Dietary fibre and colonic nitrogen metabolism

Bacterial overgrowth and methane production in children with encopresis

OBJECTIVES

To assess the prevalence of small intestinal bacterial overgrowth (SIBO) and methane production in children with encopresis.

STUDY DESIGN

Radiographic fecal impaction (FI) scores were assessed in children with secondary, retentive encopresis and compared with the breath test results. Breath tests with hypoosmotic lactulose solution were performed in both the study patients (n = 50) and gastrointestinal control subjects (n = 39) groups.

RESULTS

The FI scores were significantly higher in the patients with encopresis who were methane producers (P < .01). SIBO was diagnosed in 21 of 50 (42%) patients with encopresis and 9 of 39 (23%) of control subjects (P = .06). Methane was produced in 56% of the patients with encopresis versus 23.1% of the control subjects in the gastrointestinal group (P < .01). Fasting methane level was elevated in 48% versus 10.3 %, respectively (P < .01).

CONCLUSIONS

Children with FI and encopresis had a higher prevalence of SIBO, elevated basal methane levels, and higher methane production. Methane production was associated with more severe colonic impaction. Further study is needed to determine whether methane production is a primary or secondary factor in the pathogenesis of SIBO and encopresis.

Fermentable Carbohydrate Supplementation Alters Nitrogen Excretion in Chronic Renal Failure

BACKGROUND

Considerable attention has been given to the impact of nutrition on kidney disease. Most dietary attempts to treat chronic renal failure (CRF) and to decrease uremia use a protein restriction. An alternative dietetic approach based on fermentable carbohydrate (FC) supplementation of the diet could lead to the same urea-lowering effect by increasing urea nitrogen (N) excretion in stool, with a concomitant decrease of the total N quantity excreted in urine.

METHODS

In the present prospective study, the impact of FC (40 g/d) on uremia and on N excretion routes was investigated during 5 weeks in nine CRF patients in the presence of a moderated restrictive protein diet (0.8 g/kg/d). Patients were their own controls and were treated by the cross-over method after randomization (5 weeks with FC versus 5 weeks without FC).

RESULTS

Feeding FC significantly increased the quantity of N excreted in stool from 2.1 +/- 0.8 to 3.2 +/- 1.1 g/d (+51%) (P < .01) and decreased, in parallel, the urinary N excretion from 9.4 +/- 1.7 to 8.3 +/- 1.4 g/d (-12%) (P < .01). The total N quantities excreted by the two routes were unchanged by the FC, which shows that the FC was efficient to shift N excretion from the urinary route toward the digestive route. As a result of the increase of urea transfer into the colon, the plasma urea concentration was significantly decreased from 26.1 +/- 8.7 to 20.2 +/- 8.2 mmol/L (-23%) (P < .05).

CONCLUSIONS

These results show the same beneficial effects in CRF as those obtained with a restrictive protein diet without its nutritional drawbacks. This should be confirmed by other prospective works over a longer duration and a larger number of patients to study the effects of FC on CRF progression and on CRF terminal stage tolerance.

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.

Role of intestinal bacteria in nutrient metabolism

The human large intestine contains a microbiota, the components of which are generically complex and metabolically diverse. Its primary function is to salvage energy from carbohydrate not digested in the upper gut. This is achieved through fermentation and absorption of the major products, short chain fatty acids (SCFA), which represent 40-50% of the available energy of the carbohydrate. The principal SCFA, acetate, propionate and butyrate, are metabolized by the colonic epithelium (butyrate), liver (propionate) and muscle (acetate). Intestinal bacteria also have a role in the synthesis of vitamins B and K and the metabolism of bile acids, other sterols and xenobiotics. The colonic microflora are also responsive to diet. In the presence of fermentable carbohydrate substrates such as non-starch polysaccharides, resistant starch and oligosaccharides, bacteria grow and actively synthesize protein. The amount of protein synthesis and turnover within the large intestine is difficult to determine, but around 15 g biomass is excreted in faeces each day containing 1 g bacterial-N. Whether bacterially synthesized amino acids are ever absorbed from the colon remains unclear. Finally, individual colonic micro-organisms such as sulphate-reducing bacteria, bifidobacteria and clostridia, respond selectively to specific dietary components in a way that may be important to health.

Role of intestinal bacteria in nutrient metabolism

The human large intestine contains a microbiota, the components of which are generically complex and metabolically diverse. Its primary function is to salvage energy from carbohydrate not digested in the upper gut. This is achieved through fermentation and absorption of the major products, short chain fatty acids (SCFA), which represent 40-50% of the available energy of the carbohydrate. The principal SCFA, acetate, propionate and butyrate, are metabolized by the colonic epithelium (butyrate), liver (propionate) and muscle (acetate). Intestinal bacteria also have a role in the synthesis of vitamins B and K and the metabolism of bile acids, other sterols and xenobiotics. The colonic microflora are also responsive to diet. In the presence of fermentable carbohydrate substrates such as non-starch polysaccharides, resistant starch and oligosaccharides, bacteria grow and actively synthesize protein. The amount of protein synthesis and turnover within the large intestine is difficult to determine, but around 15 g biomass is excreted in faeces each day containing 1 g bacterial-N. Whether bacterially synthesized amino acids are ever absorbed from the colon remains unclear. Finally, individual colonic micro-organisms such as sulphate-reducing bacteria, bifidobacteria and clostridia, respond selectively to specific dietary components in a way that may be important to health.

Effects of dietary fibre and tannins from apple pulp on the composition of faeces in rats

The present study was undertaken to explore the effect of apple pulp on weight and composition of faeces. This material is rich in dietary fibre (DF; 620 g dry matter/kg) and contains appreciable amounts of polyphenols. Recent reports indicate that both condensed tannins (CT) and soluble polyphenols form cross-links with protein and inhibit digestive enzymes, affecting the protein digestibility, and may produce a stimulation of endogenous nitrogen excretion. Two groups of male Wistar rats were fed on either a control diet free of DF or a diet containing 100 g apple pulp DF/kg during 7 d after a 4 d adaptation period. Body-weight and food intake were monitored daily and faeces and urine were collected once daily. DF, water content and polyphenolic compounds were measured in faeces, and N content in both faeces and urine. Faecal weight increased in the fibre group by 280 and 240% when compared with wet and dry faecal weights of animals fed on the fibre-free diet. Soluble dietary fibre (SDF) excreted in faeces was 10.9% of the SDF ingested, which suggested a low resistance to fermentation of this fraction. Of the insoluble DF, 43% of the ingested fibre was fermented. Polyphenols were degraded in the intestinal tract. Of the ingested CT, 68.6% was recovered in faeces, while the soluble polyphenols were extensively degraded (85.7% of that ingested). On the other hand, a higher faecal N excretion was observed for the fibre-fed group, suggesting a decrease in the digestibility of the dietary protein and lower apparent digestibility of the dietary protein and lower apparent digestibility and N balance indices.

Impact of dietary cereal on nutrient absorption and fecal nitrogen loss in formula-fed infants

STUDY OBJECTIVE

To determine the capacity of infants to digest and absorb rice cereal and to determine the effect of cereal feeding on total energy and nitrogen absorption.

SETTING

Subject's residences and the Texas Children's Hospital Clinical Research Center, Houston.

PATIENTS

Eight healthy 1-month-old bottle-fed infants.

INTERVENTIONS

Infants were fed their usual formula for 3 days. For the subsequent 6 days, they received 4 gm of rice cereal, labeled with carbon 13, per 30 ml of the formula.

MEASUREMENTS AND MAIN RESULTS

Fecal balance studies were performed for a 72-hour period while the infants received only formula and again during the last 3 days of cereal feeding. Breath samples for hydrogen measurement were collected before and after the cereal feeding. Nutrient intake was measured and stools were analyzed for 13C abundance, energy, nitrogen, fiber content, and bacterial mass. Cereal absorption was 88 +/- 9% (mean +/- SD). Despite a significant increase in energy and nitrogen intake from cereal feeding, the coefficient of absorption fell (energy: 97% to 90%, p = 0.048; nitrogen: 94% to 74%, p = 0.009). Fecal dry weight increased after the cereal feeding (p = 0.004), primarily as a result of a sevenfold increase in fecal bacterial mass (p = 0.002). Fecal nitrogen increased primarily because of incorporation of nitrogen into bacteria. No differences were detected in breath hydrogen as a consequence of formula feeding versus formula-cereal feeding.

CONCLUSIONS

Although cereal was relatively well-absorbed in this group of infants and increased their intakes of energy and nitrogen, it did not increase the coefficients of energy and nitrogen absorption. Cereal feeding increased fecal bacterial mass and bacterial nitrogen.