RESUMEN
Controversy exists over the contribution of dietary fiber and large bowel fermentation to human energy balance. It has been suggested that large bowel energy absorption, in the form of short-chain fatty acids, can be predicted from in vitro fermentation of human ileal digesta. Because it is difficult to obtain ileal digesta from humans with a functional large bowel to validate this approach, four normal pigs and four pigs fitted with a simple T-cannula at the distal ileum were fed a basal diet supplemented with 0, 5, 10 or 15 g pea fiber per 100 g basal diet in two parallel experiments (Latin-square design). Energy contents of diets, urine, ileal digesta and feces were determined by bomb calorimetry. Apparent total tract energy digestibility did not differ (P > 0.05) between normal and cannulated pigs. Apparent energy digestibility at the ileum decreased with increasing pea fiber intake (P < 0.05). The difference between ileal and fecal gross energy excretions in cannulated pigs was defined as large bowel energy absorption. Aliquots (0.2 g) of freeze-dried ileal digesta were fermented in vitro for 24 h with human fecal inoculum from three donors. In vitro short-chain fatty acid production was correlated with large bowel energy absorption (r = 0.90, P < 0.0001). The metabolizable energy content of pea fiber was determined to be 9.2 kJ/g pea fiber (r = 0.90, P < 0.0001) by regressing metabolizable energy retention against pea fiber intake. The integrated ileostomy-in vitro fermentation model seems to provide accurate estimates of large bowel energy absorption.
Asunto(s)
Fibras de la Dieta/metabolismo , Metabolismo Energético , Íleon/metabolismo , Animales , Fibras de la Dieta/farmacocinética , Digestión , Ácidos Grasos/biosíntesis , Fermentación , Humanos , Absorción Intestinal , Masculino , PorcinosRESUMEN
Dietary fat, protein and fibre have been shown to modulate cancer risk in humans and the present study examined the biological effects in human-flora-associated (HFA) rats of altering intake levels within the normal human range. Two control groups, one HFA and the other germfree (GF), consumed a human diet low in fat, fibre and beef for 4 weeks; three other groups consumed human diets similar except for independent 3-fold increases in fat, beef protein or fibre. After 2 weeks on the diets, magnetically recoverable microcapsules were given orally to the rats and subsequently recovered from the faeces to assess endogenous cross-linking agents. After 4 weeks, measurements were made of gut microfloral enzyme activities, hepatic activation of dietary mutagens and hepatic DNA adducts by 32P-postlabelling. Activation in vitro of the dietary mutagens 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by hepatic S9, formation of endogenous hepatic DNA adducts in vivo and the beta-glucuronidase activity of caecal contents were all increased in the sequence high fat > high fibre > high beef = control. Of the two DNA adducts found in all HFA rats, only one was present in GF controls, indicating that the human gut microflora (subject to human dietary modulation) either releases a DNA-adducting product able to act outside the gastrointestinal tract, or stimulates the generation of such a product by mammalian processes. Caecal nitrate reductase activity was highest in rats fed the high beef diet, whilst entrapment of cross-linking agents was highest in those fed the high fibre diet. These results show that risk-related components of human diets interact with human gut microflora to modulate the production of endogenous DNA-adducting and cross-linking substances.
Asunto(s)
Cocarcinogénesis , Grasas de la Dieta/toxicidad , Fibras de la Dieta/toxicidad , Proteínas en la Dieta/toxicidad , Intestinos/microbiología , Animales , Biotransformación , Ciego/enzimología , Reactivos de Enlaces Cruzados , Daño del ADN , Grasas de la Dieta/farmacocinética , Fibras de la Dieta/farmacocinética , Proteínas en la Dieta/farmacocinética , Composición de Medicamentos , Glucuronidasa/metabolismo , Humanos , Imidazoles/farmacocinética , Imidazoles/toxicidad , Masculino , Neoplasias Experimentales/etiología , Nitrato-Reductasa , Nitrato Reductasas/metabolismo , Polietileneimina , Quinolinas/farmacocinética , Quinolinas/toxicidad , Ratas , Ratas Endogámicas F344RESUMEN
The adsorption of 1,8-dinitropyrene (DNP) to alpha-cellulose has been studied as a model system for examining the adsorption of a hydrophobic mutagen to dietary fiber. Most of the DNP rapidly disappeared from an aqueous solution and partitioned between the glass wall of the test tube and the alpha-cellulose. Factors affecting DNP distribution included (i) the time of incubation, (ii) the final concentration of the solvent, dimethyl sulphoxide, in which the DNP has been dissolved, and (iii) the relative concentrations of DNP and alpha-cellulose. We suggest that this model system could be applied to other mutagens, and that alpha-cellulose would provide a useful standard fiber to permit inter-laboratory comparisons.
Asunto(s)
Celulosa/farmacología , Fibras de la Dieta/farmacocinética , Pirenos/farmacocinética , Salmonella typhimurium/genética , Adsorción , Dimetilsulfóxido/toxicidad , Pruebas de Mutagenicidad , Pirenos/toxicidad , Salmonella typhimurium/efectos de los fármacosRESUMEN
The hypolipidaemic effect of guar gum (30 g/day) was examined in a double blind placebo-controlled crossover study in 9 patients with primary hyperlipidaemia. The treatment periods were of six weeks duration. Cholesterol levels in low density lipoprotein (LDL) were decreased by 11.5% and in intermediate density lipoprotein (IDL) by 10.7%. Plasma cholesterol levels were reduced by 9.6% (P less than 0.05). Kinetic studies using autologous 125I-labelled LDL showed a decrease of 21.6% in plasma LDL apo B pool size (P less than 0.05) that resulted from a 39.1% increase in its fractional rate of catabolism. The kinetic effects of guar gum on LDL metabolism appear similar to that of bile acid binding resins in that LDL apo B fractional catabolism is greatly increased while there is a slight increase in production rate.
Asunto(s)
Fibras de la Dieta/metabolismo , Galactanos/uso terapéutico , Hipobetalipoproteinemias/tratamiento farmacológico , Hipolipoproteinemias/tratamiento farmacológico , Lipoproteínas LDL/metabolismo , Mananos/uso terapéutico , Anciano , Fibras de la Dieta/farmacocinética , Método Doble Ciego , Femenino , Galactanos/farmacocinética , Humanos , Hipobetalipoproteinemias/metabolismo , Lipoproteínas LDL/farmacocinética , Masculino , Mananos/farmacocinética , Persona de Mediana Edad , Placebos , Gomas de Plantas , Ensayos Clínicos Controlados Aleatorios como AsuntoRESUMEN
1. To evaluate the effect of age, sex and level of intake on the colonic response to wheat fibre, thirty healthy volunteers aged 17-62 years (nineteen men, eleven women) recruited from a local industry, were divided into four groups and given a controlled diet for two 3-week periods. The diet contained white bread during one period or one of four different amounts of bran-enriched wholemeal bread during the other (30, 60, 110, 170 g/d). 2. Wide variation was observed between subjects in stool weight on the basal diet and in response to wheat fibre. Stepwise regression analysis showed that the variation in stool weight was significantly related to sex (t 4.0, P less than 0.001) but not to age, height, weight or energy:fibre intakes on the basal diet. Stool weight in men (162 (SE 11) g/d) was approximately double that in women (83 (SE 11) g/d). Transit time and stool weight were closely related and the effect of sex on stool weight could be explained entirely by differences in transit. 3. The increase in stool weight with fibre was significantly related to dose (t 4.18, P less than 0.001) with approximately 1 g non-starch polysaccharides (the main component of dietary fibre) increasing stool weight by 5 g/d. Smaller increases in stool weight were seen in females, persons with initially low stool weights and small people. 4. Faecal carbohydrate excretion increased with the addition of bran mainly due to increased amounts of cellulose and pentose (arabinose + xylose), whilst digestibility of dietary non-starch polysaccharide fell from 77.6 (SE 2.3)% on the white bread diet to 65.6 (SE 2.4)% with the added bran (t 7.4, P less than 0.01, n26). 5. Faecal pH was more acid in men than in women and was related to methane production. Methane producers had higher faecal pH than non-producers (7.06 (SE 0.11) v. 6.65 (SE 0.1], lower stool weight (g/d; 93 (SE 12) v. 156 (SE 13] and slower transit times (h; 84.6 (SE 11.7) v. 48.6 (SE 6.6]. 6. These studies show that, when on similar diets, women have much lower stool weights and slower transit times than men. Furthermore, within the range of amounts of wheat fibre used in this and other published work, stool weight increases in linear proportion to the dose of fibre added to the diet. Methane excretion in breath is associated in this group of subjects with slow transit time and high faecal pH.
Asunto(s)
Envejecimiento/fisiología , Fibras de la Dieta , Ingestión de Alimentos , Intestino Grueso/fisiología , Caracteres Sexuales , Triticum , Adolescente , Adulto , Peso Corporal , Fibras de la Dieta/farmacocinética , Heces/análisis , Femenino , Humanos , Concentración de Iones de Hidrógeno , Lípidos/sangre , Masculino , Metano/análisis , Persona de Mediana Edad , Minerales/sangre , Factores de TiempoRESUMEN
1. The effect of extrusion cooking of a high-fibre cereal product on digestibility of starch, fibre components and phytate in the stomach and small intestine was studied by in vivo digestion in ileostomy subjects, as well as its effect on ileostomy losses of fat, nitrogen, sodium and potassium. 2. Seven ileostomy subjects were studied during two periods (each of 4 d) while on a constant low-fibre diet supplemented with 54 g/d of a bran-gluten-starch mixture (period A) or the corresponding extruded product (period B). 3. Extrusion cooking, using mild conditions, did not change the content of starch, dietary fibre components or phytate of the bran product, but the phytase (EC 3.1.3.26) activity was lost. During the period using the extruded bran product, there was a significant increase in recovery of phytate-phosphorus (period A, 44% of intake; period B, 73% of intake). The amount of fibre components, fat, fatty acids, N, Na, K, water and the ash weight of the ileostomy contents did not differ between the two periods. Only 0.6 and 0.7% respectively of ingested starch was recovered in ileostomy contents in periods A and B, while the fibre components were almost completely recovered. 4. Extrusion cooking, using even mild conditions, may lead to a considerable impairment in the digestion of phytate, probably due to a qualitative change in phytate and a loss of phytase activity. Starch, before and after extrusion cooking, is almost completely digested in the stomach and small intestine while fibre components are digested to a very small extent.
Asunto(s)
Culinaria , Fibras de la Dieta , Digestión , Grano Comestible , Intestino Delgado/metabolismo , Absorción , Adulto , Grasas de la Dieta/farmacocinética , Fibras de la Dieta/farmacocinética , Proteínas en la Dieta/farmacocinética , Femenino , Contenido Digestivo/análisis , Humanos , Ileostomía , Masculino , Persona de Mediana Edad , Ácido Fítico/farmacocinética , Ácido Fítico/orina , Almidón/farmacocinéticaRESUMEN
1. The effect of extrusion cooking, using mild conditions, of a high-fibre cereal product on apparent small bowel absorption of zinc, iron, calcium, magnesium and phosphorus was studied. 2. Seven ileostomy subjects were studied during two periods (each of 4 d), on a constant low-fibre diet supplemented with either 54 g/d of a bran-gluten-starch mixture or the corresponding extruded product. 3. The apparent absorption of Zn, Mg and P was significantly decreased (P less than 0.05) during the period with extruded product compared with the period with bran-gluten-starch. No difference was found for Fe and Ca. 4. The negative effect of extrusion cooking of a product containing phytic acid on availability of Zn, Mg and P was small but could be of nutritional relevance in foodstuffs that are consumed frequently and in infant formulas.