I . Four pigs initially of 30 kg live weight were surgically prepared with two re-entrant cannulas in the jejunum 1.0 m apart which allowed an isolated loop to be formed through which solutions were perfused. Wr-EDTA was used as a marker for measuring net secretion or absorption.2. A new Ringer solution was made, the ionic content of which resembled more closely that found in the jejunum of pigs given similar diets, than Krebs-Ringer solution.3. The absorption of glucose and water from Krebs-Ringer and new Ringer solutions was compared. 4.The effect of guar gum on the absorption of glucose and water from solutions of glucose and maltose was studied.5. There was a trend (not significant) for greater absorption of glucose and water from the new Ringer solution than from the Krebs-Ringer solution.6. Guar gum significantly reduced the net absorption of glucose from glucose or maltose solutions from 74.2 to 41.4% (P i 0401) and 71.1 to 35.0% (P < 0.001) respectively. 7.Guar gum significantly reduced the net absorption of water from the glucose solution from 42.7 to 8.3% (P < 0.01) and from the maltose solution from 49.2 to 5.1% (P < 0@01).8. The lack of differences between the absorption of glucose from solutions of glucose or maltose suggested that maltase (EC 3.2.1.20) activity was not inhibited to the extent that this limited the rate of glucose absorption.The beneficial effects of guar gum on glucose tolerance in normal (Jenkins et al. 1977) and diabetic (Jenkins et al. 1976) man are well established. The principal effect of adding guar gum to the diet is a decrease in postprandial hyperglycaemia. However, its mode of action remains unclear. Several hypotheses have been proposed to explain its action within the gut. These include a reduced rate of emptying of the stomach, altered motility in the stomach and small intestine, poorer mixing of digesta and enzymes in the gut lumen, slower hydrolysis of dietary components by brush-border enzymes in the small intestine and a reduction in the rate of absorption across the epithelial cell membrane (Low et al.
1. Five pigs initially of 40-50 kg live weight were fitted with simple gastric cannulas which permitted complete evacuation and sampling of gastric digesta once daily.2. Theeffects ofaddition of fourtypesofdietary fibre(wheat bran (WB; 40 g/kg), sodiumcarboxymethylcellulose (CMC; 40 g/kg), high-methoxy citrus pectin (Pe; 40 g/kg) and granulated guar gum (G; 40 g/kg)) on gastric emptying of a semi-purified diet during 4 h following a meal were measured. 3.Each of the test diets and the control diet (C) were given to each pig for 1 week using a 5 x 5 Latin-square arrangement. Digesta were collected before and 0.5, 1, 2 or 4 h after feeding on the last 5 d of each week.4. The mean gastric pH was not significantly affected by diet except 2 h after feeding (CMC higher than C) and 4 h (Pe, G and CMC higher than C).5. Compared with diet C, the rate of gastric emptying of digesta was significantly slower for diet G , I, 2 and 4 h after feeding, and 2 and 4 h after feeding for diet CMC.6. The rates of gastric emptying of digesta components were not significantly reduced by dietary fibre except for dry matter (DM) (diet CMC 2 h and diet B 4 h after feeding), total nitrogen (TN)(diet G 2 h after feeding) and total glucose (diet Pe 2 h after feeding).7. There were no significant effects of diet on trichloroacetic-acid-soluble N :TN. 8. When gastric emptying was expressed in terms of half-time (T5J values, significant increases (compared with diet C) were found for digesta (diets G and CMC), DM (diet WB) and TN (diet G ) .9. The apparent viscosity of the gastric digesta was significantly higher when diets Pe, G, and CMC were given than diets C or WB. Diets Pe and CMC were very viscous in the meal before ingestion, but diet G was not; its high viscosity developed after it had reached the stomach.10. It is concluded that although those types of dietary fibre which increased meal or gastric viscosity reduced the rate of gastric emptying of digesta, this effect was confined to the liquid phase, because DM, total glucose and TN emptying were largely unaffected. The hypothesis that a reduced rate of gastric emptying may be an important determinant of the decreased rates of glucose absorption observed when such sources of dietary fibre are eaten is not supported by the results presented.In recent years there has been great interest in the use of high-carbohydrate-high-fibre diets for the treatment of diabetics (Jenkins et al. 1980;Simpson, 1981). Of particular interest are those soluble forms of dietary fibre which increase meal viscosity (Jenkins Rr Wolever, 1981) and reduce the peak concentration of peripheral blood glucose levels after a test meal (Jenkins et al. 1978); it was suggested that this effect might be due, at least in part, to a reduction in the rate of gastric emptying. However, not all forms of dietary fibre are of equal value in reducing postprandial hyperglycaemia and hyperinsulinaemia when added to a test meal in man (Jenkins et al. 1978).Jenkins et al. (1978) found that powdered guar gum was the most effective ...
I . Simple gastric cannulas were surgically fitted to four pigs, initially of 30 kg live weight, to examine the effects of guar gum on gastric emptying.2. Four semi-purified high-fat diets based on starch, casein, soya-bean oil and tallow were given to each pig. They contained 0 (control), 20,40 or 60 g powdered guar gum/kg diet. The meals as fed contained 257 g dry matter (DM)/kg. 3.The contents of the stomach were evacuated, with rinsing, before feeding or 0.5, I , 2 or 4 h after feeding. 4. The mean pH of the digesta was unaffected by guar gum until 4 h after feeding when the value increased as the amount of guar gum in the diet rose.5. The only significant effects of guar gum on the emptying of digesta and its components (compared with the control diet) were to reduce the rate of emptying of (a) digesta 1 h after feeding (60 g/kg diet) and 4 h after feeding (40 and 60 g/kg diets), (b) dry matter and glucose 1 h after feeding (60 g/kg diet), (c) nitrogen 1 h after feeding (60 g/kg diet) and 4 h after feeding (40 and 60 g/kg diets).6. When expressed on a half-time (Tho) basis, the emptying of digesta and N (but not of DM and glucose) were significantly slower for diets containing 40 and 60 g guar gum/kg than for the control diet.7. The apparent viscosity of the gastric digesta ranged between 0.5 and 23.7% of the values for the diets as consumed.8. It was concluded that the effects of guar gum on gastric emptying of high-solid meals were small, and that this was unlikely to be an important aspect of the mechanism by which guar gum reduces postprandial blood glucose concentrations.
1. Existing information on whether the action of guar gum in decreasing postprandial blood glucose concentrations is due, at least in part, to a reduced rate of gastric emptying is conflicting, possibly because three types of test meals have been used. In order to test whether the type of test meal used influences the action of guar gum, these three types of meal were compared, either without or with guar gum, in growing pigs. The meals were: a high-energy meal (HEM), a low-energy milky drink (LEMD) and a glucose drink (GD).2. Six pigs were prepared with a simple gastric cannula which allowed complete removal of the stomach contents just before or 0.5, 1, 2 or 4 h after feeding.3. The three types of test meal without guar gum gave rise to very different postprandial profiles of gastric pH and of digesta and dry matter (DM) emptying from the stomach. 4. Addition of guar gum' to the G D significantly raised gastric pH at 0.5 and 1 h after feeding but, when it was added to HEM, gastric pH was only significantly raised 4 h after feeding. No significant effect on gastric pH was seen when guar gum was added to LEMD.5. Although addition of guar gum to G D had no significant effect on the emptying of digesta from the stomach, when added to HEM the rate of emptying of digesta was significantly reduced I, 2 and 4 h after feeding. Addition of guar gum to LEMD only significantly increased the amount of digesta remaining in the stomach 2 h after feeding.6. There was no significant effect on the emptying of DM from the stomach when guar gum was added to either HEM or LEMD. However, addition of guar gum to G D significantly reduced the mean rate of emptying of DM 0.5 h after feeding.7. Addition of guar gum to either LEMD or G D had no significant effect on the DM concentration of the evacuated gastric digesta. However, addition of guar gum to HEM significantly lowered the DM concentration of the evacuated gastric digesta I , 2 and 4 h after feeding.8. It was concluded that differences in test meal composition and also in the methods used to measure gastric emptying could account for the discrepancies previously reported. The results suggest that although guar gum may reduce the rate of gastric emptying under some conditions, this is unlikely to be the only mechanism by which it acts.Although the beneficial effects of guar gum on glucose tolerance (in particular, by reducing postprandial blood glucose levels) in normal and diabetic man are well established, its detailed mode of action remains unclear. Jenkins et al. (1978) suggested that these effects might be the result of a reduced rate of gastric emptying but studies designed to investigate this hypothesis have given conflicting results. We have recently found that guar gum had little effect on the gastric emptying rate of dry matter (DM) (and thus of glucose) from high-energy meals in pigs prepared with a simple gastric cannula (Rainbird & Low, 1986). This contrasts with the reductions caused by guar gum in the gastric emptying rate of (1) a glucose solution given by oroga...
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