete separation of TDP and TMP thiochromes was obtained on a RP-amide C16 column in isocratic elution, with T thiochrome eluting in less than 10 min. The precision and the accuracy of the HPLC procedure were assessed: ranging from 0.5 to 7.7% for intra-day and from 2.0 to 9.4% for inter-day precision, a recovery average of 101% was determined (range 90-111%). Mean values of recovery for TDP, TMP or T were 91, 96 and 90% for liver extracts, respectively. Analysis of vitamers in tissues of rat submitted to 8 days thiamin deficiency, followed by a 14 days repletion, showed a significant reduction of TPP after 8 days of depletion in liver (-67%), brains (-50%), kidneys (-60%), followed by a complete recovery upon repletion.

Bioavailability of phloretin and phloridzin in rats.

Phloretin is a flavonoid found exclusively in apples and in apple-derived products where it is present as the glucosidic form, namely, phloridzin (phloretin 2'-O-glucose). In the present study, we compared the changes in plasma and urine concentrations of these two compounds in rats fed a single meal containing 0.25% phloridzin or 0.157% phloretin (corresponding to the ingestion of 22 mg of phloretin equivalents). In plasma, phloretin was recovered mainly as the conjugated forms (glucuronided and/or sulfated) but some unconjugated phloretin was also detected. By contrast, no trace of intact phloridzin was detected in plasma of rats fed a phloridzin meal. These compounds presented different kinetics of absorption; phloretin appeared more rapidly in plasma when rats were fed the aglycone than when fed the glucoside. However, whatever compound was administered, no significant difference in the plasma concentrations of total phloretin were observed 10 h after food intake. At 24 h after the beginning of the meal, the plasma concentrations of phloretin were almost back to the baseline, indicating that this compound was excreted rapidly in urine. The total urinary excretion rate of phloretin was not affected by the forms administered, and was estimated to be 8.5 micromol/24 h in rats fed phloretin or phloridzin. Thus, 10.4% of the ingested dose was recovered in urine after 24 h.

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.

Comparison of the intestinal absorption of quercetin, phloretin and their glucosides in rats.

Absorption and metabolism of quercetin and isoquercitrin (quercetin 3-O-glucose) were investigated in rats after in situ perfusion of jejunum plus ileum (15 nmol/min) for 30 min and compared with those of phloretin and phloridzin (phloretin 2'-O-glucose). After perfusion of the glucosides, the corresponding aglycone forms and conjugated derivatives appeared in the lumen. The conjugated metabolites were similar to those recovered after intestinal perfusion of the aglycone forms. Regardless of the aglycone or glucoside perfused, only conjugated forms were present in the mesenteric vein blood draining the perfused segment showing the importance of intestinal conjugation. The hydrolysis of glucosides was a prerequisite step before their conjugation by intestinal enzymes and their transport towards the mucosal and serosal sides. In contrast to phloridzin, lactase phloridzin hydrolase activity did not seem to be an essential pathway for isoquercitrin hydrolysis. The 3-O-glucosylation of quercetin improved the net absorption of the aglycone (P < 0.05), whereas phloretin absorption decreased when present as 2'-O-glucoside (P < 0.05). Whatever the perfused compound, the efficiency of the absorption seemed to be linked to the intestinal conjugation process and to the luminal secretion of metabolites.

Whole wheat and triticale flours with differing viscosities stimulate cecal fermentations and lower plasma and hepatic lipids in rats.

Whole flours from oat, rye or barley effectively modify digestive fermentation and lipid metabolism, whereas the effectiveness of whole wheat flour has not been established. To address this question, cecal digestion, short-chain fatty acid (SCFA) metabolism and cholesterol metabolism were investigated in four groups of rats fed the following semipurified diets differing in their carbohydrate source: a control diet (purified wheat starch) and three whole cereal flour diets [Valoris wheat (Wv), Soissons wheat (Ws), or Carnac triticale (Tc)]. Wv is particularly viscous and rich in arabinoxylans, and Tc is richer in hemicellulose than wheat. Compared with controls, rats fed the whole-flour diets had enlarged ceca and a moderate acidification of the bulk pH ( approximately 6.4). In these rats, the cecal SCFA pool size was enhanced (P < 0.05), and the SCFA molar ratio reflected propionic/butyric acid-rich fermentations, especially in those fed TC: The portal SCFA concentrations reflected the rise of the acetic and propionic acid pools in the cecum, whereas portal butyric acid remained relatively low, probably reflecting extensive metabolism by the cecal wall. The fecal excretion of total steroids (bile acids + sterols) was markedly enhanced by all of the whole-flour diets, with Wv (+78%) > Tc (+64%) > Ws (+47%). In parallel, there was a significant plasma cholesterol-lowering effect for rats fed Wv (-27%) and Tc (-32%) and a plasma triglyceride-lowering effect (approximately -40%) in all rats fed whole-flour diets (P < 0.05). This effect was observed mainly for triglyceride-rich lipoprotein-cholesterol, whereas HDL cholesterol was unaffected. These results indicate that whole wheat flours can strikingly affect cecal SCFA, especially butyrate, and are effective plasma cholesterol-lowering agents.

Prolonged fermentation of whole wheat sourdough reduces phytate level and increases soluble magnesium.

This work was designed to compare the effects of different leavens (yeast, sourdough, and a mixture of both) on phytic acid (PA) degradation and to assess the repercussions of PA breakdown on phosphorus and magnesium solubility during bread-making. Sourdough fermentation was more efficient than yeast fermentation in reducing the phytate content in whole wheat bread (-62 and -38%, respectively). Furthermore, lactic acid bacteria present in sourdough enhanced acidification, leading to increased magnesium and phosphorus solubility. To intensify phytate breakdown, bran was incubated with microorganisms (yeast or sourdough) before bread-making. Using this new method, the percentage of phytate breakdown was near 90%, whereas 40% of phytate remained in traditional French bread. In conclusion, a prolonged fermentation with sourdough still leads to improved Mg and P solubility by decreasing phytate content and through acidification.

Class 2 resistant starches lower plasma and liver lipids and improve mineral retention in rats.

The effects of raw potato starch (RPS) and high amylose corn starch (HAS) on cecal digestion, lipid metabolism and mineral utilization (Ca and Mg) were compared in rats adapted to semipurified diets. The diets provided either 710 g wheat starch/100 g diet (control) alone or 510 g wheat starch/100 g diet plus 200 g resistant starch/100 g (RPS or HAS). Compared with rats fed the control diet, significant cecal hypertrophy (240% after 7 d of the fiber consumption) and short-chain fatty acids accumulation (especially propionic and butyric acids) occurred after both resistant starch diets. Apparent Ca, Mg, Zn, Fe and Cu absorptions were similarly enhanced by RPS and HAS (50, 50, 27, 21 and 90%, respectively). Cholesterol absorption was reduced to 14% of intake in rats fed RPS or HAS compared with 47% absorption in control rats. RPS and HAS were also effective in lowering plasma cholesterol (-31 and -27%, respectively) and triglycerides (-28 and -22%, respectively). There was no effect of the diets on cholesterol in d > 1.040 kg/L lipoproteins (HDL), whereas RPS and HAS depressed cholesterol in d < 1.040 kg/L lipoproteins (especially in triglyceride-rich lipoproteins). Moreover, there were lower concentrations of cholesterol (-50 and -40%, respectively) and triglycerides (-53 and -47%, respectively) in the livers of RPS- and HAS-fed rats. Thus, RPS and HAS have similar effects on intestinal fermentation, mineral utilization and cholesterol metabolism in rats.

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.

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.

[Nutrition and prostatic cancer]. / Nutrition et cancer de prostate.

Due to the major geographical variations affecting its clinical incidence, prostate cancer appears to be influenced by environmental factors, which may either promote or inhibit the development of this tumour. Diet appears to play a considerable role among these environmental factors. There are epidemiological and experimental arguments in favour of the role of diet in the development of prostatic cancer. Certain foods, such as fats, phenolic compound and other micronutrients such as vitamins or selenium have been reported to have an action on the natural history of prostate cancer. The authors present a review of the literature analysing the various potential actions of various foods.

Dietary phytic acid and wheat bran enhance mucosal phytase activity in rat small intestine.

The aim of this work was to investigate the influence of dietary phytic acid (PA) on intestinal phytase activity in growing rats by in vitro determination of phytase activity in the three segments of the small intestine (duodenum, jejunum and ileum), and by in vivo intestinal perfusion of a solution rich in PA (diluted soymilk). Using the in vitro method, duodenal and jejunal activities were enhanced significantly by adaptation to purified PA (+44 and +145% respectively, compared with control rats). For the rats adapted to the wheat bran (WB) diet, the induction of intestinal phytase by the substrate compared with the control values (P < 0.001) was observed only in ileum. Using soymilk in perfusions, rats consuming PA or WB diets hydrolyzed more phytate (P < 0.001 and P < 0.05, respectively) than controls. Further, Mg absorption from diluted soymilk was not affected by food adaptation, whereas Ca absorption was greater in the PA and WB groups (P < 0.001 and P < 0.05, respectively) than in the control group. Thus, intake of pure PA by rats enhances phytase in the upper parts of the small intestine (duodenum and jejunum), whereas the WB diet activates ileal phytase. Furthermore, the induction of phytase activity is greater in magnitude in rats fed synthetic PA than that observed in rats fed the WB diet. The enhancement of phytase improves intestinal Ca absorption, thus showing the capacity of the small intestine to adapt to diets rich in PA and poor in Ca.

Strains of lactic acid bacteria isolated from sour doughs degrade phytic acid and improve calcium and magnesium solubility from whole wheat flour.

Five strains of lactic bacteria have been isolated from sour doughs and examined for their ability to degrade phytic acid. In white flour medium in which phytic acid was the only source of phosphorus, the disappearance of phytate and an elevation of inorganic phosphate were observed after only 2 h of incubation in all strains tested (-30 and +60%, respectively). Both phenomena correspond to phytate breakdown. No difference was observed in the levels of phytic acid hydrolysis among strains, suggesting that phytase enzymes are similar among these bacteria. Using whole wheat flour medium naturally rich in phytic acid in the presence of Leuconostoc mesenteroides strain 38, a 9 h fermentation established that the degradation of PA and the production of lactic acid lead to greater Ca and Mg solubility than in control medium.

Cholesterol-lowering effects of guar gum: changes in bile acid pools and intestinal reabsorption.

Soluble fibers such as guar gum (GG) may exert cholesterol-lowering effects. It is generally accepted that bile acid (BA) reabsorption in portal blood is reduced, thus limiting the capacity of BA to down-regulate liver cholesterol 7alpha-hydroxylase, the rate-limiting enzyme of BA synthesis. In the present work, rats were adapted to fiber-free (FF) or 5% GG diets (supplemented or not with 0.25% cholesterol), to investigate various aspects of enterohepatic BA cycling. GG in the diet at a level of 5% elicited a significant lowering of plasma cholesterol during the absorptive period, in cholesterol-free (-13%) or 0.25% cholesterol (-20%) diet conditions. In rats adapted to the GG diets, the small intestinal and cecal BA pools and the ileal vein-artery difference for BA were markedly enhanced; reabsorption in the cecal vein was also enhanced in these rats. [14C]Taurocholate absorption, determined in perfused ileal segments, was not significantly different in rats adapted to the FF or GG diet, suggesting that a greater flux of BA in the ileum might support a greater ileal BA reabsorption in rats adapted to the GG diet. In contrast, capacities for [14C]cholate absorption from the cecum at pH 6.5 were higher in rats adapted to the GG diet than to the FF diet. Acidification of the bulk medium in isolated cecum (from pH 7.1 down to pH 6.5 or 5.8) or addition of 100 mM volatile fatty acids was also found to stimulate cecal [14C]cholate absorption. These factors could contribute to accelerated cecal BA absorption in rats fed the GG diet. The effects of GG on steroid fecal excretion thus appear to accompany a greater intestinal BA absorption and portal flux to the liver. These results suggest that some mechanisms invoked to explain cholesterol-lowering effect of fibers should be reconsidered.

Low levels of viscous hydrocolloids lower plasma cholesterol in rats primarily by impairing cholesterol absorption.

Hydrocolloids have been proposed as cholesterol-lowering agents, but their viscosity limits their use in human nutrition. A low level (1 %) of hydrocolloids (guar gum, (GG); xanthan gum, (XG); and konjac mannan) was investigated in rats fed 0.2 g/100 g cholesterol diets. Food intake and body weight gain were not altered by the diets. Bile flow and cholesterol bile flux were not modified by diet, whereas the bile acid flux was greater in rats fed hydrocolloid diets. The cecal pool of bile acids was greater than control rats only in rats fed the XG diet (+71%, P<0.001). The fecal excretion of neutral sterols was stimulated in rats fed the hydrocolloid diets; cholesterol apparent digestibility (60% in controls) was reduced to 30-36% in rats fed hydrocolloids. Bile acid fecal excretion was not altered by diet treatment. As a result, apparent steroid balance was about +40 micromol/d in controls and only +10 to +20 micromol/d in rats fed hydrocolloids. Both plasma cholesterol and triglycerides were significantly lower than controls in rats fed XG, but only cholesterol was lower in rats fed the GG diet. These effects were essentially found in the d <1.040 kg/L fraction. Liver cholesterol content was significantly lower than in controls in rats fed the GG or XG diets. Liver HMG CoA reductase was not affected by the hydrocolloid diets. In conclusion, a low percentage of viscous hydrocolloids lowers plasma cholesterol in cholesterol-fed rats. Inhibition of intestinal cholesterol absorption may be the primary mechanism.

Part of quercetin absorbed in the small intestine is conjugated and further secreted in the intestinal lumen.

Rutin and quercetin absorption and metabolism were investigated in rats after in situ perfusion of jejunum plus ileum (15 nmol/min). In contrast to rutin, a high proportion of quercetin (two-thirds) disappeared during perfusion, reflecting extensive transfer into the intestinal wall. Net quercetin absorption was not complete (2.1 nmol/min), inasmuch as 52% were reexcreted in the lumen as conjugated derivatives (7.7 nmol/min). Enterohepatic recycling contribution of flavonoids was excluded by catheterization of the biliary duct before perfusion. After a 30-min perfusion period, 0.71 microM of quercetin equivalents were detected in plasma, reflecting a significant absorption from the small intestine. The differential hydrolysis of effluent samples by glucuronidase and/or sulfatase indicates that the conjugated forms released in the lumen were 1) glucuronidated derivatives of quercetin and of its methoxylated forms (64%) and 2) sulfated form of quercetin (36%). In vitro quercetin glucuronides synthetized using jejunal and ileal microsomal fractions were similar to those recovered in the effluent of perfusion. These data suggest that glucuronidation and sulfatation take place in intestinal cells, whereas no glucurono-sulfoconjugates could be detected in the effluent. The present work shows that a rapid quercetin absorption in the small intestine is very effective together with its active conjugation in intestinal cells.

Role of fermentable carbohydrate supplements with a low-protein diet in the course of chronic renal failure: experimental bases.

During the past few years, considerable attention has been given to the impact of nutrition on kidney disease. The question arises of whether the effect of a moderate dietary protein restriction could be reinforced by enrichment of the diet with fermentable carbohydrates. Feeding fermentable carbohydrates may stimulate the extrarenal route of nitrogen (N) excretion through the fecal route. Such an effect has been reported in several species, including healthy humans and patients with chronic renal failure (CRF). Furthermore, studies of these subjects show that the greater fecal N excretion during the fermentable carbohydrate supplementation period was accompanied by a significant decrease in plasma urea concentration. In animal models of experimental renal failure, the consumption of diets containing fermentable carbohydrates results in a greater rate of urea N transfer from blood to the cecal lumen, where it is hydrolyzed by bacterial urease before subsequent microflora metabolism and proliferation. Therefore, this results in a greater fecal N excretion, coupled with a reduction in urinary N excretion and plasma urea concentration. Because elevated concentrations of serum urea N have been associated with adverse clinical symptoms of CRF, these results suggest a possible usefulness of combining fermentable carbohydrates with a low-protein diet to increase N excretion through the fecal route. Further investigations in this population of patients of whether fermentable carbohydrates in the diet may be beneficial in delaying or treating the symptoms and chronic complications of CRF will certainly emerge in the future. This should be realized without adversely affecting nutritional status and, as far as possible, by optimizing protein intake for the patients without being detrimental to renal function.

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.

Comparison of the bioavailability of quercetin and catechin in rats.

Quercetin and catechin are present in noticeable amounts in human diet and these polyphenolic compounds are supposed to exert beneficial effects on human health. However, their metabolic fates in the organism have never been compared. In the present study, rats were fed a 0.25% quercetin or a 0.25% catechin diet. Quercetin and catechin metabolites were analyzed in plasma and liver samples by high-performance liquid chromatography coupled to an ultraviolet or a multielectrode coulometric detection. All plasma metabolites were present as conjugated forms, but catechin metabolites were mainly constituted by glucuronidated derivatives, whereas quercetin metabolites were sulfo- and glucurono-sulfo conjugates. Quercetin was more intensively methylated than catechin in plasma. The plasma quercetin metabolites are well maintained during the postabsorptive period (approximately 50 microM), whereas the concentration of catechin metabolites dropped dramatically between 12- and 24-h after an experimental meal (from 38.0 to 4.5 microM). In the liver, the concentrations of quercetin and catechin derivatives were lower than in plasma, and no accumulation was observed when the rats were adapted for 14 d to the supplemented diets. The hepatic metabolites were intensively methylated (90-95%), but in contrast to plasma, some free aglycones could be detected. Thus, it clearly appears that studies dealing with the biological impact of these polyphenols should take into account the feature of their bioavailability, particularly the fact that their circulating metabolites are conjugated derivatives.