Hassan Younes

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.

Acidic fermentation in the caecum increases absorption of calcium and magnesium in the large intestine of the rat

The effect of fermentation on colonic absorption of Ca and Mg was investigated in 8-week-old rats adapted to diets containing either digestible wheat starch (DS diets) or including resistant starch, i.e. 350 g raw potato starch/kg (RS diets). The dietary Ca level of the DS and RS diets was 2.5 or 7.5 g/kg. RS diets resulted in enlargements of the caecum together with hypertrophy of the caecal wall. Acidification of the caecal contents by microbial fermentation of RS was influenced by the dietary Ca level. Very acidic pH conditions and relatively low concentrations of short-chain fatty acids, in the presence of lactic acid fermentation, were observed with the 2.5 g Ca/kg level. Rats fed on RS diets had a higher percentage of soluble Ca (and inorganic phosphate) in the caecum, particularly of rats adapted to the high Ca level. As a result of the hypertrophy of the caecal wall and of an elevated concentration of soluble Ca, the caecal absorption of Ca was 5-6-fold higher in the RS groups than in the DS groups. The difference between dietary intake and faecal excretion (DI-FE) of Ca was higher in rats fed on RS diets than in those fed on DS diets, when the dietary Ca level was 2.5 g/kg. With the higher Ca intake the elevated rate of Ca absorption from the caecum in RS-fed rats was not paralleled by an enhanced DI-EE difference: this suggests a shift of the Ca absorption towards the large intestine. Feeding RS diets also enhanced Mg caecal absorption, resulting in a substantially higher DI-FE difference for Mg, especially with the 2.5 g Ca/kg diets, because a high Ca intake tends to inhibit Mg absorption. The present findings support the view that the large intestine may represent a major site of Ca (and Mg) absorption when acidic fermentations take place. This process could improve the digestive Ca balance when the dietary Ca supply is low; when the Ca supply is affluent, it rather shifts Ca absorption towards a more distal site of the digestive tract.

Xylo-oligosaccharide (XOS) in combination with inulin modulates both the intestinal environment and immune status in healthy subjects, while XOS alone only shows prebiotic properties

The purpose of the present study was to establish the prebiotic effect of a new xylo-oligosaccharide (XOS) and of an inulin-and-XOS mixture (INU-XOS) and to determine their effect on endotoxaemia (lipopolysaccharides (LPS)) and immune parameters. In this randomised, parallel, placebo-controlled, double-blind study, sixty healthy volunteers were randomly assigned to three groups, receiving either 5 g XOS, INU-XOS (3 g inulin +1 g XOS) or an equivalent weight of wheat maltodextrin (placebo) during 4 weeks. Faecal samples were collected to assess the effects of these products on microbiota, as well as SCFA composition, enzymatic activities and secretory IgA production. Circulating LPS was measured in plasma samples, and whole blood was incubated with LPS to measure cytokine expression. Consumption of XOS alone increased the faecal concentrations of Bifidobacterium and butyrate and activities of α-glucosidase and β-glucuronidase, while decreasing the concentrations of acetate and p-cresol. Consumption of XOS in combination with inulin did not decrease the concentrations of acetate and p-cresol, but increased in addition the faecal concentrations of total SCFA and propionate. Furthermore, consumption of XOS in combination with inulin decreased LPS concentrations in blood and attenuated LPS-induced increases in gene expression in IL-1β and LPS-induced decreases in gene expression in IL-13 in blood. In conclusion, consumption of XOS alone or in combination with inulin results in beneficial albeit different changes in the intestinal microbiome on a high-fat diet. In addition, consumption of XOS in combination with inulin attenuates the proinflammatory effects of a high-fat diet in the blood of healthy subjects.

Resistant starch is more effective than cholestyramine as a lipid-lowering agent in the rat.

Amylase-resistant starch (RS) represents a substrate for the bacterial flora of the colon, and the question arises as whether RS shares with soluble fibers common mechanisms for their lipid-lowering effects. It is uncertain whether a cholesterol-lowering effect depends basically on an enhanced rate of steroid excretion or whether colonic fermentations also play a role in this effect. In the present study, the effect of RS (25% raw potato starch), of a steroid sequestrant (0.8% cholestyramine), or both were compared on bile acid excretion and lipid metabolism in rats fed semipurified diets. RS diets led to a marked rise in cecal size and the cecal pool of short-chain fatty acids (SCFA), as well as SCFA absorption; cholestyramine did not noticeably affect cecal fermentation. Whereas cholestyramine was particularly effective at enhancing bile acid excretion, RS was more effective in lowering plasma cholesterol (−32%) and triglycerides (−29%). The activity of 3-hydroxy-3-methylglutaryl-CoA reductase was increased fivefold by cholestyramine and twofold by RS. This induction in rats fed RS diets was concomittant to a depressed fatty acid synthase activity. In rats fed the RS diet, there was a lower concentration of cholesterol in all lipoprotein fractions, especially the (d=1.040−1.080) fraction high-density lipoprotein (HDL1), while those fed cholestyramine had only a significant reduction of HDL1 cholesterol. In contrast to cholestyramine, RS also depressed the concentration of triglycerides in the triglyceride-rich lipoprotein fraction. There was no noticeable synergy between the effects of RS and cholestyramine when both were present in the diet. This suggests that the cholesterol-lowering effect of RS is not limited to its capacity to enhance bile acids excretion. The difference between RS and cholestyramine could relate to the capacity of fermentation end-products to counteract the upregulation of cholesterol and bile acid biosynthesis. Thus, in the absence of fermentation in the large intestine, a high rate of bile acids excretion is not always sufficient to elicit a cholesterol-lowering effect.

Resistant starch exerts a lowering effect on plasma urea by enhancing urea N transfer into the large intestine

Abstract Fermentable polysaccharides may have interesting effects in the large intestine, on urea N disposal and N fecal excretion. To further investigate this domain, rats were adapted to diets containing only digestible starch (DS) or in which a part of the starch was replaced by resistant starch (RS) (crude potato starch, 250g/Kg), the dietary protein level being either 130 or 260g casein/Kg. Feeding RS led to an hypertrophy of the cecum and a high concentration of short-chain fatty acids (SCFA) at acidic pH. 25% RS in the diet resulted in an elevated rate of urea N transfer and retention in the cecum. Plasma urea influenced the quantity of urea N entering the cecum and the extent of ammonia N cycling; however, the quantities of N retained in cecum were not significantly increased. In rats fed RS diets, the cecal ammonia remained at low concentrations, whereas the total cecal nitrogen was 3-fold enhanced. The increase of fecal N excretion by RS diets was probably the result of an accelerated rate of bacterial protein synthesis. The shift of N elimination towards urea N transfer into the large intestine was particularly effective in rats fed 130g casein/Kg diet: the N excretion by the fecal route being then of the same magnitude as urinary excretion. The urea lowering effect of RS was more pronounced when rats were fed a moderate casein level; thus, by manipulating dietary supply of protein and fermentable carbohydrates it could be possible to noticeably depress the quantities of N to be eliminated by the kidneys.

Effectiveness of resistant starch, compared to guar gum, in depressing plasma cholesterol and enhancing fecal steroid excretion

Amylase-resistant starch (RS) represents a substrate that can be administered in substantial amounts in the diet, in contrast to gel-forming polysaccharides, such as guar gum (GG). The aim of this work was thus to compare the effects of GG and RS on cholesterol metabolism in rats adapted to 0.4% cholesterol diets, using dietary GG or RS levels (8 or 20%, respectively) that led to a similar development of fermentations, as assessed by the degree of enlargement of the cecum. The RS diet elicited a marked rise in the cecal pool of short-chain fatty acids, especially acetic and butyric acid, whereas the GG diet favored high-propionic acid fermentations. Both polysaccharides markedly altered the cholesterol excretion, from 50% of ingested cholesterol in controls, up to about 70% in rats adapted to the RS or GG diets. With these diets, the fecal excretion of bile acids was enhanced (67 and 144% with the RS and GG diets, respectively). RS and GG diets were effective in lowering plasma cholesterol (about −40%) and triglycerides (−36%). There was practically no effect of the diets on cholesterol in d>1.040 lipoproteins (high density lipoproteins), whereas RS (and to a larger extent, GG) were very effective to depress cholesterol in d<1.040 lipoproteins (especially in triglyceride-rich lipoproteins). Fermentable polysaccharides counteracted the accumulation of cholesterol in the liver, especially cholesterol esters. In parallel, liver acyl CoA:cholesterol acyltransferase was depressed in rats fed the RS or GG diets, whereas only the GG diet counteracted the downregulation of 3-hydroxy-3-methylglutaryl-CoA by cholesterol. These data suggest that RS may be practically as effective as a gel-forming gum, such as GG, on steroid excretion and on cholesterol metabolism.

A blend of dietary fibers increases urea disposal in the large intestine and lowers urinary nitrogen excretion in rats fed a low protein diet

Abstract The presence of rapidly fermented indigestible carbohydrates in the diet has been shown to influence intestinal fermentations and the route of excretion of urea nitrogen. The objective of the present study was to determine the effects of a dietary fiber blend on nitrogen excretion in the rat. The dietary fiber blend studied (the “oligo/fiber blend”) was comprised of 41.2% fructooligosaccharides, 17.7% insoluble oat fiber, 13.0% soy polysaccharide, 10.3% gum arabic, and 4.4% carboxymethylcellulose, which provided a diversified source of soluble and insoluble fibers. Two levels (4% and 8%) of the oligo/fiber blend were added to diets containing low (8%) and normal (14%) protein levels. Plasma urea levels were reduced by another 37% when 8% oligo/fiber was added to the low protein diet. The reduction of plasma urea levels can be explained by nitrogen metabolism in the cecum. Feeding the oligo/fiber mix elicited a bacterial proliferation characterized by short chain fatty acid production, decreased cecal pH and marked cecal hypertrophy. At the 8% oligo/fiber level, urea nitrogen uptake from blood into the cecum was increased by over 2 fold. There was a compensatory increase in ammonia nitrogen flux from gut lumen to blood at the higher oligo/fiber levels, but on balance the direction of nitrogen flux remained strongly in the direction of the cecal lumen in the oligo/fiber fed rats. As a function of total nitrogen excretion, fecal nitrogen excretion was over 80% greater in rats fed the low protein diet than in rats fed the normal protein diet. With the addition of the oligo/fiber blend, the percentage of N in the feces was increased even further. In rats fed the 8% casein/8% oligo/fiber diet, fecal N excretion was nearly the same as urinary nitrogen excretion (≈50% of total nitrogen excretion by each route). In conclusion, by decreasing dietary protein and increasing the level of a dietary fiber blend within nutritionally acceptable ranges, plasma urea was decreased and the contribution of the kidneys to nitrogen excretion would be reduced.

Relationship between Fermentations and Calcium in the Cecum of Rats Fed Digestible or Resistant Starch

The present studies were undertaken to investigate the effects of the dietary calcium (Ca) level on the Ca balance and on large intestine physiology in rats fed diets providing carbohydrate as digestible wheat starch (DS) or resistant starch (RS). Resistant starch was a high-amylose maize starch. The Ca level ranged from a marginally sufficient level (3 g/kg) to a level in excess of nutritional requirements (6 g/kg). The cecal fermentations were more developed in rats fed RS diets and they were affected by the dietary Ca level, compared to rats fed the DS diets. In rats fed a low Ca RS diet, the cecal fermentations were more acidic than with a high Ca level and there was an accumulation of lactic acid together with depressed concentrations of short-chain fatty acids. There was a considerable accumulation of Ca and phosphate (Pi) in the cecum of rats fed the 6 g/kg level; on the other hand, the concentrations of minerals (Ca, Pi) were very low in the cecum of rats fed the low Ca RS diet. The proportion of soluble Ca in the cecum was markedly enhanced by active fermentations, especially in rats fed the high Ca RS diet (16.3 mmol/l). In rats fed the RS diet, there was a substantial absorption of Ca from the cecum, which was relatively proportional to the dietary Ca level. The above data suggest that in these rats, Ca absorption in the large intestine made a substantial contribution to the digestive balance, probably at the expense of absorption in the upper part of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Dietary fiber stimulates the extra-renal route of nitrogen excretion in partially nephrectomized rats

The purpose of this study was to determine the effect of an indigestible carbohydrate/dietary fiber (the oligosaccharide/fiber blend, or O/F blend) on extra-renal nitrogen excretion in nephrectomized rats. The O/F blend provided a diversified source of soluble and insoluble fibers: 41.2% fructooligosaccharides, 26.4% insoluble oat fiber, 17.7% soy polysaccharides, 10.3% gum arabic, and 4.4% carboxymethylcellulose. Forty partially nephrectomized rats were randomized to one of four dietary treatments that varied in protein and O/F blend content. Dietary treatments were administered for 17 days (an adaptation phase of 10 days, followed by an experimental phase of 7 days) and included the following treatment groups: (1) 8% casein, 0% O/F blend, (2) 8% casein, 8% O/F blend, (3) 14% casein, 0% O/F blend, and (4) 14% casein, 8% O/F blend. Compared with nonnephrectomized normal rats (n = 10), the nephrectomy procedure induced a marked renal insufficiency, with significant increases in plasma urea and creatinine concentrations (90% and 44%, respectively). In this model of renal insufficiency, feeding the fermentable fibers had the same effect as in previous studies in normal rats: The O/F blend increased cecal weight and cecal blood flow, leading to accelerated diffusion of blood urea into the cecal lumen (by threefold), urealysis to ammonia and protein synthesis by the microflora, and increased fecal excretion of nitrogen. The efficiency of O/F blend in stimulating the extra-renal route of nitrogen excretion was greatly enhanced by the simultaneous use of a low protein rate: Fecal nitrogen excretion accounted for 23% of total nitrogen excretion in rats fed a 14% casein diet, compared with 45% in those receiving the 8% casein diet. The increase of fecal nitrogen excretion was accompanied by an equal and significant decrease in urinary nitrogen excretion and a decrease in blood urea nitrogen. In conclusion, addition of an O/F blend to a low protein diet exerts a potent urea lowering effect in renally insufficient rats, suggesting that these dietary conditions could help delay the progression of renal failure or prevent its consequences.